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INTERCHANGEABILITY OF INFRARED AND CONDUCTIVE DEVICES FOR THE MEASUREMENT OF HUMAN SKIN
TEMPERATURE
Aaron James Edward Bach Bachelor of Exercise and Movement Sciences
Submitted in fulfilment of the requirements for the degree of
HL84: Master of Applied Science (Research)
Exercise and Nutrition Sciences
Faculty of Health
Queensland University of Technology
2014
Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature i
Keywords
Conduction, Cutaneous Temperature, Exercise, Exercise Physiology, Infrared,
Radiation, Recovery, Skin Temperature, Thermography, Thermometry,
Thermophysiology, Thermoregulation, Tissue Temperature.
ii Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature
Abstract
The skin is the site of reciprocal heat transfer between the human body and the
external environment. Consequently, the assessment of skin temperature is extremely
important in sports medicine, exercise science, occupational, clinical and public
heath settings. Currently there is no gold standard for the measurement of skin
temperature. The primary methods of measuring 𝑇sk are derived from conductive
(contact) and infrared devices. These techniques apply different scientific principles
of thermal heat transfer. Conductive methods are based upon thermal conduction as a
result of physical contact between the object of interest and the measurement device.
While, infrared devices determine temperature by detecting infrared thermal
radiation being emitted from the skin.
Current practice suggests that for any skin temperature devices to be
considered interchangeable, temperature differences should not exceed the proposed
clinical significant difference of 0.5 °C. This relativity small temperature difference
represents the maximum allowable disagreement between 𝑇sk devices, and any
deviation outside of these limits could produce erroneous data that significantly
influences the conclusions drawn by researchers and clinicians. Unfortunately,
despite widespread use throughout clinical and exercise science settings the scientific
evidence supporting the interchangeability of infrared thermometry with more
traditional conductive instruments is limited and equivocal. Therefore, the purpose of
this thesis was to investigate the interchangeability of conductive and infrared means
of skin temperature measurement under a variety of conditions.
This was conducted through an initial systematic review of the current
literature pertaining to conductive and infrared device interchangeability (Chapter 3).
The key findings of this review was 1) there is no trend for conductive or infrared
devices to consistently overestimate 𝑇sk compared to one another; 2) conductive and
infrared devices are not interchangeable under resting thermoneutral conditions; and
3) that more high-quality studies are needed that compare devices in the presence of
environmental and physical stressors before further conclusions can be drawn
regarding their interchangeability.
In addition to the systematic review, two original investigations were
conducted. The first was to ensure accurate data collection for the primary study via
Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature iii
the calibration of skin temperature measurement devices (Chapter 4) and identify a
comparison device to be used in a subsequent human investigation. Conductive and
infrared devices were calibrated against a certified thermometer in a stirred waterbath
through the expected physiological skin temperature range (11 temperatures between
20 and 42 °C) prior to experimental data collection. A linear regression was
subsequently developed for each device before human testing, allowing for a
correction to be applied following human data collection.
The second investigation (Chapter 5) aimed to answer the primary research
question, are conductive and infrared techniques of skin temperature measurement
interchangeable under a variety of conditions under a variety of conditions? Thirty
healthy males had mean skin temperature measured simultaneously with the four
skin temperature devices used in Chapter 4. Measurements were taken every 3-min
from four regions of interest (neck, scapular, hand and shin) during 30-min of
thermoneutral rest (24.0 ± 1.3 56 ± 9% relative humidity), 30-min of cycle ergometry
in the heat (38.0 ± 0.5 °C, 41 ± 2% relative humidity) and 45-min of thermoneutral
recovery. Systematic errors exceeding statistical (P < 0.05) and clinical (>0.5 °C)
significance were observed between conductive and infrared devices throughout all
conditions. A significant main effect for device, time and their interaction was
observed in all three periods for 𝑇�sk (P < 0.05). Mean differences ± SD between the
thermistor and iButton® (rest, exercise and recovery) were as follows: -0.01±0.2°C, -
0.25±0.42°C, -0.37±0.5°C; thermistor and infrared thermometer: -0.34±0.22°C,
0.46±0.63°C, -1.04±0.89°C; thermistor and infrared camera (rest, recovery): -
0.83±0.39°C, -1.88±0.95°C. Pairwise comparisons of 𝑇�sk revealed significant
differences (P < 0.05) between TM and both infrared devices during resting
conditions, and significant differences (P < 0.05) for comparisons between the TM
and all other devices tested during exercise and recovery. Furthermore, devices that
were within acceptable agreement during rest, failed to be classified as
interchangeable under environmental or external interventions (i.e., exercise in the
heat).
In summary the findings of this thesis suggest that clinical and significant
differences exist between conductive and infrared devices which are commonly
employed in the assessment of human 𝑇sk in exercise science, research and clinical
settings. This has important implications given the wide variety of commercially
iv Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature
available 𝑇sk measurement devices available to the public. Accurate comparisons
between publications using different 𝑇sk measurement methods may not be possible
under resting, exercise and high ambient conditions which depict different
thermoregulatory responses. These significant differences between conductive and
infrared means could potentially influence the interpretation of results, diagnosis and
therefore treatment outcomes for clinical and exercise science applications.
v Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature
Table of Contents Keywords ................................................................................................................................................. i
Abstract .................................................................................................................................................. ii
List of Figures ..................................................................................................................................... viii
List of Tables ......................................................................................................................................... ix
List of Abbreviations .............................................................................................................................. x
Glossary of Terms ................................................................................................................................. xii
Statement of Original Authorship ........................................................................................................ xiv
Acknowledgements .............................................................................................................................. .xv
CHAPTER 1: INTRODUCTION ....................................................................................................... 3 1.1 Background and rationale for research ........................................................................................ 3
1.2 Aim of research ............................................................................................................................ 4
1.3 Objectives of research .................................................................................................................. 4 1.4 Thesis Hypotheses ....................................................................................................................... 4
1.5 Thesis Outline .............................................................................................................................. 5
CHAPTER 2: LITERATURE REVIEW ........................................................................................... 7 2.1 Introduction.................................................................................................................................. 7
2.2 Thermodynamics ......................................................................................................................... 7
2.3 Mechanisms of Heat Exchange in the Human Body ................................................................... 8 2.4 Thermoregulation and Skin Temperature .................................................................................. 10
2.4.1 Rest 10 2.4.2 Exercise .......................................................................................................................... 11 2.4.3 Extreme Environments ................................................................................................... 13
2.5 Mean Skin Temperature ............................................................................................................. 15
2.6 Applications of Skin Temperature MeasurEment ...................................................................... 17 2.7 Characteristics That Influence Human Skin Temperature ......................................................... 20
2.7.1 Inherent ........................................................................................................................... 20 2.7.2 Behavioural..................................................................................................................... 26
2.8 Skin Temperature Measurement Techniques ............................................................................. 29 2.8.1 Conductive Devices ........................................................................................................ 30 2.8.2 Considerations When Using Conductive Devices .......................................................... 31 2.8.3 Infrared Devices ............................................................................................................. 33 2.8.4 Considerations When Using Infrared Devices ................................................................ 35
2.9 Defining Interchangeablilty ....................................................................................................... 37
2.10 Conclusion ................................................................................................................................. 37
CHAPTER 3: ARE CONDUCTIVE AND INFRARED DEVICES FOR MEASURING SKIN TEMPERATURE INTERCHANGEABLE? A SYSTEMATIC REVIEW ................................... 39 3.1 Introduction................................................................................................................................ 39
3.2 Method ....................................................................................................................................... 42 3.2.1 Search Strategy ............................................................................................................... 42 3.2.2 Inclusion Criteria ............................................................................................................ 43 3.2.3 Data Extraction and Management .................................................................................. 43
3.3 Results ....................................................................................................................................... 50 3.3.1 Included studies .............................................................................................................. 50
Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature vi
3.3.2 Detail of Comparisons .................................................................................................... 50 3.3.3 Risk of bias ..................................................................................................................... 51 3.3.4 Study heterogeneity ........................................................................................................ 52 3.3.5 Cold Environment and Cryotherapy ............................................................................... 52 3.3.6 Thermoneutral Environment ........................................................................................... 53 3.3.7 Hot Environment ............................................................................................................ 53
3.4 Discussion .................................................................................................................................. 55 3.4.1 Evaluation of Methodological Quality............................................................................ 55 3.4.2 Summary of Findings ..................................................................................................... 55 3.4.3 Limitations and Future Research .................................................................................... 57
3.5 Conclusions ................................................................................................................................ 57
CHAPTER 4: CORRECTION FORMULA OF INFRARED AND CONDUCTIVE THERMOMETRY .............................................................................................................................. 61 4.1 Introduction ................................................................................................................................ 61 4.2 Methods ..................................................................................................................................... 62
4.2.1 Experimental overview ................................................................................................... 62 4.2.2 Measurement Devices and Procedures ........................................................................... 64 4.2.3 Statistical Analysis.......................................................................................................... 65
4.3 Results ........................................................................................................................................ 66
4.4 Discussion .................................................................................................................................. 70 4.4.1 Limitations and Future Research .................................................................................... 72
4.5 Conclusion ................................................................................................................................. 72
CHAPTER 5: MEAN SKIN TEMPERATURE ASSESSMENT DURING REST, EXERCISE IN THE HEAT AND RECOVERY: DIFFERENCES BETWEEN CONDUCTIVE AND INFRARED DEVICES ....................................................................................................................... 75 5.1 Introduction ................................................................................................................................ 75
5.2 Methods ..................................................................................................................................... 76 5.2.1 Participants ..................................................................................................................... 76 5.2.2 Pre-experimental Protocol .............................................................................................. 77 5.2.3 Experimental Protocol .................................................................................................... 78 5.2.4 Measurements and Equipment: ....................................................................................... 81 5.2.5 Statistical Analysis.......................................................................................................... 86
5.3 Results ........................................................................................................................................ 87
5.4 Discussion .................................................................................................................................. 89
5.5 Conclusion ................................................................................................................................. 94
CHAPTER 6: CONCLUSIONS ........................................................................................................ 95
APPENDICES ..................................................................................................................................... 99 Appendix A Ethics Approval ..................................................................................................... 99 Appendix B Health Screen Questionnaire ............................................................................... 100 Appendix C Informed Consent ................................................................................................ 102 Appendix D Complete graphed data for mean skin temperature and all individual sites ........ 107 Appendix E Complete ANOVA outputs for all sites and conditions ....................................... 117 Appendix F Complete post-hoc paired sample T-test comparisons between all devices ......... 122
REFERENCES .................................................................................................................................. 127
viii Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature
List of Figures
Figure 2.1 The electromagnetic spectrum, depicting various properties including visible light and long-wave infrared radiation ......................................................................................... 34
Figure 3.1. PRISMA flow chart describing the selection and exclusion of articles.............................. 43
Figure 3.2. Included Studies: risk of bias summary. ............................................................................. 50
Figure 3.3. Forest plot, skin temperature comparison for 8 of the 9 included studies: Conductive vs. Infrared, outcome: mean skin temperature difference. # Based upon values derived from publication; * data received from correspondence with first author; C4 = Cervical vertebrae 4; L4 = Lumbar vertebrae 4; T1 = Time 1; ITD = 3000A (Genius, Sherwood IMS, California, USA); ITE = DT-1001 (Exergen, Massachusetts, USA). .......................................................................................................... 52
Figure 4.1. Bland–Altman plot of the certified thermometer and a) thermistor 5; b) iButton® 7; c) infrared thermometer; d) infrared camera across eleven water bath temperatures. Solid black line indicates the mean difference (MD); dashed lines represent the 95% limits of agreement (LoA). ................................................................................................... 66
Figure 5.1. Four skin temperature measurement regions of interest in accordance with International Organisation for Standardisation - 9886. 1) back of neck; 2) inferior border of right scapula; 3) dorsal right hand; 4) proximal third of right tibia. ..................... 77
Figure 5.2. Timeline of data collection protocol. 𝑇�𝑠𝑘 = Mean Skin Temperature; TM = Thermistor; IB = iButton®; IT = Infrared Thermometer; IC = Infrared Camera. ................. 78
Figure 5.3. Example of regions of interest captured via infrared thermography. a) Hand b) Neck and Scapula c) Shin. ................................................................................................... 83
Figure 5.4. a) Diagram of template dimensions used on each of the four skin sites; b) example of the randomised layout of marked and placed devices on a male subject’s shin; IB: iButton®, IT: Infrared Thermometer, TM: Thermistor, IC: Infrared Camera. ...................... 84
Figure 5.5. Mean skin temperature (n=30) of all tested devices during rest (4 devices), exercise (3 devices) and recovery (4 devices). a = IB clinically (>0.5 °C) and significantly (P < 0.001) different from TM; b = IT clinically (>0.5 °C) and significantly (P < 0.001) different from TM; c = IC clinically (>0.5 °C) and significantly (P < 0.001) different from TM. TM: Thermistor; IB: iButton®; IT: Infrared Thermometer; IC: Infrared Camera. ................................................................................................................................ 86
Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature ix
List of Tables
Table 2.1. Commonly used 𝑇�sk formula, including site and weighting. ................................................ 16
Table 2.2. Examples of 𝑇sk changes used to aid in the diagnosis of illness and injury. ....................... 25
Table 3.1. Description of devices .......................................................................................................... 41 Table 3.2. Details of articles included in the systematic review ........................................................... 45
Table 4.1. Device specifications ............................................................................................................ 61
Table 4.2. Mean difference and measures of variation for all tested contact sensors in comparison to the certified thermometer. ............................................................................ 67
Table 4.3. Calibration formula for all devices. ..................................................................................... 68
Table 5.1. Participant characteristics, values are mean ± standard deviation (range). ....................... 75 Table 5.2. Device specifications ............................................................................................................ 80
x Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature
List of Abbreviations
ε Emissivity
∑SKF Sum of Skinfolds
°C Degrees Celsius
µm Micrometres
ANOVA Analysis of Variance
ASTM American Society for Testing and Materials
BM Body Mass
BMI Body Mass Index
CI 95% Confidence Intervals
H0 Null Hypothesis
HSK Net Heat Loss from the Skin
HZ Hertz
IB iButton®
IC Infrared Camera
IT Infrared Thermometer
kg Kilograms
KSK Conduction of Skin
LoA Limits of Agreement
m Metres
MD Mean Difference
mm Millimetres
NIST National Institute of Standards and Technology
nm Nanometres
O2 Oxygen
Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature xi
RH Relative Humidity
SD Standard Deviation
SE Standard Error
Tc Core Temperature
Thand Hand Skin Temperature
TM Thermistor
Tneck Neck Skin Temperature
Troom Room Temperature
Tscapular Scapular Skin Temperature
Tshin Shin Skin Temperature
𝑇sk Skin Temperature
𝑇�sk Mean Skin Temperature
xii Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature
Glossary of Terms
Calibration: A methodical measurement procedure to determine all the parameters
significantly affecting an instrument’s performance.
Emissivity: A dimensionless quality that represents the ratio of infrared energy
radiated by an object at a given temperature and spectral band to the energy emitted
by a perfect radiator (blackbody) at the same temperature and spectral band. The
emissivity of a perfect blackbody is unity (1.00) (Thomas, 2006).
Error: the difference between an observed of calculated value and a true value.
Composed of random (affects reliability) and systematic (affects validity) error.
iButton®: A wireless, self-enclosed and programmable, contact device that stores
temperature values in an internal memory for retrospective extraction (Harper
Smith, Crabtree, Bilzon, & Walsh, 2010).
Infrared (Handheld) Thermometer: Typically a stand-alone, non-contact, point-
and-shoot device that displays a single digital temperature reading by measuring
infrared energy at a localised ‘spot’ area of the skin (Thomas, 2006).
Infrared: The portion of the electromagnetic spectrum extending from the far red,
visible at approximately 0.75 to 1000 µm. However, because of instrument design
considerations all infrared measurements in this thesis were made between 7.5-14µm
(Thomas, 2006).
Infrared Thermal Imaging (Camera): detects infrared energy as a function of
temperature and converts the electronic video signal into an image displayed on a
connected computer, with each pixel representing a single temperature data point.
Interchangeability: the sufficient agreement between two different methods of data
collection, allowing for the substitution of methods without producing significant
measurement differences (Bland & Altman, 1986).
Reliability: the extent to which an experiment, test, or measuring procedure yields
the same results on repeated trails.
Repeatability: the closeness of agreement between the results of successive
measurements carried out under the same conditions of measurement.
Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature xiii
Reproducibility: the closeness of agreement between the results of successive
measurements carried out under changed conditions of measurement.
Temperature: A degree of hotness or coldness of an object measurable by a specific
scale, where heat is defined as thermal energy in transit and flows from objects of
higher temperature to objects of lower temperature (Thomas, 2006).
Thermistor: A surface temperature probe - that requires contact with the object of
interest - uses an internal temperature sensitive resistor that measures temperature by
using a non-linear relationship between resistance and temperature.
Thermography: the product of data collection via an infrared means used to
measure temperature variations on the surface of the body (Blatteis et al., 2001).
Thermometry: the measurement of temperature typically associated with
conductive (contact) devices.
Thermoneutral Temperature: The range of ambient temperature at which
temperature regulation is achieved only by control of sensible heat loss and therefore
is different when insulation, posture or metabolic rate varies (Blatteis et al., 2001).
An example of a thermoneutral temperature for a resting lightly clothed human
would be between 22 and 26 °C (de Dear & Brager, 2002).
Thermoregulation: Maintenance of a constant internal body temperature
independent from the environmental temperature.
Validity: the extent to which a situation as observed reflects the true situation, of the
degree to which data collected by a measure are correct or true.
xiv Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature
Statement of Original Authorship
The work contained in this thesis has not been previously submitted to meet
requirements for an award at this or any other higher education institution. To the
best of my knowledge and belief, the thesis contains no material previously
published or written by another person except where due reference is made.
Signature:
Date: 20/06/2014
QUT Verified Signature
Interchangeability of Infrared and Conductive Devices for the Measurement of Mean Skin Temperature xv
Acknowledgements
There are a number of people without whom this thesis would not have been
written, and to whom I am greatly indebted.
First and foremost, my most sincere thanks must go to my supervisors, Dr.
Joseph Costello and Associate Professor Ian Stewart, both of whom have supported
me above and beyond my expectations.
To my principle supervisor Dr. Joseph Costello, thank you for your patience,
direction and feedback for the duration of my Masters project. Your door was always
open to me whenever I needed your expertise, and I was encouraged after each
discussion with you.
To my associate supervisor Associate Professor Ian Stewart, thank you for the
guidance you have given me both before and throughout my post-graduate research.
Your advice has helped shape the direction in which my academic career is taking. In
addition to the emotional support, I am extremely grateful for your financial
assistance in the form of both a supervisor funded scholarship and employment as a
research assistant throughout my degree.
To my Mum and Dad, thanks for all the patience and encouragement in any
and all of my endeavours. My love and recognition goes to my partner Katrina, for
her unwavering support and perspective throughout my degree, without wanting for
anything in return. I would also like to acknowledge Katrina’s parents, Lex and Jen,
who welcomed me into their home to live during my entire tertiary education and
provided me with the love and support that has contributed to my success.
I would like to thank all of my participants who agreed to be a part of this
project and give a big thank you to both Alice Disher and David Borg. Without their
tireless efforts in assisting with data collection my research would not be possible.
Finally I would like to thank my fellow research students (Alice Disher,
Matthew Bourne) and QUT employees (Brittany Dias, David Borg) for their support
and encouragement throughout my studies.
Chapter 1: Introduction 1
Chapter 1: Introduction
1.1 BACKGROUND AND RATIONALE FOR RESEARCH
Skin temperature (𝑇sk) is an important physiological measure that can reflect
the presence of illness and injury as well provide insight into the localised
interactions between the body and the environment (Lim, Byrne, & Lee, 2008). 𝑇sk is
assessed in exercise science, occupational, surgical, clinical and public heath
settings. The measurements have a wide range of applications that consist of, but are
not limited to, the assessment of thermoregulatory responses (Wang, Zhang, Arens,
& Huizenga, 2007), identification of heat stress and physiological strain (Cuddy,
Buller, Hailes, & Ruby, 2013), evaluation of cryotherapy (Bleakley, Costello, &
Glasgow, 2012; Costello, Culligan, Selfe, & Donnelly, 2012), and the diagnosis of
disease (Wasner, Schattschneider, & Baron, 2002).
Methods of measuring 𝑇sk fall into two categories: conductive and infrared.
Conductive devices require direct contact with the skin and measure temperatures
through heat transfer via conduction (Tyler, 2011). Infrared devices detect emitted
radiation from the skin surface that is proportional to its temperature (Lahiri,
Bagavathiappan, Jayakumar, & Philip, 2012). Despite the differences in scientific
principles underpinning each method, many researchers and clinicians assume
interchangeability between devices under all circumstances.
Current practice suggests that for any other device to be considered
interchangeable temperature differences should not exceed the proposed clinical
significant difference of 0.5 °C (Joly & Weil, 1969; Kelechi, Good, & Mueller, 2011;
Kelechi, Michel, & Wiseman, 2006; Selfe, Whitaker, & Hardaker, 2008). This
relativity small temperature difference represents the maximum allowable
disagreement between 𝑇sk devices, and any deviation outside of these limits could
produce erroneous data that significantly influences the conclusions drawn by
researchers and clinicians. The implications of the current research could aid in the
understanding of which circumstances are most appropriate for conductive and
infrared 𝑇sk measures. Without this research and ensuing understanding of
measurement influences accurate comparisons between published studies using
varying methods may not be possible. Furthermore, the erroneous collection of data
2 Chapter 1: Introduction
could alter the interpretation of results, diagnosis and therefore treatment outcomes
for clinical and exercise science applications.
Existing studies into the interchangeability of devices vary in methodological
quality, are confined to a limited number of devices and were compared
predominantly resting thermoneutral conditions (Buono, Jechort, Marques, Smith, &
Welch, 2007; Burnham, McKinely, & Vincent, 2006; Kelechi et al., 2011; Kelechi et
al., 2006; Korukçu & Kilic, 2009; Matsukawa, Ozaki, Nishiyama, Imamura, &
Kumazawa, 2000; Roy, Boucher, & Comtois, 2006b; Ruopsa, Kujala, Kaarela,
Ohtonen, & Ryhänen, 2009; van den Heuvel, Ferguson, Dawson, & Gilbert, 2003).
The findings from these investigations suggest conductive and infrared devices may
not be interchangeable under resting thermoneutral conditions. However, due to
limited and ambiguous findings it is unclear if conductive and infrared devices are
interchangeable in the presence of internal (e.g. exercise) or environmental stimuli
(e.g. cold/heat exposure).
1.2 AIM OF RESEARCH
The primary aim of this thesis was to investigate the interchangeability of
conductive and infrared means of 𝑇sk measurement at rest in a thermoneutral
environment, during exercise in the heat and recovery.
1.3 OBJECTIVES OF RESEARCH
• To systematically review the literature addressing the interchangeability of
conductive and infrared 𝑇sk devices (Chapter 3).
• To calibrate two conductive and two infrared devices, commonly used in the
assessment of 𝑇sk, against a reference standard in a water bath (Chapter 4).
• To establish the most accurate of these four devices to use as a comparative
reference for the human investigation (Chapter 4).
• To compare and contrast measurements of conductive and infrared devices
during rest, exercise in the heat and recovery in humans (Chapter 5).
1.4 THESIS HYPOTHESES
For the studies completed, the null hypotheses were as follows:
Chapter 1: Introduction 3
Chapter 4: Calibration of infrared and conductive thermometry in a
water bath.
H0: Clinical significant differences (0.5 °C) between each device and the
certified thermometer will not be violated.
H0: Compared to the certified thermometer, the thermistor will be classified as
the most accurate of the four tested devices.
Chapter 5: Evaluation of contact and non-contact thermometry for
the measurement of mean skin temperature during rest,
exercise and recovery.
H0: Clinical significant differences between each device and the identified
reference device will not be violated under any of the tested conditions.
1.5 THESIS OUTLINE
This thesis is comprised of six chapters. Following a brief introduction to the
research topic and an outline of the primary aim and objectives of the thesis in the
current chapter (Chapter 1), a traditional literature review and a systematic review of
the current literature are presented (Chapters 2 and 3, respectively). Chapters 4 and 5
comprise of two original investigations presented in manuscript format. Finally,
Chapter 6 will conclude the findings of this research and recommend future
directions.
Chapter 2: presents a review of the relevant literature pertaining to human
thermoregulation, mechanisms for heat transfer and 𝑇sk application and techniques.
This review identifies the existing research in the broader area of 𝑇sk and is a prelude
for a more specific systematic review on device interchangeability in the subsequent
chapter (Chapter 3).
Chapter 3: systematically reviews the relevant literature on the
interchangeability of conductive and infrared 𝑇sk devices. This review identifies
existing research in the area, appraises the methodological and statistical analyses
used in the individual studies and establishes the significance to exercise science
applications. In addition Chapter 3, section 3.4.3 Limitations and Future Research
proposes a number of areas that warrant further investigation. These
4 Chapter 1: Introduction
recommendations formed the basis for the investigations undertaken as part of this
thesis (Chapters 4 and 5).
Chapter 4: establishes the means in which calibration of 𝑇sk devices can be
achieved in a stirred water bath. Chapter 4 was a preliminary investigation that
helped form the methodology of a comparison study on humans (Chapter 5). By
establishing a means by which to calibrate of 𝑇sk devices in a stirred water bath, data
collected from this investigation allowed for the calculation of calibration
coefficients for devices and identified the most accurate device to use as a
comparative tool in Chapter 5.
Chapter 5: is the product of the preceding chapters, with the investigation of
measurement differences between conductive and infrared devices for the assessment
of mean 𝑇sk in resting, exercise in the heat, and recovery conditions (n=30). Again,
this chapter is heavily influenced by the findings of Chapter 4 and addresses the
shortfalls of the identified literature in Chapter 3.
Chapter 6: summarises the results observed and the research completed
throughout this thesis. The practical implications of these findings are explored and
recommendations for future research are presented.
Chapter 2: Literature Review 7
Chapter 2: Literature Review
2.1 INTRODUCTION
This chapter will give a comprehensive overview into the mechanisms of
human heat exchange, thermoregulation and the importance of skin temperature
(𝑇sk). Further to this, the potential influences of human 𝑇sk and means in which 𝑇sk is
assessed will be examined. The subsequent chapter (Chapter 3) will specifically
compare all current publications regarding the measurement differences between
devices used to assess human 𝑇sk.
2.2 THERMODYNAMICS
Within thermodynamics, a system is classified as an object of interest, for
example a beaker of water, or the human skin. Factors influencing the system are
referred to as surroundings. The surroundings allow for the scientific observation of
the behaviour of the system, which in turn helps us to understand the system’s
properties. The thermodynamic laws that govern the behaviour of a system are
defined below (Atkins, 2010):
The Zeroth Law (Equilibrium): if two systems are in thermal equilibrium
with a third, then the first two systems are in thermal equilibrium with each
other.
The First Law (Conservation of Energy): the change in the internal energy
of a system is equal to the sum of the heat added to the system and the work
done on it.
The Second Law (Entropy): heat cannot be transferred from a colder to a
hotter body within a system without net changes occurring in other bodies
within that system.
The Third Law (Nernst Heat Theorem): it is impossible to reduce the
temperature of a system to absolute zero in a finite number of steps.
In order to quantify the thermodynamic motions of molecules that make up a
system (i.e., heat radiation, particle velocity, kinetic energy), three standard
temperature scales – degrees Celsius, degrees Kelvin and degrees Fahrenheit – have
8 Chapter 2: Literature Review
been established. Degrees Celsius (°C) is the most commonly used unit of
temperature measurement.
Thermal energy (unit = Joules) is the measurement term for the potential and
kinetic energy imparted on a system, by the surroundings, that alters its temperature
(Atkins, 2010). This heat can be transferred via four means of transfer; conduction,
convection, radiation and evaporation. The following section introduces each of
these mechanisms for thermal energy transfer in relation to humans.
2.3 MECHANISMS OF HEAT EXCHANGE IN THE HUMAN BODY
Human beings are classed as homeotherms, i.e., capable of sustaining a stable
body temperature, despite fluctuating ambient temperatures (Sawka, Latzka, Matott,
& Montain, 1998). Homeotherms are made up of two compartments, the inner core
and outer shell, or skin (Bouzida, Bendada, & Maldague, 2009). The inner core is
tightly regulated between 36 and 38 °C, depending on the ambient conditions, to
ensure healthy neurological (M. Kenney, Claassen, Bishop, & Fels, 1998),
musculoskeletal (Sawka & Wenger, 1988) and metabolic function (B. Nielsen,
Savard, Richter, Hargreaves, & Saltin, 1990).
The shell (i.e., skin) is the site of reciprocal heat transfer between the human
body and the external environment. This energy exchange occurs by means of
sensible heat transfer mechanisms (conduction, convection, radiation) and latent heat
transfer (evaporation), which allows the human body to absorb and release thermal
energy into the surrounding environment. When core temperature (Tc) rises, excess
heat energy is transferred from the core to the skin, and subsequently from the skin
into the environment.
Conduction
At a molecular level, conduction refers to the transfer of heat energy that
occurs in all substances (i.e., solid, liquid and gas) between hot, rapidly moving or
vibrating molecules (Lyklema, 2001). These faster (hotter) moving molecules
transfer some heat energy to colder neighbouring particles when they collide.
In the case of human heat transfer, conduction refers to the direct contact
between the body, typically the skin, and another surface. Heat is transferred from
the warmer body, proportionate to the size of the temperature gradient, surface area
Chapter 2: Literature Review 9
of contact, pressure between the two bodies and specific conductivity of the surfaces
(Hardy, Du Bois, & Soderstrom, 1938).
Conduction is the primary means of transferring metabolic heat energy from
the body’s core through to the skin (Keller & Seiler, 1971). As Tc rises as a product
of cellular metabolism, excess heat is transferred via conduction from deeper and
surrounding tissues to the skin surface where it can be transferred into the
environment (Prek & Butala, 2010).
Convection
Convection is the transfer of heat energy through a moving fluid medium (i.e.,
air, water). It can be categorised into two forms: natural and forced. Natural
convection occurs when a heat source (e.g., sun) influences temperature gradients of
a fluid (e.g., air), which in turn sees uneven changes in the densities of the fluid,
causing convection currents to form (e.g., wind; Gebhart & Pera, 1971). Forced
convection occurs when an external source (e.g., fan) generates fluid motion of the
surrounding medium (e.g., air).
The skin is encapsulated by a thin layer of air, independent of ambient
atmosphere, known as the boundary layer (H. Lewis, Foster, Mullan, Cox, & Clark,
1969). The introduction of forced convection through an external source or human
movement disrupts this layer of air and allows heat energy to be transferred from the
skin into the environment; depending upon the velocity of the air, surface area of the
body and the temperature gradient between the skin and the ambient air (Mora-
Rodriguez, Del Coso, Aguado-Jimenez, & Estevez, 2007). As Tc increases
circulatory responses transport warm blood from the core to the periphery,
facilitating the loss of heat at the skin surface via convection.
Evaporation
As Tc rises, or in the presence of rising localised 𝑇sk, the autonomic nervous
system stimulates endocrine sweat glands to secrete sweat along the skin surface
(Nadel, Mitchell, & Stolwijk, 1973). This response allows the release of heat energy
through the diffusion of sweat from the skin surface, in addition to water vapour as a
by-product from respiratory breathing (Mora-Rodriguez et al., 2007). The
effectiveness of this evaporative heat loss is proportionate to the water pressure
gradient between the skin and the environment (i.e., relative humidity), the amount
10 Chapter 2: Literature Review
of moisture present on the skin surface and the convection immediately adjacent to
the skin (Wenger, 1972). The wiping away or dripping of sweat should be avoided
where possible, as it provides no evaporative cooling yet contributes to total body
water losses.
Radiation
Thermal radiation is the electromagnetic radiation emitted by all particles with
a temperature greater than absolute zero; with higher temperatures corresponding to
greater radiation emission (Jones, 1998). Emissivity is the term used to describe the
amount of absolute radiation energy released from an object’s surface relative to an
ideal black body (E. Ng, 2009). By knowing the emissivity coefficient of an object’s
surface, infrared devices are able to detect the object’s surface temperature, which is
a product of the energy being released by the object (Modest, 2013). This concept
will be discussed in greater detail in the subsequent sections (see 2.7.3 Infrared
Devices).
2.4 THERMOREGULATION AND SKIN TEMPERATURE
Healthy thermoregulation in humans requires heat balance to be maintained
through the control of physiological mechanisms (sweating, shivering,
vasoconstriction and vasodilation) that balance heat produced within the body and
heat transfer with the environment. Exercise and/or exposure to a colder/hotter
environment disrupt heat balance within the body. Heat balance can be depicted in
the following equation (International Organisation for Standardisation, 2004a):
M - W = Cres + Eres + K + C + R + E + S
where M equals metabolic rate, W is the effective mechanical power ; Cres and
Eres are the convective and evaporative heat exchanges from breathing; K, C, R and E
are the heat exchanges at the skin by conduction, convection, radiation and
evaporation respectively, and S is the remaining heat storage accumulating in the
body.
2.4.1 Rest
At rest, in thermoneutral conditions, metabolic energy production must equal
the heat loss to the surrounding environment to prevent an elevation in Tc. Up to 70%
of the energy used in human metabolism is lost as heat energy, which at rest equates
Chapter 2: Literature Review 11
to approximately 5 Kcal·min-1 (Sawka & Wenger, 1988). During exercise, this heat
energy produced as a by-product of metabolism can increase up to 20 times (Nadel,
Wenger, Roberts, Stolwijk, & Cafarelli, 1977). Temperature receptors located within
the hypothalamus, spinal cord, skin and some abdominal organs monitor temperature
changes, and work on a negative feedback loop to initiate heat lose through
endocrine sweat activation or blood vessel control (vasodilation) (Cabanac, 1975).
Consequently, 𝑇sk is the cumulative total of a number of factors such as the blood
flow at the surface of the skin, heat conduction from deeper tissues, including
muscle, heat loss from evaporation along the skin as well as the influence of any
environmental thermal loads (Prek & Butala, 2010). Under resting conditions, 𝑇sk
distribution across the body sees cooler temperatures at the extremities in comparison
to more proximal sites (e.g., chest); with differences greatest in colder conditions and
a more uniform distribution in hotter ambient temperatures (Webb, 1992). The
autonomic responses and physiology behind thermoregulation during exercise or
extreme environments is outlined in the following sections.
2.4.2 Exercise
During exercise the body produces a rise in metabolic activity and therefore
thermal energy. In response, thermoregulatory mechanisms of heat loss are enacted
to dissipate this excess heat from the body. Even in extreme environmental
conditions the body is able to maintain this thermal equilibrium for long periods of
time, known as compensable heat loss. If the body’s ability to lose heat through the
skin surface is impaired, via excessive clothing, high relative humidity and/or high
ambient temperatures, heat generation during exercise sees a continual rise in Tc (i.e.,
hyperthermia). When evaporation, convection and conduction are unable to match
heat gain, the potential for heat illness and injury rises (Kulka & Kenney, 2002). This
unsustainable shift in heat balance is referred to as uncompensable heat stress.
Exertional heat stroke occurs when Tc exceeds 40 °C, accompanied with central
nervous system dysfunction (Binkley, Beckett, Casa, Kleiner, & Plummer, 2002). If
not treated correctly the resultant heat stroke can progress from disorientation and
irritability, vomiting and diarrhoea, to loss of consciousness, and in severe cases even
death (Bouchama & Knochel, 2002).
Heat illness in sport has led to player deaths in the National Football League,
competitive marathon running, US collegiate and high school sports (Maron, Doerer,
12 Chapter 2: Literature Review
Haas, Tierney, & Mueller, 2009; Mathews et al., 2012; Mueller & Colgate, 2013).
Currently heat stress is the leading cause of sudden death in US high school athletes
(Kerr, Casa, Marshall, & Comstock, 2013; Mueller & Cantu, 2010), and the greatest
external cause of sudden death in US collegiate and high school athletes (Maron et
al., 2009); American Football has greater than ten times the risk of heat illness than
the average rate of all other sports (Kerr et al., 2013; Yard et al., 2010) and has led to
133 deaths in American Footballers between 1931 and 2012 (Mueller & Colgate,
2013). This has been attributed to the increased metabolic production from wearing
protective equipment in addition to impairing heat loss capacity across the skin
surface causing uncompensable heat gain (Kulka & Kenney, 2002).
During compensable steady state endurance exercise, metabolic heat
production as a bi-product of skeletal muscle contraction sees rapid increases in Tc,
before smaller rates of change form a steady plateau, signalling thermal balance. This
Tc elevation is independent of environmental surroundings and proportional to
metabolic rate within an ambient temperature range of 10 to 35 °C (Lind, 1963; M.
Nielsen, 1938). In contrast, initial increases in 𝑇sk while exercising in the heat are
predominantly a function of ambient temperature and are not significantly dependent
upon workload (Stolwijk & Hardy, 1966). Moreover, 𝑇sk increases in response to
warm environments (~30 °C) are governed by increases in vascular blood flow, and
lag behind Tc changes in order to facilitate heat conductive loss between the hotter
core compartments to the cooler skin (Lim et al., 2008). The Tc to mean skin
temperature (𝑇�sk) gradient (Tc - 𝑇�sk) is a reflection of the body’s conductive rate – the
ability transfer heat via blood from the core to the skin. As 𝑇�sk increases, autonomic
activation of sweat response sees linear increases in evaporative cooling at the skin
(Gagge & Gonzalez, 1996). Consequently, this evaporative heat loss at the skin is
closely associated with the skin’s thermal conductance. Skin thermal conductance
(KSK) equates to the net metabolic heat loss from the skin (HSK) divided by the core to
skin temperature gradient (Tc - 𝑇�sk); represented as KSK = HSK / (Tc - 𝑇�sk). Kraning
and Gonzalez (1991) examined thermoregulatory responses, including Tc to 𝑇sk
gradients, during intermittent exercise in the heat (30 °C) under compensable and
uncompensable (encapsulated chemical suits) heat stress. Intermittent exercise
comprised of 10-min episodes of walking (4-min), running (2-min) and seated rest (4
min). In both groups, were greatest during running and lowest during rest. However,
Chapter 2: Literature Review 13
a notable reduction in the Tc - 𝑇�sk gradient and therefore heat loss capacity, was seen
during uncompensable heat stress compared to compensable. This was reflected in
higher 𝑇�sk as a result of encapsulating clothing which impaired the rate of heat
transfer via conduction from the core to the skin.
2.4.3 Extreme Environments
Similar to exercise induced heat gain, hot environments alone initiate anterior
hypothalamus control of nerve impulses to activate blood vessel vasodilation and
sweating responses to remove excess body heat (Rowell, 2011). This vascular and
sweating reaction can also be activated at localised sites detecting 𝑇sk increase (e.g.,
application of a heat pack; Nadel, Bullard, & Stolwijk, 1971; Randall, 1946).
Overall, fluctuations in Tc tend to have greater influence on autonomic responses to
maintain heat balance than that of 𝑇sk (Simon, Pierau, & Taylor, 1986). However,
thermal comfort within an environment and therefore behavioural thermoregulation,
have been shown to be heavily influenced by 𝑇sk (Frank, Raja, Bulcao, & Goldstein,
1999). Changes in surrounding ambient conditions are detected more readily by skin
thermoreceptors that serve to initiate behavioural responses such as seeking warmth,
prior to the recruitment of more metabolically costly reactions (i.e., shivering). The
activity of nerve fibres responding to cold, cold-pain, heat and heat-pain along the
skin surface are published in Guyton and Hall (2000) (Figure 48-10).
In fluctuating environmental temperatures the skin is more responsive to
changes towards colder temperatures due to as many as 10 times the amount of cold-
sensitive nerve endings (Guyton & Hall, 2000). Cold-sensitive temperature signals
originating from thermoreceptors converge while ascending through the spinal cord,
before diverging to multiple brain areas including the midbrain raphe nuclei, reticular
formation and posterior hypothalamus (Burstein, Cliffer, & Giesler, 1987). The
responses evoked (i.e., shivering and vasodilation) are dependent on the amount and
location of cooling, the baseline 𝑇sk and the sum area of the cooled skin (Van
Someren, Raymann, Scherder, Daanen, & Swaab, 2002). Sympathetic stimulation
prompts vasoconstriction of blood vessels to direct blood supply away from the skin,
reducing heat loss into the environment. Concomitant to this, if required – primarily
via Tc changes – hormonal messengers (i.e., norepinephrine) are released from the
medulla to commence involuntary muscle shivering to produce additional metabolic
14 Chapter 2: Literature Review
heat (Cheng et al., 1995). During prolonged cold stress intermittent vasodilation of
extremities, such as the hands, increases blood flow and subsequent 𝑇sk of the finger
tips, which is then followed by another period of vasoconstriction. This process is
repeated and is known as ‘the hunting reaction’ (T. Lewis, 1930) or cold induced
vasodilation (Flouris & Cheung, 2009). The exact reasons for this reaction occurring
are unknown. However, it has been proposed that the increased temperature due to
vasodilation helps reduce cold-related injury (i.e., frostbite; Wilson & Goldman,
1970) and/or maintain manual dexterity and tactile sensitivity (Daanen, 2003).
Variables which make up the surrounding environment such as air temperature,
radiant temperature, wind speed and relative humidity influence the effectiveness of
heat loss mechanisms (i.e., conduction, evaporation etc.) employed by the human
body and as a result can disrupt heat balance of an individual. For the purpose of this
literature review, particular attention will be paid to the influence of hot
environments on human heat exchange.
High ambient temperatures alter the thermal gradient between the skin and the
environment. Once ambient temperatures exceed that of 𝑇sk, conductive and
convective cooling of the skin no longer is achievable, resulting in the ambient
conditions imposing conductive and convective heating of the skin (Prek & Butala,
2010). Similarly, environmental heat gain will progress if radiant temperatures of
surrounding objects exceed 𝑇sk. Thermoregulatory processes overcome this obstacle
by initiating a sweating response to dissipate heat through unidirectional evaporative
cooling. However, evaporative cooling is inversely related to the level of water
vapour (humidity) in the air at a given ambient temperature. In a hot environment,
evaporation plays an important role in dissipating excess body heat, as smaller
differences between the skin and ambient air blunt the heat exchange from
convective and radiative means (Prek & Butala, 2010). Where ambient temperatures
exceed 𝑇sk, cutaneous and respiratory evaporation can account for >80% of heat loss,
as the human body absorbs conductive and convective heat energy from the
environment (L. Armstrong & Maresh, 1993). If water vapour in the ambient air
continues to rise the evaporative cooling rate would slow. Once relative humidity
reaches 100%, sweat and therefore heat energy does not evaporate from the skin (W.
Kenney, DeGroot, & Alexander Holowatz, 2004).
Chapter 2: Literature Review 15
2.5 MEAN SKIN TEMPERATURE
Due to the difficulties associated with measuring the temperature of the entire
skin surface, 𝑇�sk provides a single temperature value derived from temperatures
taken at various sites in respect to a specific formula. 𝑇�sk formulas typical use
weighting factors corresponding to the contribution a particular site makes to the skin
surface area or thermal sensitivity. Formula differ in the total number of sites
measured and weighting factors given to the site, with some formulas varying
between universal weighting (Burton, 1935; Ramanathan, 1964), variable weighting
(Park et al., 1988; Winslow, Herrington, & Gagge, 1936), or no weighting (Mitchell
& Wyndham, 1969; Stolwijk & Hardy, 1966). An explanation of a general formula
for 𝑇�sk is represented below:
𝑇�sk = (ω1·T1) + (ω2·T2) + … + (ωn·Tn)
Where T represents the measured temperature at a given site; ω is the formula
weighting factor. Numerous formulas have been established to estimate 𝑇�sk, ranging
from 3 (Burton, 1935) to 15 (Mitchell & Wyndham, 1969) measurement sites (Table
2.1). 𝑇�sk is predominantly used in exercise science applications, and when coupled
with other physiological measures of exercise such as heart rate and core body
temperature, an evaluation of physiological strain and whole body temperature can
be made (Colin, Timbal, Houdas, Boutelier, & Guieu, 1971; Cuddy et al., 2013).
16 Chapter 2: Literature Review
Table 2.1.
Commonly used 𝑇�sk formula, including site and weighting.
Region Head Trunk Upper Arm Forearm Hand Thigh Calf Foot
Formula Sites Forehead Cheek Neck Chest Abdomen Scapula Sub-scapula Lumbar Posterior Antero-
lower Anterior Posterior Dorsal Anterior Antero-medial
Postero-medial
Postero-lower Anterior Posterior Dorsal
W
Burton[1] 3 0.5 0.14 0.36
Olesen[2] 3 0.5 0.14 0.36
ISO-9886[3] 4 0.28 0.28 0.16 0.28
Ramanathan[4] 4 0.3 0.3 0.2 0.2
Newberg[5] 4 0.34 0.15 0.33 0.18
Houdas[5] 5 0.07 0.175 0.175 0.19 0.39 `
Palmes/Park[6] 6 0.14 0.19 0.19 0.11 0.05 0.32
Hardy/DuBois[7] 7 0.07 0.35 0.14 0.05 0.19 0.13 0.07
Gagge/Nishi[8] 8 0.07 0.175 0.175 0.07 0.07 0.05 0.19 0.2
Nadel[9] 8 0.21 0.1 0.17 0.11 0.12 0.06 0.15 0.08
Crawshaw[11] 8 0.19 0.08 0.12 0.09 0.13 0.12 0.12 0.15
Houdas/Colin[5] 10 0.2 0.05 0.125 0.2 0.05 0.05 0.05 0.125 0.075 0.075
Colin/Houdas[5] 10 0.06 0.12 0.12 0.12 0.08 0.06 0.05 0.19 0.13 0.07
Mitchell[6] 10 0.1 0.125 0.125 0.07 0.07 0.06 0.125 0.125 0.15 0.05
Hardy/DuBois[6] 12 0.07 0.0875 0.0875 0.0875 0.0875 0.14 0.05 0.095 0.095 0.065 0.065 0.07
UW
Stolwijk[11] 10 1/10 1/10 1/10 1/10 1/10 1/10 1/10 1/10 1/10 1/10
Mitchell[6] 15 1/15 1/15 1/15 1/15 1/15 1/15 1/15 1/15 1/15 1/15 1/15 1/15 1/15 1/15 1/15
W = weighted formula; UW = unweighted formula; ISO = International Organisation for Standardisation. [1] = (Burton, 1935); [2] = (Olesen, 1984); [3] = (International Organisation for Standardisation, 2004b); [4] = (Ramanathan, 1964); [5] = (Houdas & Ring, 1982); [6] = (Mitchell & Wyndham, 1969); [7] = (Hardy et al., 1938); [8] = (Gagge & Nishi, 1977); [9] = (Nadel et al., 1973); [10] = (Crawshaw, Nadel, Stolwijk, & Stamford, 1975); [11] = (Stolwijk & Hardy, 1966)
Chapter 2: Literature Review 17
2.6 APPLICATIONS OF SKIN TEMPERATURE MEASUREMENT
Even before the invention of temperature measurement instruments, the
relationship between localised human temperature and pathologies were identified.
As early as 400 BC, the first documented cases of temperature-related conditions
such as fever, involved subjective diagnosis through touching the skin to identify any
temperature differences (Tan, Ng, Rajendra Acharya, & Chee, 2009). In 1868, Carl
Wunderlich invented the clinical thermometer (Ring, 2007). This led the way for the
invention of modern adaptations currently used to assess of human temperature
throughout medicine, exercise science, occupational and research settings.
Exercise Science
Despite substantial research into the larger field of whole-body
thermophysiology, rates of reported thermal illness and injury are on the rise
(Nelson, Collins, Comstock, & McKenzie, 2011). Between 1997 and 2006, an
estimated 54,983 patients were treated for heat-related injury and illness by United
States emergency departments (Nelson et al., 2011). A worrying trend was noted
with the heat injury-illness rates per 100,000 people more than doubling between
1997 (1.2) to 2006 (2.5); with over three-quarters of incidents during this period a
result of participation in sport or exercise. As a result, 𝑇sk is of interest in exercise
and sports medicine as it provides insight into the relationship between the human
body and the surrounding environment. The most popular use of 𝑇sk in exercise
science is the use of 𝑇�sk as an important outcome variable during exercise or testing
in extreme environments. 𝑇sk has been used as the primary measurement outcome in
recent novel exercise science investigations in the identification of delayed onset
muscle soreness (Al-Nakhli, Petrofsky, Laymon, & Berk, 2012) and the
quantification of aerobic and functional performance (Al-Nakhli, Petrofsky, Laymon,
Arai, et al., 2012; Bleakley et al., 2012; Sawka, Cheuvront, & Kenefick, 2012).
Another important application of 𝑇sk assessment in exercise science is during
cryotherapy, or therapeutic tissue cooling. Cryotherapy has become a popular
modality for athletes to improve recovery times following exercise (Costello,
McInerney, Bleakley, Selfe, & Donnelly, 2012), and can be implemented through a
variety of techniques including, but not limited to, cold water immersion, cold air
and ice packs. It has been proposed that a reduction in tissue temperature of at least
18 Chapter 2: Literature Review
12 °C is needed before cryotherapy provides any analgesic effect (Bleakley &
Hopkins, 2010). However, no safe lower limit for 𝑇sk has been established resulting
in reported cases of cold rash (Dover, Borsa, & McDonald, 2004), ice burn (Selfe,
Hardaker, Whitaker, & Hayes, 2007) and nerve damage (Moeller, Monroe, &
McKeag, 1997). These potential risks associated with tissue cooling has seen thermal
imaging become the preferred 𝑇sk measure, because of its superior data collection
across the entire area of interest compared to the spot measurements of more
traditional contact devices (Hardaker et al., 2007).
Occupational
Occupational settings that present high thermal loads run the risk of decreased
productivity and employee safety. Therefore, the standardisation of safety limits for
the maximum physiological temperatures of core and skin have been set to 39.5 and
43 °C respectively (International Organisation for Standardisation, 2004b). Industries
with the greatest risks of exposing workers to high thermal loads include
manufacturing (Fogleman, Fakhrzadeh, & Bernard, 2005), agriculture (Jackson &
Rosenberg, 2010), mining (Hunt, Parker, & Stewart, 2012), emergency services
(Bourlai, Pryor, Suyama, Reis, & Hostler, 2012), construction (Lundgren, Kuklane,
Gao, & Holmer, 2013) and participation in the armed forces (Carter III et al., 2005).
Further to this, studies observing manufacturing injury rates have reported a
significantly greater number of injuries when workplace temperatures exceed 32 °C
(Fogleman et al., 2005) and 42 °C (Nag & Nag, 2001).
In Australia, the cost of work-place injuries and illness as a result of exposure
to Heat, Radiation or Electricity during 2008-2009 in Australia was estimated to be
$1.3 billion (Safe Work Australia, 2012). Studies implementing physiological
measures such as Tc and 𝑇sk assessment have developed and advocated successful
strategies to be implemented in workplaces to help reduce the risks of heat illness
and injury including; self-pacing (Brake & Bates, 2002; Gun & Budd, 1995), work-
rest cycles (Mairiaux & Malchaire, 1985), employee hydration education (Brake &
Bates, 2003) and safety standards for environmental conditions (International
Organisation for Standardisation, 2004a).
In cold environments, the estimated required clothing ensemble and the
corresponding thermal insulation needed for safe exposure times at a given
temperature and wind speed are standardised in ISO 11079 (International
Chapter 2: Literature Review 19
Organisation for Standardisation, 2007). Those recommendations are provided to
maintain homeostatic Tc and 𝑇sk. If clothing is inadequate, the criteria for cessation
of cold exposure in the workplace has been set at a 3 °C fall in 𝑇�sk below
comfortable thermoneutral levels (𝑇�sk ≈34 °C; International Organisation for
Standardisation, 2007, 2009). Localised 𝑇sk limits have been addressed in ISO 11079
(International Organisation for Standardisation, 2007), which recommends the
wearing of gloves and regular monitoring of finger temperatures in cold workplaces
to ensure temperature limits >24 °C are preserved to allow for adequate hand
function. Falls below this finger 𝑇sk could see a loss in dexterity, strength and
coordination increasing the risk for incidence and injury. Further information
regarding the predicted time requirements for the development of pain, numbness
and frostbite as a result of conductive heat loss by touching various materials at a
range of temperatures can be found in ISO 13732/3 (International Organisation for
Standardisation, 2005).
Research has also been conducted into the ergonomic environment of office
workers and associated risks of overuse injury. Gold, Cherniack, and Buchholz
(2004) successfully detected 𝑇sk reductions in the hand following a nine-minute
typing exercise in office workers, potentially leading to a more effective way of
detecting the onset of overuse injuries such as tendinitis and carpal tunnel through
the presence of oedema, inflammation and associated heat.
Clinical
The measurement of 𝑇sk is particularly valuable in the screening, prevention
and diagnosis of various pathologies in unhealthy populations. In clinical settings,
𝑇sk examination has a wide range of applications including breast cancer detection,
diabetic neuropathy and vascular disorders, ocular diseases, dental diagnosis,
inflammatory and osteo-arthritis monitoring. Recent reviews by Ring and Ammer
(2012) and Lahiri and colleges (2012) provide a thorough overview of use of 𝑇sk
measurement in a clinical setting.
Public Health
In the wake of sever acute respiratory syndrome (SARS), swine influenza and
other infections pandemic fevers, non-contact infrared techniques have been widely
used by government health organisations to screen large populations for signs of
20 Chapter 2: Literature Review
fever by measuring face and neck temperatures (Ring & Ammer, 2012). In some
cases this screening measure has been shown to be an effective tool for fast and non-
contact mass screening of fever (Chiang et al., 2008; Chiu et al., 2005; Nguyen et al.,
2010). However, there has been a documented failure of infrared cameras to
successfully identify febrile individuals because of influences by a large number of
individual and environmental factors; such as perspiration, cosmetic make-up, wind
drafts, ambient temperatures and subject to sensor distance (Bitar, Goubar, &
Desenclos, 2009; Ring & Ammer, 2012). This has led to some authors to suggest that
infrared screening may only serve as an alternative Tc measurement tool (Chan,
Cheung, Lauder, & Kumana, 2004) or should be replaced by conductive measures
(Liu, Chang, & Chang, 2004). Regardless, the International Organisation for
Standardisation has developed a set of international standards to help enable the
reliable and reproducible use of infrared cameras for mass screening of fever
(International Organisation for Standardisation, 2007).
2.7 CHARACTERISTICS THAT INFLUENCE HUMAN SKIN TEMPERATURE
Human 𝑇sk is a dynamic physiological response to the surrounding
environment. There are however other inherent and behavioural characteristics that
influence an individual’s 𝑇sk. Where possible these factors should be controlled for
the accurate and reliable measurement of human 𝑇sk. The following section will
outline a number of these characteristics which can be divided into two sub-groups:
1) Inherent – personal characteristics in which there is little or no control over;
and
2) Behavioural – habitual and behavioural factors that can be altered.
2.7.1 Inherent
When evaluating 𝑇sk, intrinsic biological and anatomical factors need to be
taken into consideration. It is impossible to control many of these inherent
characteristics, though it is important to understand their effects on 𝑇sk.
Sex
Many thermophysiology studies avoid recruiting female participants due to
temperature fluctuations associated physical and hormonal differences when
compared to men (Kaciuba-Uscilko & Grucza, 2001). Sexual dimorphism of
Chapter 2: Literature Review 21
anthropometrical characteristics has been cited for thermoregulatory and 𝑇sk
differences between males and females. In cold conditions, female 𝑇�sk is up to 0.5 °C
lower than that of male counterparts (McArdle, Toner, Magel, Spinal, & Pandolf,
1992) and up to 0.7 °C lower in hot conditions (Bittel & Henane, 1975); due to larger
body surface to mass ratio, smaller total and lean body mass and a lower resting
metabolic heat production compared to men (Arciero, Goran, & Poehlman, 1993;
Cortright & Koves, 2000). Interestingly, in a study of lean and obese men matched
for subcutaneous and total body fat but differed in body mass and morphology, found
no significant difference in 𝑇sk between groups during 120-min cold water
immersion (18 °C; Glickman-Weiss et al., 1993). These findings suggest that other
factors such as metabolic rate via lean mass differences and hormonal responses have
a greater influence on 𝑇sk between sexes than morphology.
There have been numerous investigations into the influence that hormonal
changes, particularly throughout the menstrual cycle, have on thermoregulatory
processes in females (Hirata et al., 1986; Horvath & Drinkwater, 1982). Tc
fluctuations have been noted in females using oral contraceptives (hotter
temperatures), during the luteal (hotter temperatures) and the follicular phases
(colder temperatures) of menstruation relative to men (see Figure 2 published in - F.
Baker & Driver, 2007). Hotter temperatures during the luteal phase are most likely
mediated by the hormone progesterone (Rothchild & Barnes, 1952) which alter the
output of thermosensitive neurones in the hypothalamus responsible for temperature
regulation (Nakayama, Suzuki, & Ishizuka, 1975).
Female 𝑇sk is lowest during the follicular phase as a result of reductions in
peripheral blood flow in association with lower Tc (Bartelink, Wollersheim,
Theeuwes, Van Duren, & Thien, 1990; Frascarolo, Schutz, & Jequier, 1992;
Hessemer & Bruck, 1985). Despite these findings, in the presence of exercise no
differences in 𝑇sk have been observed between phases (Pivarnik, Marichal, Spillman,
& Morrow, 1992). Pivarnik et al. (1992) found that during 60-min of endurance
cycle ergometry in thermoneutral conditions oxygen uptake, sweat loss and 𝑇sk were
not influenced by cycle phase. However, Tc, cardiovascular strain and perceived
exertion were all adversely affected during the luteal phase. Fluctuations in hormone
levels in pre and post-menopausal women reduces thermoregulatory control of
vasodilation and in turn sees falls in skin blood flow and therefore 𝑇sk (Brooks et al.,
22 Chapter 2: Literature Review
1997; Charkoudian, Stephens, Pirkle, Kosiba, & Johnson, 1999). Oestrogen
supplementation and hormone therapies have been postulated to increase skin blood
flow and 𝑇sk via increased vasodilation of subcutaneous vessels by stimulating nitric
oxide-dependent vasodilation (Charkoudian et al., 1999). Although, numerous
studies into the effectiveness into this treatment have yielded mixed results (Gilligan,
Badar, Panza, Quyyumi, & Cannon, 1994; Sudhir, Esler, Jennings, & Komesaroff,
1997).
Age
Metabolic and circulatory changes associated with increasing age have often
been suggested as causative factors for thermoregulatory reductions (Petrofsky et al.,
2006). Indeed, studies of 𝑇sk in the elderly show comparative differences to younger
participants (Niu et al., 2001). For example, Niu et al. (2001) tested the 𝑇sk of 57
participants, ranging from 20-88 years and found subjects over 60 years old had
lower 𝑇sk than their younger counterparts. These differences were more pronounced
in the extremities and most likely as a result of impaired circulation capacity during
advancing age. Other studies have also observed age-related diminishing of
vasoconstrictive and vasodilative responses of subcutaneous blood vessels as well as
a decline in sympathetic nerve activity (Holowatz & Kenney, 2010; W. Kenney &
Armstrong, 1996). These adaptations are evident in the elderly who have higher rates
of hypothermia during surgery (Vaughan, Vaughan, & Cork, 1981) and take longer
to rewarm following surgery (Frank et al., 1992). Raymann, Swaab, and Van
Someren (2007) have also documented the inverse relationship between age and
physiological measures such as 𝑇sk, Tc, circadian rhythm and sleep-onset latency.
Although normative Tc for various age groups have been identified (Chamberlain,
Terndrup, Alexander, Silverstone, & Wolf-Klein, 1995), there is currently no defined
normative 𝑇sk range for respective age groups. Further research into these ranges
could allow for more accurate comparisons of the literature and help better
understand the relationship between thermoregulatory deficits and age.
Body Composition
Consideration must be given to what effect excess adiposity has on human 𝑇sk.
In an investigation by Frim, Livingstone, Reed, Nolan, and Limmer (1990) it was
indicated that the distribution of subcutaneous fat influenced measurement error
when calculating 𝑇sk, by altering heat transfer between the core and the skin. Obese
Chapter 2: Literature Review 23
individuals have been identified as having a lower 𝑇sk compared to leaner
participants (LeBlanc, 1954; Livingstone, Nolan, Frim, Reed, & Limmer, 1987;
Savastano et al., 2009). These 𝑇sk differences are greatest in cooler ambient
conditions and decrease as ambient temperature rises (Livingstone et al., 1987).
These findings are not totally unexpected given the impaired vasomotor control seen
in obese populations during changes in Tc (Kasai, Hirose, Matsukawa, Takamata, &
Tanaka, 2003; Meyer, Kundt, Steiner, Schuff-Werner, & Kienast, 2006). In addition,
resting metabolic heat production is significantly higher in the obese compared to
lean individuals due to the greater lean mass (i.e., muscle) that accompanies obesity
(Prentice et al., 1986). The insulating characteristics of fat also prevent efficient heat
loss from the skin into the environment. The influences of fat mass are attributed to a
reduction in thermal conductivity between the core and the skin (Cooper & Trezek,
1971; Lipkin & Hardy, 1954) and are proportional to the degree of obesity (P. Baker
& Daniels, 1956; Jéquier, Gygax, Pittet, & Vannotti, 1974). Furthermore, as
cutaneous heat loss, and the resultant 𝑇sk, is proportional to the total skin surface area
(Sessler, McGuire, & Sessler, 1991), than increases in weight (fat gain) without
relative increases in height will see a reduction in the surface area to total body mass
ratio (Verbraecken, Van de Heyning, De Backer, & Van Gaal, 2006). Therefore, any
change in body composition resulting in greater fat-mass promotes the retention of
body heat and slows the rate of metabolic heat loss (Kurz, Sessler, Narzt, Lenhardt,
& Lackner, 1995), which is reflected in cooler cutaneous temperatures where high
amounts of subcutaneous fat is present (Savastano et al., 2009).
Circadian Rhythm
Human sleep regulation is controlled by a biological circadian rhythm that
adjusts a variety of physiological variables over a 24-hour cycle (Hasselberg,
McMahon, & Parker, 2013). Of most importance to sleep/wake researchers is the
accurate measurement of diurnal oscillation of Tc and 𝑇sk. Independent of exercise Tc
can fluctuate within a range of 1.3 °C in young men (Vitiello et al., 1986) with
amplitudes as low as 0.7 °C depending on age (Rosenthal et al., 1990). Moreover,
because heat loss at the skin is directly related to changes in Tc, 𝑇sk has been shown
to be a reliable measure of circadian system status (Sarabia, Rol, Mendiola, &
Madrid, 2008). The absolute 𝑇sk changes over a daily cycle vary between the
different regions of the body being measured (Krauchi & Wirz-Justice, 1994).
24 Chapter 2: Literature Review
Furthermore, Krauchi and Wirz-Justice (1994) found that proximal body regions
such as the chest, thigh and forehead reflected the same relative temperature changes
to that of Tc, while more distal sites such as the hand and feet have an inverse
relationship with Tc rhythms. Particular interest has been given to these temperature
gradients between distal and proximal 𝑇sk sites as a predictor of sleep propensity
(Hasselberg et al., 2013; van Marken Lichtenbelt et al., 2006).
The endogenous changes in Tc throughout a given day, has led some
researchers to consider the optimal times for heat load management during exercise.
More specifically, it has been proposed that circadian rhythm prevents optimal
removal of heat loads at the skin during exercise in the early morning hours, and that
optimal heat loss occurs in the late afternoon (Aldemir et al., 2000; Arnett, 2002).
This is a result of Tc being lowest during the early morning just before awakening
which coincides with the body initiating a ‘heat gain’ phase (Krauchi & Wirz-Justice,
1994). The opposite can be said for late afternoon at the time of highest body
temperatures and the initiation of a more efficient ‘heat loss’ phase in the hours
leading up to sleep onset (Krauchi & Wirz-Justice, 1994).
Dominance, Asymmetry and Pathophysiology
In a novel investigation, Gross, Schuch, Huber, Scoggins, and Sullivan (1988)
observed both men and women found that dominance has no effect on contralateral
𝑇sk measurements at both the wrist and the knee. However, comparative studies have
used skin thermography to measure temperature differences between limbs, or
temperature thresholds at specific sites to aid in the diagnosis of illnesses and injury
(Table 2.2).
Chapter 2: Literature Review 25
Table 2.2.
Examples of 𝑇sk changes used to aid in the diagnosis of illness and injury.
Author Pathology Identified Temperature
Wasner et al. (2002) CPRS I Asymmetries >2.1 °C
D. Armstrong, Lavery, Liswood, Todd, and Tredwell (1997) Diabetic Foot Ulcer Asymmetries >3.1 °C
Lavery et al. (2007) Diabetic Foot Ulcer Asymmetries >2.2 °C
Chiu et al. (2005) Fever Forehead >38 °C
Hausfater, Zhao, Defrenne, Bonnet, and Riou (2008) Fever Forehead >37.5 °C
Ring et al. (2008) Fever (Children) Forehead >36.9 °C
Hildebrandt, Raschner, and Ammer (2010) Overuse Knee Injury Asymmetries >1.4 °C
Ben-Eliyahu (1991) PFPS Asymmetries >1 °C
Davidson and Bass (1979) PFPS Asymmetries >0.5 °C
Mayr (1995) Post-operative knee surgery
Abnormal asymmetries >0.5 °C
Spalding et al. (2008) Rheumatoid Arthritis HDI >1.3 °C
Goodman, Heaslet, Pagliano, and Rubin (1985) Tibial Stress Fractures Asymmetries >0.5 °C
CPRS I: Chronic regional pain syndrome (nerve disorder); PFPS: Patellofemoral pain syndrome; HDI:
Heat distribution index.
In healthy subjects, normative healthy asymmetrical 𝑇sk differences between
sites have been reported to be as low as 0.25 °C (Uematsu, 1985a; Vardasca, 2008).
Comparative studies into bilateral differences within individuals have been
commonly used to detect the presence of a variety of pathologies (D. Armstrong et
al., 1997; Feldman & Nickoloff, 1984; Mayr, 1995; Uematsu, 1985b; Wasner et al.,
2002). These studies typically measure 𝑇sk with IC’s because of its superior data
collection and complete topography of the areas of interest (Costello, Stewart, Selfe,
Karki, & Donnelly, 2013). Overall, skin thermography is commonly used as a
diagnostic criteria in the identification and treatment of overuse and soft tissue
injuries (Ben-Eliyahu, 1991; Bouzida et al., 2009; Davidson & Bass, 1979; Goodman
et al., 1985; Hildebrandt et al., 2010; Mayr, 1995), influenza screening (Chiu et al.,
2005; Hausfater et al., 2008; Ring et al., 2008), malignant tumours (Arora et al.,
2008; Herman & Cetingul, 2011), autoimmune and nervous system diseases (D.
26 Chapter 2: Literature Review
Armstrong et al., 1997; Lavery et al., 2007; Spalding et al., 2008; Wasner et al.,
2002).
Medications
Thermoregulatory responses, including 𝑇sk, have been used to evaluate the
effects of various medications such as analgesics, anti-inflammatories, vasoactives
and hormonal treatments (Ring, Engel, & Page-Thomas, 1984). In order to control
for potential thermoregulatory changes in participants on various medication, a
number of investigations have excluded participants currently taking medications
(Pascoe, Barberio, Elmer, & Wolfe, 2012; Ring & Ammer, 2000; Zaproudina,
Airaksinen, & Närhi, 2013; Zaproudina, Varmavuo, Airaksinen, & Närhi, 2008).
This logical approach is used despite no defined list of medications that influence
human thermoregulation or a standardised pre-examination screening of a patient’s
medication history. Currently, only one international standard (ASTM-E1965, 1998)
states that subjects should be excluded from measurement if an individual has used
“…medications known to affect body temperature (for example, antipyretics,
barbiturates, thyroid preparations, antipsychotics, etc.) within 3 h of the test, or
immunization within seven days of the test.” However, this recommendation is in
relation to tympanic Tc measurements taken with an infrared thermometer. Future
amendments to international standards should not overlook the potential for
erroneous 𝑇sk values, as a result of even commonly used medications such as
paracetamol, aspirin, ibuprofen and oral contraceptives.
2.7.2 Behavioural
Caffeine, Nicotine & Ethanol (Alcohol)
At present, the literature pertaining to the effect caffeine has on 𝑇sk is
contradictory – with increases (Koot & Deurenberg, 1995), decreases (Quinlan et al.,
2000) and no change reported (Daniels, Molé, Shaffrath, & Stebbins, 1998)
following consumption. Two studies have found attenuated 𝑇sk increases in
participants who have consumed hot coffee, compared to a hot water control group.
This response suggests caffeine has a vasocontrictive effect on peripheral blood
vessels (Quinlan, Lane, & Aspinall, 1997; Quinlan et al., 2000). Concomitantly, a
dose response was found between the attenuated 𝑇sk rises and greater caffeine
consumption (Quinlan et al., 2000). The authors attributed these increases in 𝑇sk to
caffeine’s pressor effects as a result of adenosine receptor antagonism. Because
Chapter 2: Literature Review 27
caffeine molecules closely resemble the chemical adenosine, it is thought caffeine
blocks A1, A2A and A2B receptors in blood vessels, thereby acting as an antagonist
and decreasing cutaneous blood flow (Namdar et al., 2009). However, subsequent
research into the pressor mediator as a result of caffeine consumption found
increases were still present in decaffeinated coffee (Corti et al., 2002). This
conclusion suggests another factor within hot coffee, and not the caffeine itself,
initiates vasoconstriction and weakened 𝑇sk rises. The potential inconsistencies
between the aforementioned caffeine and 𝑇sk studies may be due to the administering
of the caffeine through hot beverages that alter vasomotor mechanisms (Koot &
Deurenberg, 1995; Quinlan et al., 2000) compared to an ingestible gel capsule
(Daniels et al., 1998).
Nicotine intake via cigarettes initiates subcutaneous vasoconstriction and
resultant 𝑇sk reductions in smokers by up to 7 °C (Sørensen et al., 2009; Weatherby,
1942; West & Russell, 1987). These acute changes in 𝑇sk can last up to 90-min after
smoking (Gershon-Cohen, Borden, & Hermel, 1969; Gershon-Cohen & Habennan,
1968). There is some inconsistency in the literature with one author reporting 𝑇sk
increases as a result of acute nicotine ingestion (Usuki, Kanekura, Aradono, &
Kanzaki, 1998). However, participants in this study chewed nicotine gum and did not
smoke a cigarette like in the previous investigations (Gershon-Cohen et al., 1969;
Gershon-Cohen & Habennan, 1968; Weatherby, 1942; West & Russell, 1987). The
chronic effects of smoking also alter thermoregulation through the narrowing of
blood vessels, potentially leading to health complications such as peripheral vascular
disease which reduces distal 𝑇sk (Huang et al., 2011).
Conversely, alcohol ingestion causes dilation of blood vessels thus increasing
𝑇sk (Ammer, Melnizky, & Rathkolb, 2003; Wolf, Tüzün, & Tüzün, 1999). Detailed
investigations regarding the influence of alcohol on 𝑇sk have shown a multifaceted
relationship between the two depending on other variables. For example, influences
are dependent on ethnicity (Harada, Agarwal, & Goedde, 1981), the increases in 𝑇sk
are amplified on an empty stomach (Mannara, Salvatori, & Pizzuti, 1993) or with
greater alcohol consumption (Finch, Copeland, Leahey, & Johnston, 1988); and the
increases are attenuated in ambient temperatures outside of 20 and 35 °C (Hughes,
Henry, & Daly, 1984; Risbo, Hagelsten, & Jessen, 1981) or if an individual
participates in habitual alcohol consumption (Mannara et al., 1993).
28 Chapter 2: Literature Review
In summary, there is a wide range of conflicting evidence between the
direction and magnitude of temperature effects following the consumption of
caffeine, nicotine and alcohol. Researchers and clinicians should be aware that in any
case, influences are present after ingestion of these socially acceptable drugs and
should be controlled for when requiring accurate and reliable 𝑇sk measurements.
Food
There is a consensus within the literature that 𝑇sk increase as a result of food
intake, referred to as diet-induced thermogenesis (Dauncey, Haseler, Thomas, &
Parr, 1983; Shuran & Nelson, 1991; Westerterp-Plantenga, Wouters, & Ten Hoor,
1990). The thermic effect of feeding sees a rise in metabolic rate and oxygen
consumption causing a concomitant increase in body temperature (Rothwell & Stock,
1983). 𝑇sk increases tend to peak 90-min following eating and can take up to 3 hours
before a return to baseline levels depending on the skin site (Dauncey et al., 1983;
Westerterp-Plantenga et al., 1990).
Beverages
The influence of hydration status on Tc has been well defined (Sawka & Coyle,
1999; Sawka et al., 1998) with 𝑇sk largely overlooked. These studies note that during
endurance exercise dehydration blunts the thermoregulatory pathways that dissipate
heat loads. To counter these detrimental effects on performance, subsequent studies
have used ice slurry mixtures in an attempt to precool runners (Lee, Shirreffs, &
Maughan, 2008; Siegel et al., 2010; Siegel, Maté, Watson, Nosaka, & Laursen,
2012). In an investigation by Siegel et al. (2010) 𝑇�sk was reduced under resting
conditions following either cold water or ice slurry ingestion, with significant
differences between groups. Surprisingly, two other studies comparing the effect of
warm water and cold (Lee et al., 2008) or ice water (Siegel et al., 2012) during rest
and exercise and found no significant effect between water temperature and 𝑇�sk
during resting conditions. Unfortunately, neither study implemented a control group
that had no fluid, to see if the fluid itself and subsequent hydration status, regardless
of temperature, altered 𝑇�sk. Also, it may have been more beneficial to measure 𝑇sk
changes at individual sites. 𝑇�sk calculated from central and peripheral sites may have
prevented significant differences to be detected, as central 𝑇sk sites are less sensitive
to temperature changes than distal regions (Merla, Mattei, Di Donato, & Romani,
2010). Another study has reported the effect of sparkling water intake on 𝑇sk
Chapter 2: Literature Review 29
(Ammer et al., 2003). The purpose of this study was to measure 𝑇sk in the hand,
knees and face during alcohol consumption. Surprisingly, the control group reported
significant 𝑇sk falls after consuming only sparkling water. Falls of up to 0.9 °C were
reported in the control group, though it was not clear if these changes could be a
result of the carbonic acid present in the sparkling water.
Exercise Performance and Acclimatisation
Training status and environmental acclimatisation influence the
thermoregulatory response and therefore 𝑇sk during exercise. For example the trained
have been shown to have higher resting and exercising 𝑇sk as a result of increase skin
blood flow compared to the untrained (Fritzsche & Coyle, 2000; Liu et al., 2004).
While the untrained have an impaired cooling capacity during exercise and a slower
𝑇sk recovery back to baseline (Merla et al., 2010). These same thermoregulatory
responses are present in populations that are acclimatised to the heat when compared
to the unacclimatised (Sawka, Wenger, & Pandolf, 2010).
Ambient temperature has also been shown to influence the work rate of
participants during self-paced exercise in the heat. (Tucker, Marle, Lambert, &
Noakes, 2006) examined the effect of exercise in the heat on pacing strategies on
eight cyclists and found that exercise in the heat (35 °C) saw significantly less
power-output and slower self-pacing when compared to normal (25 °C) or cool (15
°C) temperatures. As there were no significant differences in Tc or heat storage seen
between conditions, this response in altered self-paced exercise intensity was
attributed to the sympathetic feedback of thermoreceptors in located in the skin to
ensure thermal homeostasis is maintained.
2.8 SKIN TEMPERATURE MEASUREMENT TECHNIQUES
Means in which 𝑇sk can be acquired could be placed into two categories (1)
conductive and (2) infrared with each method having its own innate advantages and
limitations. The following sections will describe in detail the most commonly used
instruments for 𝑇sk assessment. A systematic review outlining the interchangeability
between conductive and infrared devices is presented in Chapter 3.
30 Chapter 2: Literature Review
2.8.1 Conductive Devices
Conductive devices are based upon the transfer of heat energy into the device
through direct contact with the object of interest (discussed earlier in section
Thermodynamics). There are a wide variety of types, makes and models of
commercially available conductive devices. For the purpose of this review three of
the most popular types of devices will be introduced. Thermocouples (TC),
Thermistors (TM) and iButtons® (IB) are typical contact measures of 𝑇sk that have
been viewed as advantageous by clinicians due to the relatively low cost and the
associated ease of use (Tyler, 2011).
Thermocouples
TC function as a result of an interaction known as the Seebeck effect; where by
the temperature measured is proportional to the voltage between the probes of two
dissimilar metals when in the presence of a temperature gradient (Klopfenstein,
1994). In order to measure and record temperatures of interest, the TC’s must be
plugged into an associated data logger. Thermocouples are advantageous due to their
fast response, and accuracy over very wide temperature ranges (Yadav, Srivastava,
Singh, Kumar, & Yadav, 2012).
Thermistors
A TM is a wired sensor made from a semi-conductive metal that exhibits an
inverse relationship between temperature and the electrical resistance within the
device. Like TC’s, TM’s need a data logger to control thermocouple sampling rates
and store recorded data. TM’s have a high thermal sensitivity, fast response rate and
very accurate when measuring temperatures within the human physiological range
(≤100 °C; Klopfenstein, 1994).
iButtons®
An IB is a relatively new wireless device that is an autonomous, encapsulated
semiconductor sensor approximately 16 x 6mm2 in size. The IB’s major advantage
over the former conductive devices is wireless recording of temperatures. The IB has
been validated against more traditional TM (Harper Smith et al., 2010) and
thermocouples (van Marken Lichtenbelt et al., 2006), and has been shown to
successfully measure long-term 𝑇sk of extremities of both diabetic and healthy
subjects in free-living conditions (Rutkove et al., 2009). However, the major
Chapter 2: Literature Review 31
drawback of the IB’s is that data must be viewed retrospectively once the device has
finished logging. Both the TM’s and the IB’s were chosen as the conductive devices
to be used as part of experimental testing during this project (details in Chapter 4,
Table 4.1 Device specifications).
2.8.2 Considerations When Using Conductive Devices
By design, conductive measurement devices must be in contact with the skin.
A wide variety of methodological factors have been shown to influence temperature
measurements in research settings. These include contact pressure, probe placement,
fixation method, sensor age and environmental conditions.
The application of adhesive tapes to 𝑇sk probes has the potential create a
microenvironment and disrupt heat transfer capacity through convection and
evaporation (Gonzalez & Sawka, 1988). Previous investigations have cited the lack
of consistency or reporting of attachment methods for conductive devices (Buono &
Ulrich, 1998; Tyler, 2011). Buono and Ulrich (1998) studied the influence of
‘covered’ and ‘uncovered’ TM measurements of 𝑇�sk during exercise in different
environmental conditions (thermoneutral, hot-humid and hot-dry). On three separate
occasions, subjects were required to walk for 30-min (6.4 km/h, 0% grade) while 𝑇�sk
was logged to the nearest 0.1 °C every 5-min with the TM’s taped to the skin and
held to the skin with an acrylic ring and elastic bands. Covered probes recorded
significantly higher temperatures under all conditions, ranging from 0.4 °C in hot-dry
to 1.3 °C in thermoneutral. Similar findings were noted by Tyler (2011) who
compared uncovered to covered TM’s of varying layers of tape in thermoneutral,
warm and hot conditions. Expectedly, temperature differences rose with additional
layers of tape which lead to a significant overestimation of 𝑇�sk between almost all
uncovered and layered methods. A more recent laboratory based study of 𝑇�sk devices
measuring a hot plate (36.5 °C) found temperature readings are significantly
influenced by the conductance of the tape, sensor shape and contact to the surface
and the ambient temperature (Psikuta, Niedermann, & Rossi, 2013).
Several layers of adhesive tapes are often applied to conductive devices to
ensure good contact and pressure, especially during exercise where movement and
sweat can lead to loss of contact (Buono et al., 2007). However, the surface contact
and pressure of the sensor itself can alter temperature measurements. Original
32 Chapter 2: Literature Review
investigations by Stoll and Hardy (1950) found doubling contact pressure of
thermocouple probes could see temperature increases of up to 1.5 °C. Moreover, any
deviation in angular contact between the probe surface and the skin could lead to
erroneous readings drifting toward ambient temperature (Harper Smith et al., 2010).
Ambient temperatures have also been shown to influence the performance of
𝑇sk devices (Psikuta et al., 2013; van Marken Lichtenbelt et al., 2006). In a human
study of measurement differences between IB’s and TC’s in cold (15.5 °C; 8.6 %
RH) and hot (34.9 °C; 64 % RH) conditions, compared to the TC’s the IB’s
constantly underestimated 𝑇�sk in the cold (-0.24 °C) and constantly overestimated
𝑇�sk in the heat (0.88 °C; van Marken Lichtenbelt et al., 2006). These findings could
be intrinsically related to the composition and shape of the probes and their response
to thermal inertia of the ambient temperature in extreme conditions. Furthermore, the
impact of temperature changes to TC wires and the not sensing probe itself, have all
been reported (Jutte, Long, & Knight, 2010). In a water bath study of a number of
TC models, increased measurement artefacts were seen in TC probes after ice bags
were placed on top of the TC leads (Jutte et al., 2010).
Because of the dynamic nature of skin and the subcutaneous properties that
alter 𝑇sk (blood flow, fatness, metabolic rate), subjective probe placement within
regions of interest can lead to unreliable temperature measurements (Frim et al.,
1990; Pascoe et al., 2012). The placements of conductive devices within a specific
region of interest are described or depicted with each formula. Often, these
recommendations do not provide accurate or repeatable instructions for the
placement of probes based upon objective anatomical landmarks, but rather a vague
representation of placement, open to interpretation. Pascoe et al. (2012) used infrared
thermography to measure 𝑇sk variation across 13 commonly used 𝑇sk sites to
quantify the possible error associated with TM placement. The average temperature
site variation was 3.19 ± 0.93 °C. When the hottest and coolest measured
temperatures of the appropriate sites were transposed into the Burton (1934) 3-site
formula, the output 𝑇�sk had a range of 29.99 to 33.51 °C (difference = 3.52 °C). In
addition, it would be expected that this observed variation across the skin surface
would be magnified in colder ambient conditions where vasoconstriction occurs
(Frim et al., 1990).
Chapter 2: Literature Review 33
2.8.3 Infrared Devices
Typically, infrared devices are used as a non-contact form of 𝑇sk measurement.
This review will focus on two types of thermographic instruments: infrared
thermometers (IT) and infrared thermal imaging cameras (IC). With the advent of
more technological advances and cheaper costs associated with infrared devices,
there has been a renewed interest in use of thermography in exercise science due to
superior data collection and non-contact nature (Costello et al., 2013).
All objects hotter than absolute zero (-273.15 °C), produce an electromagnetic wave
of radiation proportional to the electrical charge given off by vibrating atoms and
molecules that make up the object. Emissivity (ε) is the term used to describe the
amount of absolute radiation energy released from an objects surface relative to an
ideal black body (ε = 1.0; Blatteis et al., 2001). By knowing the emissivity
coefficient of an object’s surface it is possible to know the surface temperature of
that object (Modest, 2013). Human skin, irrespective of ethnicity, has an emissivity
resembling that of a perfect black body between 0.97-0.99 (Boylan, Martin, &
Gardner, 1992; Sanchez-Marin, Calixto-Carrera, & Villaseñor-Mora, 2009; Steketee,
1973; Togawa, 1989). The Stefan-Boltzmann law states that the power emitted per
unit area of the surfaces of a black body is directly proportional to the fourth power
of its absolute temperature:
P = εσAT4
where
P = power radiated (watts)
A = surface area (m2)
ε = emissivity (no units)
σ = Stefan-Boltzmann Constant (5.67x10-8 W m-2 K-4)
T= absolute temperature (Kelvin)
Figure 2.1 represents the electromagnetic spectrum which makes up
wavelengths outside of, and including, the visible light spectrum seen with the naked
human eye. Increased radiation energy is associated with shorter wavelengths and is
therefore more dangerous (e.g., gamma rays). Visible light makes up a small portion
of the electromagnetic spectrum and is between wavelengths of 380 to 780 nm.
Infrared 𝑇sk devices measure long-wave infrared radiation between wavelengths of
7500 and 14000 nm (7.5-14 µm). They detect the infrared radiation emitted from an
34 Chapter 2: Literature Review
object within this range, and covert the input into an electrical signal which is
displayed in an output temperature or image (discussed further in following
sections).
Figure 2.1. The electromagnetic spectrum, depicting various properties including visible light and long-wave infrared radiation
Infrared Thermometers
Similar to the conductive devices mentioned previously (section 2.6.1
Conductive Devices), IT’s measure the average temperature over a small area, often
referred to as a ‘spot’ measurement. There are infrared thermometers that require
contact with the area of measurement (i.e., skin). However, the majority of infrared
devices are held off the skin which allows for temperature measurements without any
physical contact. An internal detector collects the infrared energy of an object with a
relatively simple ‘point and shoot’ design with an associated laser sighting for
aiming purposes. Most clinically used devices have manufacturer specified distances,
in which the device should be held from the skin to ensure accurate measurement
(e.g., 50 mm). Some other IT’s however, use a distance to spot ratio that allows for a
greater measurement area at longer distances, but at the cost of accuracy (Thomas,
2006). ASTM international standards (ASTM-E1965, 1998) state that prior to use an
IT “shall be stabilised at given conditions of ambient temperature and humidity for a
minimum of 30-min or longer if so specified by the manufacturer”. There are now
more advanced models with manual and automatic ambient re-calibration settings for
the use of IT’s in varying environmental conditions without the need for waiting for
stabilisation (e.g., testing air conditioning then moving outside).
Chapter 2: Literature Review 35
Infrared Cameras
IC’s are characterised into two categories: cooled and uncooled. Cooled
cameras require liquid nitrogen cooling and produce more accurate and sensitive
measurements (Qi & Diakides, 2007). These cameras cost well outside the budgets
of typical research laboratories and are used almost exclusively in military
engineering and commercial industries. Uncooled cameras used predominantly in
medical settings are compact, portable and markedly cheaper than their cooled
counterparts (Diakides, 1997); but the initial and associated costs make them a
relativity expensive 𝑇sk measurement device compared to cheaper conductive and IT
options. The use of an uncooled IC typically requires the camera, a tripod and a
connected computer for image display and image processing via dedicated software.
The continual development of infrared thermography has seen it become widely
adopted as a diagnostic tool among the medical community with recent medical
applications including mass fever screening (Ring & Ammer, 2012); breast cancer
monitoring and detection (E. Ng, 2009); observation of osteoarthritic progression and
identification of overuse injury such as ‘tennis elbow’ (Hildebrandt et al., 2010).
Modern uncooled IC’s exhibit an erroneous thermal drift when turned on or
moved (Ring et al., 2007) and therefore, much like IT’s, require time to stabilise to
the surrounding ambient conditions for accurate measurement (normally 30-60 min;
Grgić & Pušnik, 2011). An uncooled IC and a clinical standard used IT were used
for all testing as part of this project (details in Chapter 4, Table 4.1 Device
specifications).
2.8.4 Considerations When Using Infrared Devices
The identification and selection of regions of interest for studies implementing
IC’s are poorly standardised, leaving authors to select their preferred measurement
area within a previous defined region of interest or create their own. For example, as
of 2009 up to 20 different angles, field of view and image analysis were reported to
measure hand temperatures (Ammer, 2009). This variation has been shown to lead to
significant 𝑇sk differences between methods of image analysis (Ludwig, Formenti,
Gargano, & Alberti, 2014), increase unreliable measurements within and between
both subjects and operators (Ring & Ammer, 2000; Zaproudina et al., 2008), as well
as confining the accurate comparison of thermography studies. A number of authors
have tried to implement their own universal region of interest standardisation with
36 Chapter 2: Literature Review
limited adoption from the greater scientific community (Ammer, 2008; Fernández-
Cuevas et al., 2012). A consensus for the universal standardisation of regions of
interest, using more objective means, such as inert markers attached to anatomical
landmarks, need to be established to help improve 𝑇sk measurements derived from
thermal images.
IC set up including measurement position, distance and environmental
conditions can influence the quality of data collected. Camera distance should vary
upon the size of the measurement area and the optical specifications of the camera.
To maximise data collection by increasing functional pixels, the IC should be placed
as close as possible so the measurement surface fills the entire field of view while
maintaining focus (Ammer, 2003). For the most accurate temperature measurements
infrared devices are required to be positioned perpendicular to the measurement
surface of interest. Any deviation away from 0° causes the device to read thermal
radiation from the surroundings being reflected from the skin (Watmough, Fowler, &
Oliver, 1970). Ammer (2003) reported deviations between 0 and 30° alter the
emissivity values of the skin and begin to limit the radiative energy measured by the
device, while deviations of 30 and 60° produce substantially erroneous data (±1 °C).
In order to minimise any environmental influences, data collection should be
conducted in a stable controlled setting of 18 to 25 °C (Ring & Ammer, 2000), free
of external radiation sources (i.e., sun) and the use of a uniform. Matte background
behind the participant is recommended to avoid any reflective radiation.
Finally, the presences of ointments, cosmetics, liquids and hair on the
measurement area can cause inaccurate 𝑇sk readings (Bernard, Staffa, Mornstein, &
Bourek, 2013; Korichi et al., 2006; Steketee, 1976). The topical application of water,
creams and gels has been shown to produce reductions in 𝑇sk measurements through
infrared means by up to 4.86 °C (Bernard et al., 2013). Further to this, human hair is
an avascular structure with a lower emissivity, thermal conductivity and heat
capacity than human skin and has been shown to produce relativity lower
temperatures than hair-free skin (Togawa & Saito, 1994). Few authors have
controlled for hair along the skin during infrared imaging, advising that any relevant
body hair is removed in the days preceding testing to avoid micro-trauma from
shaving and consequently artificially raising 𝑇sk (Merla et al., 2010). Overall, each of
these substances mentioned creates a physical barrier, with unique emissive and
Chapter 2: Literature Review 37
thermal properties, between the skin surface and the infrared detector. Therefore, it
should be recommended that before infrared 𝑇sk measurements, participants should
have any relevant regions of interest cleaned with alcohol (allowed to dry) and be
free of hair.
2.9 DEFINING INTERCHANGEABLILTY
A correlation coefficient is a measure of the strength of linear dependence
between two variables and does not measure the strength of the agreement. For
example, comparing 𝑇sk values derived from a TM and IC would achieve a perfect
correlation if all recorded data points fell along any straight line (Bland & Altman,
1995). However, a perfect agreement between the two methods would require the
data to fall along the same line as one another. In order to ensure that two separate
measurements techniques are classified as interchangeable (i.e. in agreement), more
robust techniques such as the comparison of mean differences are needed (Bland &
Altman, 1986). Current practice suggests that for any two conductive and infrared
𝑇sk devices to be considered interchangeable, mean temperature differences should
not exceed the proposed clinical significant difference of 0.5 °C (Joly & Weil, 1969;
Kelechi et al., 2011; Kelechi et al., 2006; Selfe et al., 2008). Statistical significant
differences between means will also be determined throughout the subsequent
original investigations. Therefore for the purpose of this thesis, devices will only be
considered interchangeable if they do not exceed clinical (mean differences >0.5 °C)
and statistical (P < 0.05) significance.
2.10 CONCLUSION
This literature review aimed to explain the mechanisms by which the human
body thermoregulates and more specifically how the skin facilitates heat loss or gain.
Furthermore, it was explained how 𝑇sk is influenced by a variety of intrinsic and
extrinsic factors and the limitations of each of the devices typically used to measure
the temperature of human skin. The following section (Chapter 3) narrows the focus,
by systematically reviewing the current literature that has compared infrared and
conductive devices to determine if there is a consistent bias between the two
modalities.
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review 39
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
3.1 INTRODUCTION
Skin temperature (𝑇sk) is an important physiological measure that can reflect
the presence of illness and injury as well provide insight into the localised
interactions between the body and the environment. 𝑇sk has a wide range of
applications that consist of, but are not limited to, the assessment of; overuse injuries
(Hildebrandt et al., 2010; Meknas, Odden-Miland, Mercer, Castillejo, & Johansen,
2008), physiological strain (Cuddy et al., 2013), hypoxia (Cipriano & Goldman,
1975), exercise performance,(Davis & Bishop, 2013; Kenefick, Cheuvront, Palombo,
Ely, & Sawka, 2010; Levels, de Koning, Foster, & Daanen, 2012; Price, 2006; Ross,
Abbiss, Laursen, Martin, & Burke, 2013; Schlader, Simmons, Stannard, & Mundel,
2011; Wegmann et al., 2012), pacing strategies (Tucker, 2009), cold exposure
(Bleakley et al., 2012; Costello, Algar, & Donnelly, 2012; Kennet, Hardaker, Hobbs,
& Selfe, 2007; Selfe, Hardaker, Thewlis, & Karki, 2006), fever screening (Bitar et
al., 2009; Chan et al., 2004; Chiu et al., 2005; Nguyen et al., 2010), thermal comfort
and sensation (Wang et al., 2007), circadian rhythm (Hasselberg et al., 2013; van
Marken Lichtenbelt et al., 2006; Yosipovitch et al., 1998), complex region pain
syndrome (Koban, Leis, Schultze-Mosgau, & Birklein, 2003; Wasner et al., 2002)
and when coupled with core body temperature can determine mean body temperature
(Colin et al., 1971). Consequently, the assessment of 𝑇sk is extremely important in
sports medicine, exercise science, occupational, clinical and public health settings.
Thermoreceptors located within the hypothalamus, spinal cord, skin and some
abdominal organs monitor temperature changes, and work via negative feedback to
initiate autonomic mechanisms to either conserve (via shivering and
vasoconstriction) or lose (via sweating and vasodilation) body heat (Casa et al.,
2007). The human body controls core body temperature within a tight band typically
between 36 and 38 °C despite varying ambient temperatures. When core temperature
rises, for example during exercise, the anterior hypothalamus detects the temperature
40 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
of blood perfusing it and once temperatures exceed an internal set point, vasodilation
of peripheral blood vessels and evaporation of sweat generated along the skin surface
facilitates heat loss (Charkoudian, 2003). As a result, 𝑇sk is influenced by a number
of factors including superficial blood flow, heat conduction from deeper tissues
(including muscle) and heat loss along the skin surface (Sawka, Leon, Montain, &
Sonna, 2011). The skin is also the site of reciprocal heat transfer between the human
body and the external environment. The extent to which heat transfer occurs is
largely dependent on the environmental conditions, such as ambient temperature,
water vapour and the thermal properties of human skin (Prek & Butala, 2010). For
example, radiation energy, the loss or gain of heat from infrared rays, imposed upon
the skin through the surrounding environment, increases thermal loads as a function
of the skin absorption characteristics and emissive properties (Cohen, 1977).
The most common methods of assessing 𝑇sk are derived from conductive and
infrared devices (Table 3.1). These techniques measure temperature by applying
different scientific principles of thermal heat transfer. Conductive methods are based
upon thermal conduction as a result of physical contact between the object of interest
and the measurement device (Boetcher, Sparrowb, & Dugay, 2009). To assess 𝑇sk,
this contact is typically made by affixing the device to the skin via medical adhesive
tape. Infrared devices detect thermal radiation in the infrared spectrum that is emitted
from the skin (Anbar, 2002). While most infrared devices are non-contact (e.g.
thermal imaging), it is necessary for some handheld infrared thermometers to be
placed against the skin. Popular conductive devices include thermistors (TM),
thermocouples (TC) and iButtons®; while popular infrared devices include thermal
imaging cameras (IC) and handheld infrared thermometers (IT). All devices vary in
cost (Foto, Brasseaux, & Birke, 2007; Harper Smith et al., 2010), error (Bernard et
al., 2013; Boetcher et al., 2009; Harper Smith et al., 2010; Psikuta et al., 2013),
response time (Foto et al., 2007; Harper Smith et al., 2010; van Marken Lichtenbelt
et al., 2006) and reliability (Hasselberg et al., 2013; Long, Jutte, & Knight, 2010;
Versey, Gore, Halson, Plowman, & Dawson, 2011; Zaproudina et al., 2008).
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review 41
Table 3.1.
Description of devices
Device Description C
ondu
ctiv
e D
evic
es
Thermocouple
A surface temperature probe based upon the Seebeck effect, where by temperature
measured is proportional to the voltage between two dissimilar metals in the presence of a
temperature gradient.
Thermistor A surface temperature probe with an internal temperature sensitive resistor that measures
temperature by using a non-linear relationship between resistance and temperature; i.e., as
the temperature of a thermistor increases, the resistance within the thermistor decreases.
Both Thermistors and Thermocouples are typically connected to an associated data
logger.
iButton® A small (~16 x 6mm2), self-enclosed, self-sufficient, programmable, wireless device that
stores temperature values in an internal memory for retrospective extraction.
Infr
ared
Dev
ices
Thermal
Imaging
Camera
Within a video camera a radiometer detects infrared energy as a function of temperature
and converts the electronic video signal into an image displayed on a connected computer.
Temperatures are represented in grayscale or various colours with a single pixel
representing one temperature datapoint. Users have the ability to select specific regions of
interest from the image with post-analysis software.
Handheld
Infrared
Thermometer
Typically a stand-alone device that gives a single temperature reading by assessing
infrared energy at a localised ‘spot’ measurement. The device optics and the distance from
the object of interest determine the size of the spot measurement. However, some
thermometers are designed to be in contact with the object of interest. Tympanic infrared
thermometers are also used clinically to assess 𝑇sk.
Extensive investigations regarding the validity of the method of core
temperature measurement have taken place, with rectal thermometers widely
regarded as the gold standard of core body temperature measurement (Binkley et al.,
2002; Casa et al., 2007; Ganio, Brown, Casa, Becker, & Yeargin, 2009; Moran,
2002). Conversely, 𝑇sk has no recognised criterion (Harper Smith et al., 2010).
Despite the obvious differences in measurement techniques, and indeed the heat
transfer principles of the devices used to assess 𝑇sk, few authors have considered the
potential difference between conductive and infrared technologies. Furthermore, over
the past decade considerable advances in the technology leading to greater accuracy,
functionality and affordability have seen infrared devices, particularly thermal
imaging, become more widely adopted (Costello, McInerney, et al., 2012; Costello et
al., 2013). However, a brevity of research exists within the literature comparing
42 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
measurement differences between conductive and infrared techniques (Costello,
McInerney, et al., 2012).
Despite the differences in scientific principles underpinning each method,
many scientists and clinicians assume interchangeability between devices under all
circumstances. Current practice suggests that for any other device to be considered
interchangeable temperature differences should not exceed the proposed clinical
significant difference of 0.5 °C (Joly & Weil, 1969; Kelechi et al., 2011; Kelechi et
al., 2006; Selfe et al., 2008). Importantly, these relatively low thresholds illustrate
that only small variations between devices are needed to produce erroneous data that
significantly influences the conclusions drawn by researchers and clinicians. Due to
the significant role of 𝑇sk in thermoregulation and pathophysiology, a systematic
review examining the validity of using conductive and infrared devices
interchangeably is required. Therefore, our aim was to review the irregularities
between conductive and infrared means of assessing 𝑇sk which are commonly
employed in exercise science and sports medicine.
3.2 METHOD
3.2.1 Search Strategy
Searches were performed in the Cochrane Central Register of Controlled
Trials, MEDLINE, SportsDiscus and CINHAL. A total of 19 MeSH or keywords and
their combinations were searched using Boolean operators (skin temperature, tissue
temperature, surface temperature, valid*, reliab*, repeatability, interchange*,
compar*, contrast, differences, contact, non-contact, ibutton*, thermograph*,
thermistors, thermocouples, thermometer, infrared camera, thermal imag*). Each
database was searched from January 1998 to February 2014. Potentially relevant
articles were also obtained by physically searching the bibliographies of included
studies to identify any study that may have escaped the original search. A total of
6036 articles were identified (Figure 3.1).
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable?A Systematic Review 43
Figure 3.1. PRISMA flow chart describing the selection and exclusion of articles.
3.2.2 Inclusion Criteria
Due to the advent of digital technology and substantial technological advances
in the last 15 years, original papers published since 1998 were preferentially
considered. In addition, studies meeting the following criteria were included in the
review: 1) the literature was written in English, 2) participants were human (in vivo),
3) skin surface temperature was assessed at the same site, 4) with at least two
commercially available devices employed – one conductive and one infrared – and 5)
had 𝑇sk data reported in the study.
3.2.3 Data Extraction and Management
Data were extracted independently by two review authors using a customised
form. This was used to extract relevant data on methodological design, participants,
comparisons of devices (conductive and infrared) and techniques used, region of
interest and environmental conditions. Any disagreement was resolved by consensus,
44 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
or third-party adjudication. Although measurement devices may have been reported
significantly different (statistically); if a study reported mean differences within 0.5
°C, for the purpose of this review they were classified as interchangeable. Where
numerical values were not reported, data was manually extracted from any relevant
graphs or figures. There was no blinding to study author, institution or journal at this
stage.
45 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
Table 3.2. Details of articles included in the systematic review
Authors Techniques Sample Size (M:F);
Age (y)^ Sites Methods and Conditions Findings
Conductive Infrared
Buono et al. (2007)
(observational)
TMA ITB 6 (0:6) healthy;
25 ± 3
𝑇�sk reported – 3 site formula[52]
(Chest, Forearm
and Calf)
1. Seated rest
Acclimatisation = 10-min
Troom = 15, 25 & 35 °C
(40 % RH)
Other = wind speed (ν <1.0 m·s-1) 2. Treadmill
(4.82 km·h-1, 0% Grade)
Duration = 15-min
Troom = 15, 25 & 35 °C
(40 % RH)
1. Rest#
15°C: IT < TM (0.2 °C)
25°C: IT > TM (0.4 °C)
35°C: IT > TM (0.9 °C)
2. Exercise#
15°C: IT < TM (0. 1°C)
25°C: IT < TM (0.6 °C)
35°C: IT > TM (0.1 °C)
Burnham et al. (2006) (observational)
TMC 1. ITD
2. ITE
17 (12:5) healthy;
29.5 ± 8.5
Shoulder
Forearm
Hand
Thigh
Shin
Foot
Mode = NR
Acclimatisation = NR
Troom = NR
1. ITD vs. TM
Shoulder: IT < TM (0.7 °C)
Forearm: IT < TM (0.5 °C)
Hand: IT < TM (0.5 °C)
Thigh: IT < TM (0.5 °C)
Shin: IT < TM (0.3 °C)
Foot: IT < TM (0.4 °C)
All Sites: IT < TM (0.5 °C)
2. ITE vs. TM
Shoulder: IT < TM (0.2 °C)
Forearm: IT < TM (0.1 °C)
Hand: IT < TM (0.2 °C)
Thigh: IT < TM (0.3 °C)
Shin: IT < TM (0.1 °C)
Foot: IT < TM (0.2 °C)
All Sites: IT < TM (0.2 °C)
Fernandes et al. (2014) (randomised crossover)
TCF ICG 12 (12:0) healthy;
22.4 ± 3.3 𝑇�sk reported –
8 site formula[55]
(Forehead, Chest,
Abdomen, Scapula,
Arm, Forearm,
Thigh and Calf)
1. Standing rest
Acclimatisation = 60-min
2. Treadmill (60 %VO2max)
Duration = 60-min
3. Standing recovery
Duration = 60-min
Troom TC = 24.9 ± 0.6 °C
(62.3 ± 5.7 % RH)
Troom IC = 24.8 ± 0.4 °C
(61.9 ± 5.4 % RH)
1. Rest
IC > TC (0.75 °C)
2. Exercise
IC < TC (1.22 °C)
3. Recovery
IC > TC (1.16 °C)
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review 46
Study (Type)
Techniques Sample Size (M:F); Age (y)#
Sites Methods Findings Conductive Infrared
Kelechi et al. (2011) (observational)
TMH ITI 17 (12:5) healthy;
29.5 ± 8.5
Medial Aspect of
Right Lower Leg
Lying rest
Acclimatisation = 10-min
Troom = 23 ± 1.3 °C (% RH = NR)
Other =
1. post 10-min acclimatisation
2. further 10-min
3. after 10-min cold application
1. IT > TM (0.2 °C)*
2. IT > TM (0.1 °C)*
3. IT > TM (0.3 °C)*
Kelechi et al. (2006) (observational)
TMJ ITK 55 (26:29);
69.8 ±11.5
Medial Aspect of Lower Legs
Seated rest
Acclimatisation = ~30-min
Troom = 22 °C (% RH = NR)
Other = Assessed on 3 days (7 days apart)
1. Left Leg: IT < TM (0.13 °C)
2. Left Leg: IT < TM (0.16 °C)
3. Left Leg: IT = TM (0.00 °C)
Right Leg: IT < TM (0.10 °C)
Right Leg: IT < TM (0.09 °C)
Right Leg: IT < TM (0.21 °C)
Korukçu and Kilic (2009) (observational)
TCL ICM 3 (3:0) healthy;
25 ± 2.6
Face
Forearm
Finger
1. Passive heating
2. Passive cooling
Duration = 30-min (each)
Troom = NR
1. IC < TC (°C = NR)
2. IC > TC during cooling (°C = NR)
Maximum differences between IC and TC <2°C at any instance during heating or cooling period.
Matsukawa et al. (2000) (observational)
TCN ITO 10 (10:0) healthy;
30 ± 5
Forearm
Finger
Recovery from localised passive heating
Duration = 30-min
Troom = 22 – 23 °C (% RH = NR)
Forearm: IT < TC (0.5 °C)
Finger: IT < TC (0.5 °C)
Roy et al. (2006) (observational)
TMP ITQ 17 (6:11) healthy;
25.6 ± 5.4
Paraspinal
(C4 & L4)
Prone rest
Acclimatisation = 20 – 30-min
Troom = 20.5 - 23.3 °C (% RH = NR)
Other = Repeated on 4 other days
Overall:
Left C4: IT > TM (1.23 °C)
Left L4: IT > TM (1.56 °C)
Right C4: IT > TM (1.67 °C)
Right L4: IT > TM (1.62 °C)
Ruopsa et al. (2009)
(observational)
TCR ITS 38 (NR); NR Middle finger of
both hands
Mode = NR
Acclimatisation = NR
Troom = NR
At 𝑇sk between 31.5 – 35 °C:
IT < TC (0.06 °C)
At 𝑇sk between 21.5 - 31.4 °C:
IT < TC (1.01 °C)
47 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
Authors Techniques Sample Size (M:F);
Age (y)# Sites Methods and Conditions Findings
Conductive Infrared
van den Heuvel et al (2003)
(observational)
TMT ICU 4 (1:3) healthy;
26.8 ± 2.2
Fingertips
Palms
Forearms
Feet
Seated or supine rest
Acclimatisation = 15-min
Troom = 25 ± 1 oC (% RH = NR)
On average across all sites, IC < TM (2.32 °C)
TM = Thermistors, TC = Thermocouples, IT = Handheld Infrared Thermometer, IC = Infrared Camera, M = Male, F = Female, 𝑻𝐬𝐤 = Skin Temperature, 𝑻�𝐬𝐤 = Mean Skin Temperature, Troom = Room Temperature, RH =
Relative Humidity, NR = Not Reported. ^ = Data for ages are presented in years (means ± SD) or not reported where stated. * = Received through first author correspondence. # = Derived from graphs presented in
publication.
A = Series 400 (YSI, Ohio, USA), B = (Extech Instruments, Massachusetts, USA); C = 113050 (Rochester Inc., New York, USA), D = 3000A (Genius, Sherwood IMS, California, USA), E = DT-1001 (Exergen,
Massachusetts, USA); F = S-09K thermocouples (Instrutherm, São Paulo, Brazil), G = ThermaCam T420 (FLIR Systems, Oregon, USA); H = PeriFlux 5020 Temperature Unit (Perimed, Stockholm, Sweden), I =
TempTouch (Diabetica Solutions, Texas, USA); J = PeriFlux 5020 Temperature Unit (Perimed, Stockholm, Sweden), K = ThermoTrace Model 15012 (DeltaTrak, California, USA); L = T-type thermocouples
(Physitetemp, New Jersey, USA), M = ThermaCam SC640 (FLIR Systems, Oregon, USA); N = TC (Mon-a-Therm, Mallinckrodt Anaesthesiology Products, St. Louis, Missouri, USA), O = Tympanic IT with attached 𝑇sk
probe (Genius, Sherwood IMS, California, USA); P = Model Et-016-STP/OWL-ET-016-STP (General Electric via Digi-Key, Minnesota, USA), Q = Subluxation Station Insight 7000 (EMG Consultant Inc., New Jersey,
USA); R = (Datex-Engstom, Helsinki, Finaland), S = PhotoTemp MX6 (Raytek, Califonia, USA); T = Steri-Probe type 499B (Cincinnati Sub Zero, Ohio, USA), U = MMS Med2000 camera (Meditherm, Queensland,
Australia).
48 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
3.3 RESULTS
3.3.1 Included studies
Ten articles met the inclusion criteria for this review, the characteristics of
which are summarised in Table 3.2 (Buono et al., 2007; Burnham et al., 2006;
Fernandes et al., 2014; Kelechi et al., 2011; Kelechi et al., 2006; Korukçu & Kilic,
2009; Matsukawa et al., 2000; Roy et al., 2006b; Ruopsa et al., 2009; van den Heuvel
et al., 2003). One article was excluded from the current review as the data was
previously reported in another publication (Roy, Boucher, & Comtois, 2006a). This
was confirmed following personal communication with the authors. Of the ten
studies the total sample comprised of 179 participants (82 male, 59 female); the sex
of 38 participants was unknown (Ruopsa et al., 2009). The mean sample of the
pooled studies was 18, with the largest study including a total of 55 participants
(Kelechi et al., 2006). Participant mean ages ranged from 22 (Fernandes et al., 2014)
to 70 years (Kelechi et al., 2006); one study failed to report the age of the
participants (Ruopsa et al., 2009). Nine of the ten investigations used an
observational study design (Buono et al., 2007; Burnham et al., 2006; Kelechi et al.,
2011; Kelechi et al., 2006; Korukçu & Kilic, 2009; Matsukawa et al., 2000; Roy et
al., 2006b; Ruopsa et al., 2009; van den Heuvel et al., 2003), with one randomised
crossover trial (Fernandes et al., 2014). In relation to statistical power, only one study
(Kelechi et al., 2006) incorporated a prospective power analysis to identify the
sample size necessary to achieve statistical significance.
3.3.2 Detail of Comparisons
Of the ten included studies comparing conductive and infrared methods of
assessing 𝑇sk, four types of devices were used; thermistors (Buono et al., 2007;
Burnham et al., 2006; Kelechi et al., 2011; Kelechi et al., 2006; Roy et al., 2006b;
van den Heuvel et al., 2003), thermocouples (Fernandes et al., 2014; Korukçu &
Kilic, 2009; Matsukawa et al., 2000; Ruopsa et al., 2009), infrared cameras
(Fernandes et al., 2014; Korukçu & Kilic, 2009; van den Heuvel et al., 2003) and
handheld infrared thermometers (Buono et al., 2007; Burnham et al., 2006; Kelechi
et al., 2011; Kelechi et al., 2006; Matsukawa et al., 2000; Roy et al., 2006b; Ruopsa
et al., 2009). Within the handheld infrared thermometers, both contact (Burnham et
al., 2006; Kelechi et al., 2011; Roy et al., 2006b) and non-contact (Buono et al.,
2007; Kelechi et al., 2006; Matsukawa et al., 2000) models were utilised. In addition,
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review 49
two studies (Burnham et al., 2006; Matsukawa et al., 2000) used a tympanic infrared
thermometer to measure 𝑇sk and a single study (Burnham et al., 2006) tested three
devices, by comparing two different handheld infrared thermometers to a conductive
device. Information pertaining to the individual device model and manufacturer is
reported in Table 3.1.
Local 𝑇sk was measured at the face (Korukçu & Kilic, 2009), shoulder
(Burnham et al., 2006), paraspinal regions (Roy et al., 2006b), forearm (Burnham et
al., 2006; Matsukawa et al., 2000; van den Heuvel et al., 2003), hand and fingers
(Burnham et al., 2006; Matsukawa et al., 2000; Ruopsa et al., 2009; van den Heuvel
et al., 2003), thigh (Burnham et al., 2006), lower leg (Burnham et al., 2006; Kelechi
et al., 2011; Kelechi et al., 2006) and foot (Burnham et al., 2006; van den Heuvel et
al., 2003). Two studies (Buono et al., 2007; Fernandes et al., 2014) compared mean
skin temperature (𝑇�sk) values between devices using the 3-site (chest, forearm and
calf) equation developed by Burton (1934); and the 8-site (forehead, chest, abdomen,
scapula, arm, forearm, thigh and calf) developed by Nadel et al. (1973).
Measurements were taken with devices during rest (Buono et al., 2007;
Fernandes et al., 2014; Kelechi et al., 2011; Kelechi et al., 2006; Roy et al., 2006b;
van den Heuvel et al., 2003), exercise (Buono et al., 2007; Fernandes et al., 2014),
passive heating (Korukçu & Kilic, 2009; Matsukawa et al., 2000) and passive
cooling (Kelechi et al., 2011; Korukçu & Kilic, 2009). It was not clear what
environmental conditions were employed in two studies (Burnham et al., 2006;
Ruopsa et al., 2009). Reported ambient temperatures ranged from 15 to 35 °C
(Buono et al., 2007), with three studies failing to describe ambient conditions in
which testing took place (Burnham et al., 2006; Korukçu & Kilic, 2009; Ruopsa et
al., 2009) and only two studies reported an average relative humidity (ranging from
40 to 62%; Buono et al., 2007; Fernandes et al., 2014).
3.3.3 Risk of bias
In order to assess the strength of the current body of evidence a systematic
evaluation of the risk of bias was undertaken as part of this review. This was
conducted under four applicable measurements, random sequence generation,
allocation concealment, blinding and incomplete outcome data (Figure 3.2).
50 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
Figure 3.2. Included Studies: risk of bias summary.
3.3.4 Study heterogeneity
Meta-analyses were not undertaken because of clinical heterogeneity. This
related to clinical diversity in terms of a number of key study characteristics:
participants, environmental conditions, exercise intervention, devices and location of
𝑇sk assessment.
3.3.5 Cold Environment and Cryotherapy
Three studies (Buono et al., 2007; Kelechi et al., 2006; Korukçu & Kilic, 2009)
compared devices under cold environmental conditions. More specifically, 10 °C
ambient temperatures (Buono et al., 2007), passive air cooling (Korukçu & Kilic,
2009) and following 10-min of ice pack application (Kelechi et al., 2011). Buono et
al. (2007) found no statistical or clinical differences between a TM and an IT when
determining 𝑇�sk during passive rest or exercise in cold ambient conditions, with
mean differences (MD) of 0.2 °C (95% CI -2.63 to 3.03 °C) and 0.1 °C (95% CI -
2.97 to 3.17 °C) respectively.
Using a glycerine-based gel wrap to cool the measurement site, Kelechi et al.
(2006) reported 12/17 (71%) of measurements taken between a TM and IT were
outside the clinically important limits (>0.5 °C) with a MD of 0.3 °C. However, this
study (Kelechi et al., 2006) did not control the application of the cold gel which was
placed directly over the TM probe at different pressures and locations over the
measurement site. Consequently, these findings should be treated with caution.
Korukçu and Kilic (2009) used a TC to validate the use of an IC during passive
cooling in an automobile, recording every 10-seconds for 30-min. On average the TC
recorded greater 𝑇sk values than that of the IC, but unfortunately the mean
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable?A Systematic Review 51
differences between the devices were not reported. However, it was noted that
differences did not exceed 2 °C at any time.
3.3.6 Thermoneutral Environment
Six studies (Buono et al., 2007; Fernandes et al., 2014; Kelechi et al., 2011;
Kelechi et al., 2006; Roy et al., 2006b; van den Heuvel et al., 2003) reported that
testing was conducted in a thermoneutral environment. Two other studies (Burnham
et al., 2006; Ruopsa et al., 2009) failed to report the ambient conditions or the
positioning of the participants (i.e., seated rest, prone) but it is assumed that these
studies took place in stable thermoneutral environments with the participants
passively resting. The mean differences between conductive and infrared devices for
all thermoneutral studies are presented in Figure 3.3. Across the eight thermoneutral
studies, three found conductive instruments measured elevated 𝑇sk values compared
with their infrared counterparts; MD 0.5 °C (95% CI -0.51 to 1.58 °C; Burnham et
al., 2006), MD 1.01 °C (95% CI 0.62 to 1.40 °C; Ruopsa et al., 2009), MD 2.32 °C
(95% CI 3.39 to 1.25 °C; van den Heuvel et al., 2003). The remaining five studies
(Buono et al., 2007; Fernandes et al., 2014; Kelechi et al., 2011; Kelechi et al., 2006;
Roy et al., 2006b), reported lower conductive device temperatures: MD of 1.24 to
1.61 °C depending on site (Roy et al., 2006b); similar device temperatures: MD 0.1
to 0.2 °C (Kelechi et al., 2011) and 0.08 to 0.21 °C (Kelechi et al., 2006) depending
on time; and mixed results depending on condition, i.e., rest: MD 0.4 °C (95% CI -
3.06 to 2.26 °C; Buono et al., 2007), MD 0.75 °C (-0.03 to 1.52 °C; Fernandes et
al., 2014); exercise: MD -0.6 °C (95% CI 0.88 to -2.08 °C; Buono et al., 2007), MD
-1.22 °C (-2.61 to 0.16 °C; Fernandes et al., 2014); recovery: MD 1.16 °C (-0.15 to
2.48 °C; Fernandes et al., 2014)(All conditions depicted in Figure 3.3).
3.3.7 Hot Environment
Matsukawa et al. (2000) observed MD of 0.5 °C (95% C1 -0.12 to 1.12 °C) in
the forearm and fingers, measured by a TC and a tympanic IT attached with a
commercially available 𝑇sk probe following 30-min of passive warming. When
comparing an IT and a TM during rest and exercise Buono et al. (2007) found MDs
in 𝑇�sk of 0.9 °C (95% CI -2.12 to 0.32 °C) and 0.1 °C (95% CI -0.61, 0.41 °C)
respectively. Analogous to the passive cooling protocol, Korukçu and Kilic (2009)
stated differences for any one measurement point did not exceed 2 °C during passive
heating. However, as stated previously insufficient data was published in order to
52 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
report mean differences/effect sizes between the devices and therefore this study was
excluded from Figure 3.3.
Figure 3.3. Forest plot, skin temperature comparison for 8 of the 9 included studies: Conductive vs. Infrared, outcome: mean skin temperature difference. # Based upon
values derived from publication; * data received from correspondence with first author; C4 = Cervical vertebrae 4; L4 = Lumbar vertebrae 4; T1 = Time 1; ITD =
3000A (Genius, Sherwood IMS, California, USA); ITE = DT-1001 (Exergen, Massachusetts, USA).
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review 53
3.4 DISCUSSION
3.4.1 Evaluation of Methodological Quality
There were large limitations within the current evidence base. Sample size was
consistently small and the subsequent power of individual trials was questionable.
The number of participants in each of the included studies was generally small, with
over 75% of the included studies using a sample smaller than 18 participants. The
majority of studies failed to report a priori power analysis, potentially preventing
robust conclusions to be drawn from the evidence. There was also a consistently high
risk of bias across the studies, in terms of random sequence generation, allocation
concealment, blinding and incomplete outcome data (Figure 3.2). We acknowledge
the practical difficulties of blinding assessors and participants from localised
measurement devices. However, greater effort should be made in regards to the
randomisation of measurement devices and sites.
3.4.2 Summary of Findings
This systematic review sought to identify any measurement discrepancies
between conductive and infrared 𝑇sk measurement. Any clinically significant
differences between devices would inform exercise scientists and sports medicine
clinicians regarding the use, or validation, of these devices in clinical or research
settings. Overall, five studies found clinically significant differences (>0.5 °C)
between 𝑇sk measurements (Buono et al., 2007; Roy et al., 2006b; Ruopsa et al.,
2009; van den Heuvel et al., 2003), four studies reported overall differences between
0.1 to 0.5 °C (Burnham et al., 2006; Fernandes et al., 2014; Kelechi et al., 2011;
Kelechi et al., 2006; Matsukawa et al., 2000) and the remaining study did not report
mean differences between devices (Korukçu & Kilic, 2009).
Based on the included studies there appears to be no trend for conductive or
infrared devices to systematically overestimate or underestimate 𝑇sk. In some cases
conductive devices tended to measure higher 𝑇sk than infrared (Burnham et al., 2006;
Fernandes et al., 2014; Matsukawa et al., 2000; Ruopsa et al., 2009; van den Heuvel
et al., 2003), in other cases infrared instruments tended to measure higher than
conductive (Buono et al., 2007; Fernandes et al., 2014; Kelechi et al., 2011; Kelechi
et al., 2006; Roy et al., 2006b). It is plausible that the heterogeneity in the
methodological designs of the included studies led to the contrasting findings in the
54 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
current review; more specifically, the absence of standardisation for skin temperature
sites, device employment and environmental conditions.
In the studies where conductive overestimation of 𝑇sk was observed, it would
most likely be attributed to the microenvironment created by fixation to the skin,
increasing the 𝑇sk directly below the measurement probe (Buono & Ulrich, 1998;
Psikuta et al., 2013; Tyler, 2011). This insulation of the measurement area blunts the
skin capacity to remove heat directly below the contact probe, artificially raising the
𝑇sk readings. The extent to which tape influences temperature measurements varies
on the amount applied (Tyler, 2011) and the type of tape used (Psikuta et al., 2013)
(e.g. adhesive woven fabric vs. permeable non-woven tape). The tendency for
infrared devices to measure lower 𝑇sk is supported by a recent review of temperature
measurements at several sites around the knee in over 2900 participants (Ammer,
2012). The included studies in the review by Ammer (2012) utilised a single
measurement technique and when pooled with comparable studies, it was noted on
average that regardless of health status, contact thermometers measured hotter knee
temperatures than that of infrared thermography (1 °C in healthy and up to 2 °C in
unhealthy).
Interestingly, in the three studies (Buono et al., 2007; Fernandes et al., 2014;
Kelechi et al., 2011) that recorded measurements at rest in a thermoneutral
environment, as well as applying an external stressor (i.e., exercise, localised cold
application), mean differences were augmented between devices after the
introduction of the additional variable. The influence to which an intervention (i.e.
exercise, ambient or localised temperature changes) exacerbates differences between
devices is largely unknown, with small sample sizes and limited literature comparing
instruments under these acute settings.
Fernandes et al. (2014) used a randomised crossover design to compare
thermocouples and an infrared camera on separate days. The ability to make accurate
comparisons between the two devices was dependent on the homogeneity of baseline
𝑇sk of the same person between the two testing days. The authors attempted to
control for the natural 24-hour circadian variation in 𝑇sk, by conducting testing at the
same time of day. However, day-to-day variations in skin blood flow (Sundberg,
1984) and 𝑇sk (Sarabia et al., 2008) have previously been reported in healthy subjects
even when time of day is controlled for. Therefore, it is possible that differences may
Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review 55
have been affected by the methodological design of the study. Nevertheless, there
seems to be a confounding factor that influences measurement differences between
conductive and infrared devices as a result of the commencement (Buono et al.,
2007; Fernandes et al., 2014) and cessation (Fernandes et al., 2014) of exercise.
3.4.3 Limitations and Future Research
The current review involved an exhaustive search based on a comprehensive
list of electronic databases and extensive supplementary searching; however, there
were some limitations. Studies included in this review were restricted to English; and
relevant articles may have been overlooked in the grey literature. Additionally, one
study (Buono et al., 2007) had data manually extracted from graphs and figures.
Although this was undertaken by independently by two reviewers, with
inconsistencies checked through reviewer consensus and a third party, it still serves
as an estimation of the mean difference.
The cooler end of the human physiological 𝑇sk range (<5 °C) is associated with
localised 𝑇sk damage (e.g., frost bite). The upper end (43 °C) represents the
maximum allowable localised 𝑇sk during occupational activities (International
Organisation for Standardisation, 2004b). The brevity of research comparing device
measurement accuracy along the limits of the 𝑇sk continuum is therefore concerning.
This should be a priority of researchers as these severe environmental and physical
conditions are where accuracy is critical for minimising potential injury (i.e., frost
bite, heat stress). Therefore, future research should compare and contrast differences
between an assortment of commonly used conductive and infrared devices through
the human 𝑇sk range, during rest, exercise and recovery, under different ambient
conditions (including cold exposure) to better understand the inaccuracies and
sources of error between conductive and infrared devices. Further to this, research
examining if differences between devices are exacerbated between sexes, health
status, population (young vs. elderly; lean vs. obese) and/or ethnicity is warranted.
3.5 CONCLUSIONS
The current evidence suggests that conductive and infrared devices are not
interchangeable or within the current clinical recommendations in resting conditions.
However, there is no trend for conductive or infrared devices to consistently
overestimate 𝑇sk in comparison to each other. Due to limited and ambiguous
56 Chapter 3: Are conductive and infrared devices for measuring skin temperature interchangeable? A Systematic Review
findings, it is unclear if these techniques of assessing 𝑇sk provide similar values in
the presence of external (e.g., exercise) or environmental (e.g., cold/heat exposure)
stimuli. Until more conclusive evidence is available, exercise scientists and sports
medicine practitioners need to be cognisant that conductive and infrared devices may
not be interchangeable.
Chapter 4: Correction formula of infrared and conductive thermometry 59
Chapter 4: Correction formula of infrared and conductive thermometry
4.1 INTRODUCTION
It may be assumed that conductive and infrared devices are interchangeable
even in the absence of a gold standard skin temperature (𝑇sk) measurement and the
wide variety of measurement devices available on the market. Provided one device
has been validated against a reference standard or certified thermometer, for any
other device to be considered interchangeable, temperature differences should not
exceed the proposed clinical significant difference of 0.5 °C (Kelechi et al., 2011).
This relativity small temperature difference represents the maximum allowable
disagreement between 𝑇sk measurement devices and any deviation outside of these
limits could influence the interpretation of results, diagnosis and therefore treatment
outcomes. For example, it has been shown that asymmetries in 𝑇sk >0.5 °C in post-
operative knee joints represents abnormalities which potentially affect therapeutic
management (Mayr, 1995) and that the same asymmetrical differences were first
successfully used as a diagnostic tool for tibial stress fractures (Goodman et al.,
1985).
Despite a documented failing for manufacturers of 𝑇sk devices to meet
accuracy claims (Foto et al., 2007; Jutte, Knight, & Long, 2008; Jutte et al., 2005;
Long et al., 2010; Versey et al., 2011), it is common for studies measuring 𝑇sk not to
calibrate the instruments against a known criterion before use. For instance, a brief
review of the literature reveals that 71 papers published between 2001 and 2013 in
the Journal of Applied Physiology reported human 𝑇sk as a primary outcome
variable. Of these only four studies (<6%; Brajkovic & Ducharme, 2003; Brajkovic,
Ducharme, & Frim, 2001; Jay et al., 2007; Peter, 2003) reported that any form of
calibration was conducted on 𝑇sk devices before human data collection. Typically,
water bath calibration is used as the gold standard for research laboratories to test the
validity, reliability and to quantify linear regression coefficients of conductive 𝑇sk
devices such as thermistors, iButtons® and thermocouples (Harper Smith et al., 2010;
van Marken Lichtenbelt et al., 2006); as well as core temperature measures including
60 Chapter 4: Correction formula of infrared and conductive thermometry
rectal thermometers (Casa et al., 2007; Ganio et al., 2009; Mannara et al., 1993) and
ingestible temperature pills (Hunt and Stewart, 2008). This calibration of
thermometry devices at regular intervals has been shown to improve accuracy of
aging instruments and ensures their sensitivity and specificity is preserved for the
diagnosis of various conditions and pathologies (Machin, Simpson, & Broussely,
2009; Simpson, Machin, McEvoy, & Rusby, 2006; Wood, Mangum, Filliben, &
Tillett, 1978).
In contrast, infrared 𝑇sk devices (infrared video cameras and infrared
thermometers) are calibrated against a blackbody source (Foto et al., 2007).
However, these devices are often made to test temperatures outside the human
physiological 𝑇sk range and are typically in excess the budget of most researchers
and clinicians. This expense has seen researchers develop novel and more affordable
means of calibration for infrared techniques (Hetsroni, Gurevich, Mosyak, &
Rozenblit, 2003; Horwitz, 1999; Ochs, Horbach, Schulz, Koch, & Bauer, 2009).
Consequently, researchers have used stirred water baths for the calibration of
infrared devices prior to human thermoregulatory investigations (Buono et al., 2007;
D. Ng et al., 2005; Plassmann, Ring, & Jones, 2006). Therefore, the purposes of this
investigation were to i) compare and contrast the validity of four commonly used
contact and infrared devices in a stirred water bath, ii) to develop a calibration
coefficient for all devices to improve measurement accuracy in the assessment of
their interchangeability for human 𝑇sk measurements (see Chapter 5), and iii) to
identify the most accurate device to use as a comparative standard for a human skin
temperature investigation (see Chapter 5).
4.2 METHODS
4.2.1 Experimental overview
Four devices, two conductive and two infrared, were calibrated against a
certified thermometer (ThermoProbe Inc., Pearl, Mississippi, USA). The
thermometer, which was suspended in the water bath, served to compare the devices
against a reference standard (Hunt & Stewart, 2008). The conductive devices
included eight thermistors (TM) (Grant Instruments, Cambridge, UK) and eight
iButtons® (IB) (Maxim Intergrated, Sunnyvale, California, USA) and the infrared
devices included a hand held thermometer (IT) (Tecnimed Inc., Varese, Italy) and a
Chapter 4: Correction formula of infrared and conductive thermometry 61
thermal imaging camera (IC) (FLIR Systems, Wilsonville, Oregon, USA). Detailed
information regarding the specifications of all devices is presented in Table 4.1.
Table 4.1.
Device specifications
IR = Infrared. All specifications were derived from the corresponding company websites: a = http://www.thermoprobe.net/docs/data_TL1W.pdf; b = http://www.grantinstruments.com/media/5118/temperature_and_humidity_probes_june_2011.pdf; c = http://datasheets.maximintegrated.com/en/ds/DS1922L-DS1922T.pdf; d = http://www.flir.com/cs/emea/en/view/?id=41966; e = http://www.visiofocus.com/specificheEN.html.
A circulating water bath was used to test devices across eleven water
temperatures that encompassed the human skin physiological range (22, 24, 26, 28,
30, 32, 34, 36, 38, 40, 42 °C). This temperature range was selected to represent the
lowest expected ‘normal’ resting 𝑇sk in a thermoneutral environment (Niu et al.,
2001; Zaproudina et al., 2008), through to the upper range of 𝑇sk during exercise and
internationally standardised occupational limits (International Organisation for
Standardisation, 2004b). The temperature in the water bath was stabilised for at least
5-min before all devices simultaneously measure temperatures at 10-second intervals
for 1-min (Hunt & Stewart, 2008; Jutte et al., 2008; Long et al., 2010). These seven
values were later averaged for statistical analysis in accordance with previous work
(Hunt & Stewart, 2008). The temperature variation in the water bath was less than
0.02 °C during recording; a level of variation similar to that previously reported
Device Certified Thermometer
Thermistor (Data Logger)
iButton® Infrared Camera Infrared Thermometer
Model TL1-W
EU-UU-VL5-0 (SQ2020-2F8)
DS1922L-F50 A305 sc Visiofocus 06400
Make ThermoProbea
Grant Instrumentsb
Maxim Integratedc FLIR Systemsd Tecnimede
Specifications
Range:
Sensitivity:
Uncertainty:
-10 to +160 °C
0.01 °C
±0.06 °C
-50 to +150 °C
0.01 °C
±0.1 °C
-40 to +80 °C
0.0625 °C
±0.5 °C
IR Resolution:
Spectral Range:
-20 to +350 °C
<0.05 °C
±2 °C
320 x 240 pixels
7.5-14 µm
+1 to +55 °C
0.1 °C
±0.3 at 20-35.9 °C ±0.2 at 36-39 °C ±0.3 at 39.1- 42.5 °C ±1.0 at 42.6-55 °C
62 Chapter 4: Correction formula of infrared and conductive thermometry
(<0.025 °C and <0.05 °C) in the literature (Harper Smith et al., 2010; van Marken
Lichtenbelt et al., 2006). All testing was completed on the same day in a temperature
controlled room (22.7 ± 0.2 °C, 49.7 ± 3.3 % relative humidity and air speed <1 m/s)
which was illuminated by minimal LED lighting. The room was free of any electric
heat generators, wind drafts or external radiation (e.g., sunlight) which has been
reported to alter the accuracy of these devices (Ammer & Ring, 2005; Hildebrandt et
al., 2010).
4.2.2 Measurement Devices and Procedures
Thermistors
All available conductive devices found in our laboratory were used (8 TM’s
and 8 IB’s) to measure inter-device variability and to identify any defective devices.
The eight TM’s were connected to a data logger (Grant Instruments, Cambridge,
UK) that had its real-time clock synchronised with a laptop computer and IB’s. The
data logger was programmed to log the temperature every 10-seconds before
immersion. In preparation for testing the wires of the eight TM’s were taped over the
walls of a circulating water bath allowing the probes to hang submerged at an angle
of ~45°, ~2 cm from the bottom of the water bath. All immersed devices, including
the certified thermometer, were at least 1 cm apart and free from contact with the
shell of the water bath and each other, allowing water to flow freely around the
devices.
iButtons®
All eight IB’s were programmed prior to data collection to log every 10-
seconds at a resolution of 0.0625 °C via the accompanying USB to computer
receptor (DS9490R USB Port Adapter, DS1402D-DR8 Blue Dot Receptor, Maxim
Intergrated, USA). Once programmed each of the eight IB’s were suspended in water
by a length of sewing thread (300dtex, Sew-All Thread, Gütermann, Gutach im
Breisgau, Germany) tied around the circumference of the device, maintaining a set
distance of ~2 cm from the bottom of the water bath. Following the completion of
data recording the TM’s and IB’s were removed from the water bath, to terminate
logging and import the data to Microsoft Excel (Microsoft Office Professional Plus
2010, Microsoft, Redmond, Washington, USA).
Chapter 4: Correction formula of infrared and conductive thermometry 63
Infrared Camera
Two investigators simultaneously recorded data from the IT and IC manually.
This mirrored the recordings in the submerged contact devices. The IC was
positioned on a tripod directly above and perpendicular to the surface of the water.
Due to fluctuations in the cameras internal sensors (Grgić & Pušnik, 2011; Ring et
al., 2007), the IC was allowed to stabilise for 60-min before measurements.
Distances from the water surface were controlled at 60 cm. The camera was
connected to a second time-synchronised laptop computer that was running FLIR
R&D software (version 3.4.13191.2001, FLIR Systems, Wilsonville, Oregon, USA).
Emissivity for the IC was manually set to 0.99, resembling that of water (Rees &
James, 1992). All of the post-processing analysis associated with the IC was
completed by the same trained investigator using the aforementioned software.
Infrared Thermometer
The IT was an affordable, commonly used, point and shoot device with an
internally set emissivity depending on the desired measurement surface (e.g., water,
human skin). The second investigator took measurements every 10-seconds
simultaneously with the other devices and manually recorded values from the devices
digital display. The IT was secured at a constant distance of 60 mm from the surface
of the water. Readings from both infrared devices were taken adjacent to the areas
surrounding the submerged contact devices to ensure only the water temperature, and
not the contact devices were measured.
4.2.3 Statistical Analysis
The difference between each device and the certified thermometer was
calculated. Bland-Altman plots were used to compare these differences against the
certified thermometer. Mean differences (MD), 95% confidence intervals (CI) and
limits of agreement (LoA) between devices and the certified thermometer were
calculated using the following equations:
MD = �∑ xn� − �
∑ CTn
�
where MD is mean difference, ∑x is sum of the devices recorded temperatures, ∑CT
is the sum of the certified thermometers temperatures and n is the number of
recorded temperatures (n=7);
64 Chapter 4: Correction formula of infrared and conductive thermometry
CI = MD ± (1.96 ∙ SE)
where CI is 95% confidence interval, SE is standard error;
LoA = MD ± (1.96 ∙ SD)
where LoA is limits of agreement, SD is standard deviation.
Corresponding with maximum clinical significance (Joly & Weil, 1969;
Kelechi et al., 2011; Kelechi et al., 2006; Selfe et al., 2008), mean differences
between a device and the certified thermometer at a given temperature >0.5 °C were
classified as invalid. The device which recorded the lowest mean differences
compared to the certified thermometer across the range of tested temperatures was
classified as the most agreeable device.
Linear regression was conducted to determine the calibration formula for future
use in the human testing investigation (Chapter 5). R values are also reported in
Table 4.3, with categories used to interpret the r values described as: 0 = zero
correlation; 0.1 to 0.3 = weak correlation; 0.4 to 0.6 = moderate correlation; 0.7 to
0.9 = strong correlation; 1.0 = perfect correlation (Dancey & Reidy, 2007). For
demonstration purposes Bland-Altman plots for both contact devices were derived
from the least accurate from the eight respective samples; thermistor #5 (Figure 4.1a)
and iButton® #7 (Figure 4.1b) and analysed using SPSS (SPSS version 21.0, SPSS
Inc., Chicago, USA).
4.3 RESULTS
Mean differences, confidence intervals and limits of agreement between each
device and the certified thermometer across all temperatures are presented in Table
4.2. The mean differences ± standard deviation between the eight TM’s and the
certified thermometer were on average -0.03 ± 0.04 °C (range: 0.01 to -0.09 °C); the
eight IB were on average 0.23 ± 0.04 °C (range: 0.17 to 0.29 °C). While the IT and
IC recorded mean differences of -0.38 and 0.61 °C respectively. Limits of agreement
for the worst performing TM were -0.15 to -0.04 °C; 0.26 to 0.31 °C for the worst
performing IB; -0.92 to 0.15 °C for the IT and 0.44 to 0.78 °C for the IC (Table 4.2).
Independent calibration was conducted in order to define corrections formula,
based on linear regression, for each device. The TM slope calibration coefficients
averaged 1.003 ± 0.001 °C (range: 1.002 to 1.005 °C), the intercept averaged 0.08 ±
Chapter 4: Correction formula of infrared and conductive thermometry 65
0.03 °C (range: 0.04 to 0.13 °C), and all Pearson correlations coefficients (r)
equalled 1. The IB slope calibration coefficients averaged 1.001 ± 0.002°C (range:
0.999 to 1.005 °C), the intercept averaged 0.27 ± 0.07 °C (range: 0.2 to 0.41 °C), and
all r values equalled 1. The slope, intercept and r were 1.042, 0.94, 1.0; and 1.01,
0.95, 0.999 for both the IT and IC respectively. The individual linear regression
formula and r values are presented in Table 4.3.
Chapter 4: Correction formula of infrared and conductive thermometry 66
Figure 4.1. Bland–Altman plot of the certified thermometer and a) thermistor 5; b) iButton® 7; c) infrared thermometer; d) infrared camera across eleven water bath temperatures. Solid black line indicates the mean difference (MD); dashed lines represent the 95% limits of agreement (LoA).
Chapter 4: Correction formula of infrared and conductive thermometry 67
Table 4.2.
Mean difference and measures of variation for all tested contact sensors in
comparison to the certified thermometer.
Device MDa (°C) SDb SEc Upper CId Lower CId Upper LoAe
Lower LoAe
TM 1 -0.05 0.02 0.01 -0.03 -0.06 0.00 -0.10 2 -0.01 0.02 0.01 0.01 -0.02 0.04 -0.06 3 0.01 0.01 0.00 0.02 0.00 0.04 -0.02 4 -0.03 0.02 0.00 -0.02 -0.04 0.00 -0.06 5 -0.09 0.03 0.01 -0.07 -0.11 -0.04 -0.15 6 -0.03 0.03 0.01 -0.02 -0.05 0.02 -0.09 7 0.03 0.02 0.01 0.04 0.01 0.07 -0.01 8 -0.08 0.03 0.01 -0.06 0.10 -0.01 -0.14
IB 1 0.23 0.01 0.00 0.24 0.22 0.25 0.21 2 0.21 0.02 0.01 0.22 0.20 0.25 0.18 3 0.17 0.01 0.00 0.18 0.16 0.20 0.14 4 0.26 0.03 0.01 0.29 0.24 0.33 0.20 5 0.22 0.02 0.01 0.24 0.21 0.26 0.19 6 0.21 0.02 0.01 0.22 0.19 0.25 0.17 7 0.29 0.01 0.00 0.30 0.28 0.31 0.26 8 0.21 0.02 0.01 0.23 0.20 0.25 0.18
IT -0.38 0.27 0.10 -0.20 -0.57 0.15 -0.92 IC 0.61 0.09 0.03 0.67 0.55 0.78 0.44
TM = Thermistor; IB = iButton®. Devices with bolded numbers were selected for
human investigation (Chapter 5): 1 = Neck; 2 = Scapular; 3 = Hand; 4 = Shin a MD: Mean difference. b SD: standard deviation of mean difference. c SE: standard error of mean difference. d CI: 95% confidence interval. e LoA: 95% Limits of Agreement.
68 Chapter 4: Correction formula of infrared and conductive thermometry
Table 4.3.
Calibration formula for all devices.
Device MD (°C) Regression Formula r
TM 1 -0.05 𝑦 = 1.0033𝑥 – 0.0586 1.0 2 -0.01 𝑦 = 1.0034𝑥 – 0.1036 1.0 3 0.01 𝑦 = 1.0019𝑥 – 0.0679 1.0 4 -0.03 𝑦 = 1.002𝑥 – 0.0371 1.0 5 -0.09 𝑦 = 1.0042𝑥 – 0.04119 1.0 6 -0.03 𝑦 = 1.0039𝑥 – 0.0894 1.0 7 0.03 𝑦 = 1.0031𝑥 – 0.1305 1.0 8 -0.08 𝑦 = 1.0048𝑥 – 0.0764 1.0
IB 1 0.23 𝑦 = 0.999𝑥 – 0.1953 1.0 2 0.21 𝑦 = 1.0012𝑥 – 0.2518 1.0 3 0.17 𝑦 = 1.001𝑥 – 0.2048 1.0 4 0.26 𝑦 = 1.0046𝑥 – 0.4121 1.0 5 0.22 𝑦 = 1.001𝑥 – 0.2551 1.0 6 0.21 𝑦 = 1.0018𝑥 – 0.2678 1.0 7 0.29 𝑦 = 1.0𝑥 – 0.2877 1.0 8 0.21 𝑦 = 1.0014𝑥 – 0.258 1.0
IT -0.38 𝑦 = 1.0418𝑥 – 0.9388 1.0 IC 0.61 𝑦 = 1.0103𝑥 – 0.9461 0.9999
TM = Thermistor; IB = iButton®; MD = Mean Difference. Devices with bolded
numbers were selected for human investigation (Chapter 5). The following numbered
devices were used on the corresponding site through all human investigations
(Chapter 5): 1 = Neck; 2 = Scapular; 3 = Hand; 4 = Shin.
4.4 DISCUSSION
The objective of this study was to determine the validity of four commonly
used contact and infrared devices. Further to this we aimed to develop calibration
coefficients for all devices to improve measurement accuracy in the assessment of
their interchangeability for human 𝑇sk measurements (Chapter 5) and to identify the
most accurate device to use as a comparative standard for the human investigation
(Chapter 5).
To the best of our knowledge this is the first investigation that tested the
validity of four devices (two conductive and two infrared) commonly employed in
the assessment of 𝑇sk against a certified thermometer in a water bath. The key
Chapter 4: Correction formula of infrared and conductive thermometry 69
findings of this study show conductive devices are valid against a certified
thermometer and that infrared devices were approaching (infrared thermometer) or
greater than (infrared camera) the outlined minimal clinical significance (>0.5 °C).
These results suggest that the infrared devices used in this study may be an
inaccurate means of calculating 𝑇sk without prior calibration.
Thermistors and iButtons®
Mean differences of the TM’s and IB’s support the results of previous
investigations for similar devices (Harper Smith et al., 2010; van Marken Lichtenbelt
et al., 2006). Harper Smith et al. (2010) conducted an experiment with 28 TM’s and
46 IB’s comparing measurement differences against a certified thermometer in a
water bath. Mean differences between the TM’s, IB’s and the certified thermometer
were significantly different, 0.045 °C and 0.121 °C respectively. Although these
differences were statistically significant (P < 0.05), clinical significance (>0.5 °C)
was not breached. In the present study, differences between worst performing TM
and IB and the certified thermometer were not clinically significant, 0.094 °C and
0.288 °C respectively. Results indicate that the TM is the most accurate device tested
against the certified thermometer, and therefore has been identified as the most
appropriate comparative device for human skin investigation (Chapter 5).
Infrared Thermometer and Infrared Camera
Previous investigations measuring water bath surface temperature with IT’s
have found mean differences to be as high as 2 °C (D. Ng et al., 2005). The current
investigation found that the handheld IT measured temperatures within its
manufacturer claimed error between 22 and 30 °C (±0.3 °C between 20 and 35.9 °C).
Yet as water bath temperatures exceeded 32 °C, the uncertainty surpassed
manufacturer claims (±0.2 °C between 36 and 39 °C; ±0.3 °C at 39.1 and 42.5 °C)
and approached 0.8 °C between 36 to 42 °C. Measurement error increased linearly
with temperature, and was greatest at the upper limit tested (42 °C). This is of
particular concern as during real world applications, accuracy is essential at these
higher physiological temperatures where the risk of infection, inflammation, heat
illness or injury is greatest.
The IC had a manufacturer uncertainty of ±2 °C, which is approximately 20%
of the human 𝑇sk continuum from thermoneutral rest (~20 °C) through to the safe
limits in hot environments (43 °C). This suggests thermal cameras with similar
70 Chapter 4: Correction formula of infrared and conductive thermometry
manufacturer uncertainty might not be sufficient for human applications without
calibration prior to data collection. In this study, the IC’s mean difference was 0.61 ±
0.09 °C and was consistently reproduced across all temperatures. This error was
within the manufacturer claimed accuracy but exceeded clinical significance.
4.4.1 Limitations and Future Research
Despite water bath calibration being widely used as a calibration technique for
contact 𝑇sk instruments, the conductivity and heat capacity of water is greater than
that of the human skin. In addition, during human tissue measurements only a portion
of the device is in contact with the skin as opposed to being completely immersed in
the water bath. Consequently, although our findings show each of the conductive
instruments are valid, both of these factors could reduce the mean difference scores.
In relation to the infrared devices, despite both being marketed with capabilities to
measure water temperatures, the influence of water vapour evaporating off the
measurement surface is currently unknown. Although the effect of water vapour on
infrared measurements is unlikely as both positive and negative mean biases were
observed for each of the infrared devices. Future studies should compare any
potential differences in calibration factors for infrared devices derived from both
certified water baths and black body devices.
It should also be noted that only four types of devices were tested and our
findings might not be applicable to the all makes and models of skin measurement
instrumentation on the market. Conclusions drawn from this study could also be
affected by the small sample tested of each type of device. However, it would not be
feasible to purchase multiple, expensive infrared devices and the purpose of this
study was to examine the most commonly used in a clinical/research setting.
Further investigation is necessary to determine any differences between
conductive and infrared devices when applied to human skin, and what influences
temperature differences between devices during cold and heat exposure,
thermoneutral, exercise and recovery conditions (see Chapter 5).
4.5 CONCLUSION
Overall, conductive temperature devices tested in this study were validated
against a certified thermometer. However, infrared devices were not validated
against the certified thermometer. These findings justified the calibration of all types
Chapter 4: Correction formula of infrared and conductive thermometry 71
of the devices against a certified thermometer through the expected physiological
range of 𝑇sk before experimental data collection. The TM was classified as the most
accurate device and subsequently will be used as the comparative device for Chapter
5.
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 73
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
5.1 INTRODUCTION
The measurement of human thermoregulatory responses to environmental
extremes and exercise is of great interest to health professionals and researchers.
Historically, the measurement of human skin temperature (𝑇sk) via contact
(conductive) devices has been widely regarded as the primary measurement
technique in clinical, exercise science and research settings. However, contact
methods of 𝑇sk measurement present researchers with a number of potential
methodological limitations including: wire entanglement (van Marken Lichtenbelt et
al., 2006), loss of sensor contact during exercise (Buono et al., 2007), the formation
of a microenvironment around the sensor as a result of fixation method (Buono &
Ulrich, 1998; Tyler, 2011) and spot measurements (Costello, McInerney, et al.,
2012). The advent of more innovative non-contact technology has seen infrared
devices (e.g., handheld infrared thermometers and infrared cameras) become widely
accepted as techniques of assessing 𝑇sk in an attempt to overcome some of the
limitations associated with contact devices (Costello et al., 2013; Kelechi et al.,
2006; E. Ng, 2009).
To be considered clinically interchangeable mean differences between two
calibrated skin temperature instruments cannot exceed 0.5 °C (Joly & Weil, 1969;
Kelechi et al., 2011; Kelechi et al., 2006; Selfe et al., 2008). Unfortunately, despite
widespread use throughout clinical and research settings, the scientific evidence
supporting the interchangeability of infrared thermometry with more traditional
conductive instruments is limited and equivocal (Buono et al., 2007; Burnham et al.,
2006; Edge & Morgan, 1993; Hershler, Conine, Nunn, & Hannay, 1992; Kelechi et
al., 2011; Korukçu & Kilic, 2009; Matsukawa et al., 2000; Roy et al., 2006b; Ruopsa
et al., 2009; van den Heuvel et al., 2003).
74 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
Few studies have compared the interchangeability between different
conductive devices during exercise in varying ambient conditions (Harper Smith et
al., 2010; van Marken Lichtenbelt et al., 2006). However, comparisons between
contact and non-contact devices during exercise have been largely neglected with
only two investigations comparing devices during rest and exercise (Buono et al.,
2007; Fernandes et al., 2014); with a single study measuring the effect of varying
ambient temperatures on device accuracy (Buono et al., 2007). Buono et al. (2007)
surmised that infrared thermometry is a valid means to measure mean skin
temperature (𝑇�sk) in rest and exercise in both hot and cold environments. However,
these suggestions were based on a comparison between thermistors and an infrared
thermometer. In addition, 𝑇�sk was not measured during participant recovery post
exercise. In a more recent study by Fernandes et al. (2014) recovery of 𝑇�sk from
exercise under thermoneutral conditions was evaluated with both an IC and TC’s.
Differences between the IC and TC’s were significant during rest (0.75 ± 0.39 °C),
exercise (-1.22 ± 0.7 °C) and recovery (1.16 ± 0.66 °C) with the authors concluding
that there is poor correlation and low-reliability between the two measurement
modalities.
To our knowledge, no study has examined a range of devices commonly used
to assess 𝑇�sk during exercise in a hot and humid environment and post-exercise
recovery. Therefore, the purpose of this study was to systematically evaluate the
interchangeability of four devices – two conductive (thermistors [TM] and iButtons®
[IB]) and two infrared (infrared thermometer [IT] and infrared camera [IC]) – in the
assessment of 𝑇�sk during rest, exercise in the heat and subsequent recovery. It was
hypothesised that under all conditions, the conductive and infrared devices tested
would be considered clinically interchangeable (error ≤0.5 °C) with the comparative
thermistor.
5.2 METHODS
5.2.1 Participants
After ethical approval from the Human Research Ethics Committee
(Queensland University of Technology) (Appendix A) a convenience sample of 30
healthy males participated in this study. Prior to commencing the study all
participants completed a health screen questionnaire (Appendix B) and provided
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 75
signed informed consent (Appendix C). Contraindications for participation included
a history, or current existence of any cardiopulmonary disease, acute skin conditions
(e.g. adhesive allergy), any metabolic, arterial, venous or lymphatic pathology,
current history of smoking, or the use of any medication that alters cardiovascular
function or thermoregulation.
Participant demographic and anthropometric characteristics are presented in
Table 5.1. Height was measured with a stadiometer to the nearest 5 mm, with shoes
removed in an upright posture and during inhalation. Digital scales (Wedderburn
BWB-600, Tanita Corporation, Tokyo, Japan) were used to measure body mass to
the nearest 50 grams. An International Society for the Advancement of
Kinanthropometry (ISAK) accredited examiner recorded the sum of skinfolds taken
at 8 anatomical locations on the right hand side of the body (tricep, sub scapular,
bicep, iliac crest, supraspinale, abdominal, front thigh, medial calf) using a
Harpenden skinfold caliper (British Indicators Ltd, Weybridge, UK). All measures
were duplicated with the average of the two measurements representing the site; with
a third measurement taken if differences between the first two values were greater
than 5%.
Table 5.1.
Participant characteristics, values are mean ± standard deviation (range).
Age (years) Body Mass (kg) Height (cm) ∑ of 8 Skin Folds (mm) BMI (kg·m-2)
25.0 ± 2.9 (18.7 - 32.8)
78.7 ± 11.4 (50.8 - 113.2)
181.3 ± 8.3 (168.0 - 208.9)
88.94 ± 32.3 (41.1 - 145.3)
23.9 ± 2.2 (17.6 - 28.5)
BMI: Body mass index.
5.2.2 Pre-experimental Protocol
Participants were instructed to avoid prolonged sun exposure five days prior to
the testing day (to prevent sunburn). Where appropriate, any measurement site with
exposed hair was shaved at least 36 hours before testing, to prevent inflammation or
damage to the skin surface from the razor artificially raising skin temperature (Merla
et al., 2010). To ensure compliance participants were contacted two days prior to
testing. On the day of testing participants were required to keep the measurement
sites clean of ointments and cosmetics. In preparation for testing participants did not
engage in exercise, ingest caffeine or alcohol 24 hours prior to testing (Ammer &
Ring, 2006); or have a hot shower within two hours of arriving to the laboratory.
76 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
Two hours before the trial commenced, participants were asked to consume a light
meal with 500 mL of water. Clothing was instructed to be unencumbering and
conducive to exercise.
5.2.3 Experimental Protocol
All testing took place in a sub-tropical location in Australia’s Spring season
(September and October), beginning at either 0900 h or 1400 h and lasted
approximately three hours. Volunteers entered the controlled laboratory from
outdoor temperatures of 23.1 ± 2.0 °C and 58 ± 10 % relative humidity at 0900 h and
25.8 ± 2.1 °C and 51 ± 9 % relative humidity at 1400 h. The primary outcome in the
current study was within subject variation in the four devices. We were not interested
in between subject variability and therefore, different time of day was not considered
a confounder in the analysis.
Upon arrival the testing protocol was explained to all participants, any
questions were answered, and informed verbal and written consent was acquired
(Appendix C). Initially the four skin temperature measurement sites (Figure 5.1)
were cleaned with rubbing alcohol to remove any oils or other residual contaminants
influencing skin emissivity (Bernard et al., 2013). During environmental acclimation
and data collection participants wore only training shoes, socks, shorts and a heart
rate monitor.
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 77
Figure 5.1. Four skin temperature measurement regions of interest in accordance with International Organisation for Standardisation - 9886. 1) back of neck; 2)
inferior border of right scapula; 3) dorsal right hand; 4) proximal third of right tibia.
Data collection consisted of repeated 𝑇sk measurements taken by four
commonly used instruments (Table 5.2), during three sequential periods of rest,
exercise in the heat and recovery (Figure 5.2). Acclimatisation, resting and recovery
took place in a temperature controlled, fluorescently lit room without the existence of
electric heat generators, wind drafts or external radiation (i.e. sunlight). The exercise
protocol was completed in a climate chamber (dimensions 4 x 3 x 2.5m; length,
width, height). Skin temperatures, ambient temperature and relative humidity (with
digital weather station: 3M QuestTEMP 36, 3M, St. Paul, Minnesota, United States),
and air speed (with digital anemometer: Kestrel Pocket Weather 4000, Nielsen-
Kellerman, Boothwyn, Pennsylvania, USA) were measured at 3 minute intervals
during rest, exercise and recovery periods.
78 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
Figure 5.2. Timeline of data collection protocol. 𝑇�sk = Mean Skin Temperature; TM
= Thermistor; IB = iButton®; IT = Infrared Thermometer; IC = Infrared Camera.
Rest
Following a conventional 20-min acclimatisation (Hart & Owens Jr, 2004; Roy
et al., 2006a), resting measurements were taken during 30-min of seated rest in a
thermoneutral environment (24.0 ± 1.3 °C, 56 ± 9 % relative humidity, <0.1 m/s air
speed). Participants were seated on an adjustable stool for the duration of the
acclimatisation, resting and recovery periods. Seated position consisted of an upright
posture, feet flat on the floor, forearms resting on the thighs and the head consistent
with the Frankfurt plane. At the beginning of the acclimatisation period and at the
commencement of exercise, participants were given 250 mL of room temperature
water for a total fluid consumption of 500 mL.
Exercise
The exercise protocol was conducted on a Monark cycle ergometer (Ergomedic
824E, Monark, Vansbro, Sweden) with 1 kilogram loaded on a 500 g weighted
basket for a total resistance of 2.0 kg at 60 revolutions per minute (2.0 kp at 60
rev·min-1 = 120 watts). Ambient conditions were controlled at 38.0 ± 0.5 °C, 41 ± 2
% relative humidity and a wind speed of 0.5 ± 0.1 m/s. This type of condition was
chosen to induce large 𝑇sk changes and resembled similar investigations (Buono et
al., 2007; Harper Smith et al., 2010; van Marken Lichtenbelt et al., 2006). All
subjects were able to achieve this workload for the required 30-min.
Recovery
Following exercise, participants returned to seated rest in the thermoneutral
observation room (24.0 ± 1.3 °C, 56 ± 9 % relative humidity, <0.1 m/s air speed) for
45-min of data collection.
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 79
5.2.4 Measurements and Equipment:
Skin Temperature
Four measurement devices were used to assess skin temperature (Table 5.2);
two contact devices: thermistor (TM) (Grant Instruments, Cambridge, UK) and
iButton® (IB) (Maxim Intergrated, Sunnyvale, California, USA); and two non-
contact devices: infrared camera (IC) (Tecnimed Inc., Varese, Italy) and handheld
infrared thermometer (IT) (FLIR Systems, Wilsonville, Oregon, USA). The TM, IB
and IT were new, unused devices while the IC was serviced and calibrated by the
manufacturer prior to the commencement of this study. Additionally, all devices
were previously calibrated against a NIST-certified thermometer in a stirred water
bath before human investigation (Chapter 4). The resultant calibration formula was
applied to the recorded values following human data collection (see Chapter 4, Table
4.3).
80 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
Table 5.2.
Device specifications
IR = Infrared. All specifications were derived from the corresponding company websites: a = http://www.grantinstruments.com/media/5118/temperature_and_humidity_probes_june_2011.pdf; b = http://datasheets.maximintegrated.com/en/ds/DS1922L-DS1922T.pdf; c = http://www.flir.com/cs/emea/en/view/?id=41966; d = http://www.visiofocus.com/specificheEN.html.
Contact Devices
Because of minimal differences found within each of the TM and IB during
water bath calibration (Chapter 4) the first four of the eight calibrated devices were
selected for this investigation. The four TM were connected to an associated data
logger (Grant Instruments, Cambridge, UK) and laptop computer that was used to
time synchronise both the TM and IB. Before application to the participant the data
logger and four associated TM were preprogramed to log every 2-seconds. All IB
were pre-programmed via the accompanying USB to computer receptor
(DS9490R USB Port Adapter, DS1402D-DR8 Blue Dot Receptor, Maxim
Integrated, Sunnyvale, California, USA) and time synchronised with the TM to log
Device Thermistor (Data Logger)
iButton® Infrared Camera Infrared Thermometer
Model EU-UU-VL5-0 (SQ2020-2F8)
DS1922L-F50 A305 sc Visiofocus 06400
Make Grant Instrumentsa Maxim Integratedb FLIR Systemsc Tecnimedd
Specification Range:
Sensitivity: Uncertainty:
-50 to +150 °C 0.01 °C ±0.1 °C
-40 to +80 °C 0.0625 °C ±0.5 °C
IR Resolution:
Spectral Range:
-20 to +350 °C <0.05 °C ±2 °C 320 x 240 pixels 7.5-14 µm
+1 to +55 °C 0.1 °C ±0.3 at 20-35.9 °C ±0.2 at 36-39 °C ±0.3 at 39.1-42.5 °C ±1.0 at 42.6-55 °C
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 81
every 2-seconds at an 11-bit resolution of 0.0625 °C. Details regarding the
application of contact devices to the participants are discussed further in this section
under Regions of Interest. Once testing was completed, both the TM and IB were
removed from the participant to terminate logging and import all data into Microsoft
Excel (Microsoft Office Professional Plus 2010, Microsoft, Redmond, Washington,
USA).
Non-contact Devices
Infrared skin temperature measuments were taken by two researchers; one
recorded values from the infrared thermometer and the other the infrared camera
measures. The IT is a relatively cheap, point and shoot device commonly employed
in clinical settings. For measurements the IT was held 90° from the skin’s surface
with the aid of spacing rods that were added to the casing of the device (Roy et al.,
2006b). This kept the device at a constant distance of 60 mm from the skin. The
device was equipped with a manual internal re-calibration for large changes in
ambient temperatures. When moving between thermoneutral to hot, and hot to
thermoneutral conditions, the IT was re-calibrated to the ambient conditions prior to
any readings. During exercise on the bike, one researcher measured the temperatures
at each of the four skin sites within a 15-second period. While the other researcher
recorded the time (hh:mm:ss) of each recording, to ensure accurate comparison to
logging contact devices. During the shin regions temperature measurement
participants were asked to stop pedalling (approximately 3 to 5-seconds) so the IT
could record the site temperature.
The IC was set up on a level tripod perpendicular to the seated, resting
participant at a distance of approximately 0.8 to 1.1 m depending on the height and
size of the participant (Ammer, 2003, 2008; Ammer & Ring, 2006). The camera was
set up and allowed to stabilise for at least 60-min prior to subject arrival (Grgić &
Pušnik, 2011). Any required adjustments needed to fit the regions of interest within
the IC field of view resulted from the manipulation of chair height and its distance
from the camera. In order to assure high quality images, auto-focusing of the
camera’s field of view was performed prior to the capture of each thermal image.
Each image was time stamped for accurate post-processing of images. Post-
processing FLIR R&D software (version 3.4.13191.2001, FLIR Systems,
Wilsonville, Oregon, USA) was used to input recorded variables such as ambient
82 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
temperature, relative humidity, camera distance and a constant skin emissivity of ε =
0.98 in accordance with previous research (Boylan et al., 1992; Sanchez-Marin et al.,
2009; Steketee, 1973; Togawa, 1989). The selection of the region of interest was
made with the variable rectangle tool to select all pixels within the distinct area
outlined by the aluminium tape (see Regions of Interest).
𝑇�sk was derived from three thermal images that encompassed four regions of
interest (Figure 5.3) taken within a 30-second period. The corresponding IT
measurement was taken by the second researcher simultaneously to the thermal
image at a given site. A stopwatch synchronised to the computer was used to ensure
manual recordings by researchers matched the autonomously logging contact
devices. The time of recordings (hh:mm:ss) were scribed for accurate retrospective
data extraction from the contact devices.
Methodological constraints prevented the use of the IC during exercise
conditions. These included potential measurement error from the camera by
physically moving it between each phase of testing, before adequate stabilisation
time of at least 30-min (Grgić & Pušnik, 2011). In addition, it seemed impractical to
require the subject to cease exercising and dismount from the cycle ergometer every
3-min to take the required photos. As a result, only the three other types of devices
were compared in the exercise condition.
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 83
Figure 5.3. Example of regions of interest captured via infrared thermography. a) Hand b) Neck and Scapula c) Shin.
Regions of Interest
Measurements were taken at four body locations (back of neck, inferior border
of right scapula, dorsal right hand and proximal third of right tibia) in accordance
with ISO 9886 (International Organisation for Standardisation, 2004b). The readings
from these sites were used to calculate 𝑇�sk using the following equation
(International Organisation for Standardisation, 2004b): 𝑇�sk = (Tneck*0.28) + (Tscapula*0.28) + (Thand*0.16) + (Tshin*0.28)
Where Tneck represents the skin temperature (°C) of that region and the
numerical value (e.g. 0.28) is the weighted value applied to that site.
A square template marking the placement of devices was drawn on the skin at
each of the four skin temperature sites (Figure 5.4a). Within the marked square were
four 25 mm x 25 mm quadrants, with each representing a measurement site for one
of the four devices (Figure 5.4b). In order to account for any within site variation,
84 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
device allocation within a given quadrant was determined with a random number
generator.
Figure 5.4. a) Diagram of template dimensions used on each of the four skin sites; b) example of the randomised layout of marked and placed devices on a male subject’s shin; IB: iButton®, IT: Infrared Thermometer, TM: Thermistor, IC: Infrared Camera.
To maintain reliable placement of the contact devices to the skin, the same
researcher marked the region of interest and positioned the devices for each subject.
Throughout experimental testing, each contact device was marked with one of the
four sites (e.g. neck) and constantly placed upon the same site for each participant.
Contact devices were held in place with a single layer of Leuko sportstape
(Leuko, Beiersdorf, Hamburg, Germany) to reduce the influence of tape artificially
increasing temperatures (Buono & Ulrich, 1998; Tyler, 2011). Four 3 mm x 50 mm
strips of aluminium tape (3M, St. Paul, Minnesota, United States) were used as inert
markers and placed around the infrared camera quadrant to identify the region of
interest during post processing of the thermal images (Figure 5.4b).
5.2.5 Statistical Analysis
The data are displayed as mean ± SD unless otherwise stated. The response of
all devices was similar regardless of the measurement site and therefore, for the
purpose of this study 𝑇�sk was primary site for analysis (the complete graphed data set
is presented in Appendix D). Repeated measures analysis of variance (ANOVA) was
used to assess the effect of time, device, and device by time for all measured sites
and skin temperature (all outputs presented in Appendix E). All variables were tested
for normality via Shapiro-Wilks tests and where the assumption of sphericity was
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 85
violated, the Greenhouse-Geisser epsilon was used to adjust the degrees of freedom
to increase the critical values of the F-ratio. Statistical significance for the ANOVA
was set to P < 0.05.
Paired samples t-tests post-hoc analysis, using a Bonferroni correction, were
performed where significant differences between device and time were identified for
𝑇�sk across all three periods. Time points were selected for the beginning, middle and
end of the resting period, and every second time point from the start of the exercise
and recovery periods. Without the presence of a gold standard for skin temperature
measurement, the TM was used as the comparative device in which differences
between all other devices were tested (outputs and comparisons between all devices
are presented in Appendix F). The TM was identified as the comparative device for
this investigation was due to its performance against the certified thermometer in the
previous water bath calibration (Chapter 4). All data was analysed using SPSS (SPSS
version 21.0, SPSS Inc., Chicago, USA).
5.3 RESULTS
A significant main effect for device by time was observed in all three periods
for 𝑇�sk (Rest: F30,870=2.734, P=0.004, 1-β=0.96; Exercise: F20,580=155.54, P < 0.001,
1-β=1.00 and Recovery: F30,870=125.08, P < 0.001, 1-β=1.00). Pairwise comparisons
of 𝑇�sk revealed significant differences (P < 0.001) between TM and IT, and TM and
IC during resting conditions, and significant differences (P < 0.001) for comparisons
between the TM and all other devices tested during exercise and recovery. Mean
differences between TM and IB are as follows: rest = -0.01 °C, exercise = -0.25 °C,
recovery = -0.37 °C; the TM and IT: rest = -0.34 °C, exercise = 0.46 °C, recovery = -
1.04 °C; TM and IC: rest = -0.83 °C, recovery = -0.188 °C. Post-hoc analysis of
individual time points for clinical and statistical significance differences between the
TM and the other devices are indicated in Figure 5.5.
86 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
Figure 5.5. Mean skin temperature (n=30) of all tested devices during rest (4 devices), exercise (3 devices) and recovery (4 devices). a = IB clinically (>0.5 °C) and significantly (P < 0.001) different from TM; b = IT clinically (>0.5 °C) and significantly (P < 0.001) different from TM;
c = IC clinically (>0.5 °C) and significantly (P < 0.001) different from TM. TM: Thermistor; IB: iButton®; IT: Infrared Thermometer; IC: Infrared Camera.
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 87
5.4 DISCUSSION
The aim of this study was to evaluate 𝑇�sk differences measured by three
commonly used devices in comparison to a calibrated thermistor during rest, exercise
in the heat and passive recovery. It was hypothesised that under all conditions, the
conductive and infrared devices tested would be considered clinically
interchangeable (error ≤0.5 °C) with the comparative TM. Although comparisons
between 𝑇sk devices have been documented in the past (Buono et al., 2007; Burnham
et al., 2006; Harper Smith et al., 2010; Hershler et al., 1992; Kelechi et al., 2011;
Kelechi et al., 2006; Korukçu & Kilic, 2009; Matsukawa et al., 2000; Roy et al.,
2006b; Ruopsa et al., 2009; van den Heuvel et al., 2003; van Marken Lichtenbelt et
al., 2006), no study has systematically evaluated the interchangeability between
infrared and conductive instruments during rest, exercise and recovery. The key
findings of this study include: (1) the IC was not interchangeable with the
comparative TM device during rest or recovery; (2) it should not be assumed that
devices within acceptable agreement during resting conditions will continue to agree
during exercise and recovery; and (3) clear systematic errors exceeding statistical and
clinical (>0.5 °C) significance are present between conductive and infrared devices
throughout all conditions. These findings are in direct contrast to our hypothesis,
namely that infrared and conductive devices would not exceed clinical significance
under all conditions. For the purpose of this discussion comparisons between devices
will be covered separately for each of the three periods.
Rest
The present results indicate that 𝑇�sk measured by IC is significantly different to
that measured by TM’s, and with mean differences >0.5 °C the IC would not be
considered interchangeable under medical or scientific applications. Across all time
points measured during the rest period, even after calibration, the IC consistently
overestimated 𝑇�sk compared to the TM by an average of 0.83 ± 0.39 °C. Significant
differences preventing the interchangeability of IC and TM have been observed
previously (Fernandes et al., 2014; van den Heuval et al., 2003). However,
differences in the current study of 0.83 ± 0.39 °C are not consistent with the earlier
study by van den Heuvel et al. (2003), where a previously calibrated IC
underestimated 𝑇sk when compared to a TM, with mean differences of -2.32 ± 0.54
°C. Discrepancies between this previous study and the present investigation could be
88 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
explained by methodological differences such as data collection and instrument
makes/models. More specifically, in the study by van den Heuvel et al. (2003) 𝑇sk
was not recorded simultaneously. The thermistor values were averaged from a
recording frequency of 1 Hz over a 30 second period, while infrared camera images
were taken at a single time point within the same 30 second period. Furthermore, TM
were attached with a ‘minimal amount’ of collodion adhesive glue under the sensor
head and post image analysis selecting the skin ‘immediately adjacent’ to the TM tip.
In combination with any subjective variance for selecting this ‘adjacent area’
between repeated IC images during post processing analysis, any excess adhesive
dispersing outside of the TM tip could cause the IC to measure the temperature of the
adhesive on the skin and not the skin itself. In a more recent investigation, Fernandes
et al. (2014) found infrared camera overestimated 𝑇�sk measure by a thermocouple by
0.75 ± 0.39 °C during rest in a thermoneutral environment, which is similar to that of
the current investigation (0.83 °C). Nevertheless, in each study the IC would not be
considered interchangeable with more traditional conductive means of 𝑇sk
measurement under stable resting conditions as seen in clinical and research settings.
In contrast, satisfactory mean differences were observed between both the TM
and the IB, and the TM and the IT (Figure 5.5). Although others have reported
similar findings to the current study with differences between TM and IT of ≤0.5 °C
(Buono et al., 2007; Burnham et al., 2006; Hershler et al., 1992; Kelechi et al., 2011;
Kelechi et al., 2006), there have been studies approaching (Burnham et al., 2006;
Matsukawa et al., 2000) or exceeding (Roy et al., 2006b) clinical significance under
resting conditions. This investigation is the first to compare the IB against other 𝑇sk
devices in a resting stable thermoneutral (24 °C) environment. A similar study by
Harper Smith et al. (2010) compared IB’s to TM’s during rest and exercise in 10, 20
and 30 °C ambient temperatures with varying wind speeds. During the closest
comparative condition to our study (20 °C, 0.18 m/s), Harper Smith et al. (2010)
found that despite calibration, the IB’s mean differences between the IB and TM (0.7
± 0.02 °C) violated statistical and acceptable clinical limits. In the present
investigation, after individual calibration of devices, no clinical or significant
differences were found between the TM’s and IB’s under stable thermoneutral
conditions (mean differences of -0.01 ± 0.2 °C). One reason for this may be the
exposure to cooler ambient temperatures in the previous study. Additionally,
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 89
different methods of fixation and models of thermistors could potentially explain the
contrasting results.
Exercise
During exercise in the heat, considerable differences and temperature
fluctuations were observed between infrared and conductive measurement devices, in
contrast to our hypothesis. These differences are highlighted in Figure 5.5 with the IT
and IB’s differing in both clinical and statistical significance from the thermistor
temperatures at various points throughout exercise in the heat. Initial increases in 𝑇sk
while exercising in the heat are predominantly a function of ambient temperature and
are not significantly dependent upon workload (Stolwijk & Hardy, 1966). Therefore,
these initial differences observed between the three devices are most likely a result of
individual thermal inertia of the two conductive devices and the exposed skin
equilibrating to the change in ambient temperatures. The clinical and statistical
differences between the IB’s and TM’s at the start and towards the end of exercise
contradict previous observations (Harper Smith et al., 2010; Stolwijk & Hardy, 1966;
van Marken Lichtenbelt et al., 2006). We propose dissimilar findings could be due to
a number of factors. As a result of the high thermal strain involved in our study
(38°C, 40% relative humidity), it is likely that the skin of the participants became
saturated with sweat as testing progressed and the tape holding the conductive
devices in place absorbed the sweat, altering its evaporative and thermal conductivity
(Psikuta et al., 2013). The influence in which the sweat covered tape had on each
device would be a product of the shape, size and material properties (i.e. copper vs.
aluminium) of both TM’s and IB’s. The effect of sweat saturating the tape is best
illustrated during the recovery period whereby differences between each conductive
device equalise as the sweat evaporates during resting conditions (75–108th minute,
Figure 5.5).
Some evidence suggests that IT agrees sufficiently with traditional TM for the
measurement of 𝑇sk in the presence of environmental stressors (Buono et al., 2007;
Kelechi et al., 2011; Psikuta et al., 2013). This investigation found low agreement
and significant differences between the IT and TM’s during exercise in the heat. The
amplified differences seen between the infrared thermometer and thermistors as
exercise progressed may be a product of cooler sweat pooling and evaporating from
the surface of the skin. Consequently, this would likely prevent the IT from
90 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
measuring accurate skin temperatures (Bernard et al., 2013). Moreover, the
insulating characteristics of the tape covering the conductive devices would create an
insulating microenvironment, limit evaporative cooling and therefore increase the
temperature relative to the exposed infrared measurement site (Buono & Ulrich,
1998; Tyler, 2011).
Despite not measuring 𝑇�sk with the IC during the exercise period, it is logical
to suggest that the IC would have been significantly influenced by the presence of
sweat along the skin surface with relative changes comparable to that of the IT.
Recent findings by Fernandes et al. (2014) whereby an IC progressively
underestimated 𝑇�sk throughout exercise relative to the comparative thermocouples (-
1.22 ± 0.7 °C) supports our postulation. This effect has also been observed in IC in
which liquids present along the skin surface cause significant underestimation of true
skin temperatures (Bernard et al., 2013). Moreover, even if relative, and not absolute,
changes in 𝑇�sk are of interest to researchers and exercise scientists, the use of infrared
devices may not be suitable in settings where the participant is subjected to hot
environments or exercise that induces a sweating response. Future research should
determine the influence of confounding factors such as sweat on both infrared and
conductive devices, by measuring localised sweat rates (Ohhashi, Sakaguchi, &
Tsuda, 1998; Smith & Havenith, 2012) during both exercise and recovery.
Recovery
To the best of our knowledge this is the first investigation that has compared
infrared and conductive devices for the calculation of 𝑇�sk during recovery from
exercise in the heat. The present findings demonstrate systematic differences
between conductive and infrared means of 𝑇sk measurement (Figure 5.5). Statistical
and clinical differences are present between the TM and both infrared instruments
throughout the recovery period. The recovery phase saw the greatest mean
differences between TM and every other device (IB = -0.37 °C; IT = -1.04 °C; IC
-1.88 °C). Similar results for the IC were observed by Fernandes et al. (2014) during
recovery from exercise in a thermoneutral environment, with the IC over estimating
skin temperatures by 1.16 °C. Similar contrasting relative changes in skin
temperature during exercise and recovery between conductive and infrared devices
were reported by Fernandes et al. (2014) and denote clear distinctions between the
scientific principles underlying conduction and radiation. Iit is logical to suggest that
Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices 91
the presence of sweat as a result of exercise in the heat plays a significant role in the
measurement differences observed in the current study. Differences between
conductive and infrared devices are greatest following 18-min of rest. As the sweat
evaporates from the tape covering the conductive devices, 𝑇�sk begins to converge,
but fails to return to baseline values after 45-min. Findings from this investigation
suggest that conductive and infrared devices cannot be used interchangeably during
recovery from hot conditions and report similar results to that of recovery following
exercise in thermoneutral temperatures (Fernandes et al., 2014). This limits
comparisons between a large portion of the exercise science literature, where
thermoregulatory responses are depicted differently between means of cutaneous
temperature measurement. Future studies should determine if similar differences are
seen during recovery from cold exposure.
Limitations
Due to the conductive devices being in direct contact with the skin,
comparisons made between devices were measured from sites adjacent to each other
and not a single point on the skin. Skin temperature variation within the
measurement area could contribute to measurement differences between devices
(Frim et al., 1990). However this is unavoidable as contact devices must cover the
area of skin they are measuring. Furthermore, as there are no standardised anatomical
placements for 𝑇�sk devices within a region of interest, we feel the uniform
measurement area (50 mm x 50 mm) and the randomised allocation of devices within
the area minimised errors associated with variation across the site.
Unfortunately this study was not able to compare measured 𝑇�sk using the IC
during exercise due to methodical constraints. IC’s require stabilisation to the
surrounding ambient conditions for accurate measurement (Grgić & Pušnik, 2011)
and because of changes in testing environments during rest, exercise and recovery,
stabilisation would not have been possible. Additionally, it is impossible to attain 𝑇sk
across numerous measurement sites with a single IC during dynamic exercise. A
plausible solution would be to use multiple cameras in each environment and around
the participant during exercise. However due to the large cost associated with IC this
is not a realistic alternative.
92 Chapter 5: Mean skin temperature assessment during rest, exercise in the heat and recovery: differences between conductive and infrared devices
5.5 CONCLUSION
In conclusion, this investigation found that even after calibration, conductive
and infrared devices are not interchangeable under resting, exercise or recovery
conditions. More specifically, the IC consistently overestimated 𝑇sk outside clinical
and significant limits compared to the comparison TM. The results also indicate that
IB and IT are interchangeable with the TM under stable resting conditions. Though,
this interchangeability between the IT and TM is not maintained following exercise
in the heat or during recovery. It is proposed the presence of sweat results in
systematic errors between infrared and conductive devices due to the principles of
conductive and radiant heat measurement. It should be noted that the current findings
may not apply to all makes and models of skin thermometry, or to other ambient
conditions (e.g., cold exposure) or populations (e.g. elderly or females). In summary,
the current findings demonstrate that clinical and significant differences exist
between conductive and infrared devices which are commonly employed in the
assessment of human 𝑇sk.
Chapter 6: Conclusions 95
Chapter 6: Conclusions
Introduction
The primary aim of this thesis was to investigate the interchangeability of
conductive and infrared means of 𝑇sk measurement at rest in a thermoneutral
environment, during exercise in the heat and recovery (Chapter 5). Prior to the
investigation of this research question, a systematic review of the literature
pertaining to the interchangeability of conductive and infrared 𝑇sk devices (Chapter
3) was undertaken. The systematic review allowed for the objective development and
evaluation of a methodology that would appropriately answer this thesis’s primary
aim. This lead to a calibration study (Chapter 4) of four unique devices in order to
achieve two things: 1) to derive a correction formulae from devices against a
reference standard in a water bath, and 2) establish the most accurate of these four
devices to use as a comparative reference for the human investigation.
Findings
It was concluded in Chapter 3 that there were large limitations within the
current evidence base and it was unclear if devices were interchangeable in the
presence of external (e.g., exercise) or environmental stimuli (e.g., cold/heat
exposure).
In contrast to our null hypothesis in Chapter 4, clinically significant differences
were observed between infrared devices and the certified thermometer. In agreement
with the null hypothesis for Chapter 4, the thermistor was correctly identified as the
most accurate device compared to the certified thermometer in a water bath across
the expected physiological range, and was identified as the comparative device for
the subsequent 𝑇sk investigation (Chapter 5).
Findings of the 𝑇sk investigation suggest that even after calibration, conductive
and infrared devices are not interchangeable under resting, exercise or recovery
conditions for the measurement of 𝑇�sk. In addition, it should not be assumed that
devices within acceptable agreement during resting conditions will continue to agree
during exercise and recovery. In summary, the current findings demonstrate that
clinical and significant differences exist between conductive and infrared devices
96 Chapter 6: Conclusions
which are commonly employed in the assessment of human 𝑇sk in exercise science,
research and clinical settings.
Implications
These findings have important implications given the wide variety of
commercially available 𝑇sk measurement devices available to the public. Accurate
comparisons between publications using different 𝑇sk measurement methods may not
be possible under resting, exercise and high ambient conditions which elicit different
thermoregulatory responses. These significant differences between conductive and
infrared means could potentially influence the interpretation of results, diagnosis and
therefore treatment outcomes for clinical and exercise science applications.
Limitations
It should also be noted that only four types of devices were tested and our
findings might not be applicable to all the makes and models of skin measurement
instrumentation on the market. Calibration of conductive devices could have been
affected as the thermal conductivity and heat capacity of water is greater than that of
the human skin. Furthermore, during human testing (Chapter 5) only a portion of the
device is in contact with the skin, as opposed to being completely immersed in the
water bath (Chapter 4).
In regards to Chapter 5, due to the conductive devices being in direct contact
with the skin, comparisons made between devices were measured from sites adjacent
to each other and not a single point on the skin. Skin temperature variation within the
measurement area could contribute to measurement differences between devices.
However, this potential bias was diminished by randomly allocating devices within
the region of interest.
Future Research
Building upon the findings in Chapter 4, in order to determine if water vapour
influenced the calibration of infrared devices, it is recommended future studies
compare any potential differences in calibration formula for infrared devices derived
from both certified water baths and black body devices.
There is a lack of high quality investigations into the interchangeability of
commonly used skin temperature measurement devices. Moreover, the influence in
which interventions such as exercise or environmental stress has on measurement
Chapter 6: Conclusions 97
differences between devices has been largely ignored. Therefore, future research
should build upon the findings of the current study by assessing measurement
differences between devices during resting and exercise conditions (of differing
intensities and modalities) in a wider range of ambient temperatures (including cold
exposure). Further to this, greater understanding is required to determine whether
findings reported in this study can be applied to females, populations (young vs.
elderly; lean vs. obese) and/or ethnicities.
Appendices 99
Appendices
Appendix A Ethics Approval
100 Appendices
Appendix B Health Screen Questionnaire
Health Screen Questionnaire
Date / / Name
Sex Male Female D.O.B
Height Weight Resting Pulse
How are you feeling today? Well Unwell
Stage 1 - Medical Conditions
1. Have you in the past 18 months:
• Had any muscle or skeletal injuries No Yes
• Taken time off work due to injury No Yes
• Been nominated to light duties due to injury No Yes
If yes to any of the above, please provide details:
2. List any medications you take on a regular basis
3. Do you have diabetes? No Yes
a) If yes, please indicate if it is insulin dependent diabetes mellitus (IDDM) or non-insulin dependent diabetes mellitus (NIDDM). IDDM NIDDM
b) If IDDM, for how many years have you had IDDM? ___________years
4. Have you had a stroke? No Yes 5. Has your doctor ever said you have heart trouble? No Yes 6. Do you take asthma medication? No Yes 7. Is there any other physical reason that prevents you from participating
in a pre-employment physical activity program (e.g. cancer, osteoporosis, severe arthritis, mental illness, thyroid, kidney, or liver disease)?
No Yes
8. Do you have Raynaud’s phenomenon, thyroid disease, or any vascular disorders such as venous insufficiency or lower extremity arterial disease?
No Yes
Stage 2 – Signs and Symptoms
9. Do you often have pains in your heart, chest, or surrounding areas, especially during exercise?
No Yes
10. Do you often feel faint or have spells of severe dizziness during exercise?
No Yes
Appendices 101
11. Do you experience unusual fatigue or shortness of breath at rest or with mild exertion?
No Yes
12. Have you had an attack of shortness of breath that came on after you stopped exercising?
No Yes
13. Have you been awakened at night by an attack of shortness of breath? No Yes
14. Do you experience swelling or accumulation of fluid in or around your ankles?
No Yes
15. Do you often get the feeling that your heart is beating faster, racing, or skipping beats, either at rest or during exercise?
No Yes
16. Do you regularly get pains in your calves and lower legs during exercise that are not due to soreness or stiffness?
No Yes
17. Has your doctor ever told you that you have a heart murmur? No Yes Stage 3 - Cardiac Risk Factors
18. Do you smoke cigarettes on a daily basis, or have you quit smoking within the past two years?
No Yes
If yes, how many cigarettes per day do you smoke (or did you smoke in the past two years)? ___________per day
19. Has your doctor ever told you that you have high blood pressure? No Yes
20. Has your father, mother, brother, or sister had a heart attack or suffered from a cardiovascular disease before the age of 55?
No Yes
If yes,
a) Was the relative male or female? ___________
b) At what age did he or she suffer the stroke or heart attack? ___________
c) Did this person die suddenly as a result of the stroke or heart attack? ___________ 21. Do you know your:
a) Blood pressure? ___________mmHg
b) Cholesterol level? ___________mmol/L or mg/dL Stage 4 - Current Exercise
22. What are your current activity patterns?
a) Frequency: ___________exercise sessions per week
b) Intensity: Sedentary Moderate Vigorous
c) History: <3 months 3–12 months >12 months
d) Duration: ___________minutes per session 23. What types of exercises do you do?
102 Appendices
Appendix C Informed Consent
PARTICIPANT INFORMATION FOR QUT RESEARCH PROJECT
Interchangableability of contact and non-contact skin temperature devices
QUT Ethics Approval Number 1300000404 RESEARCH TEAM
Principal Researcher: Aaron Bach – Masters in Applied Science Student Associate Researcher: Ian Stewart – Associate Professor Associate Researcher: Joseph Costello – Postdoctoral Research Fellow Queensland University of Technology (QUT) DESCRIPTION
This project is being undertaken as part of a Masters study for Aaron Bach. The measurement of skin temperature has a wide range of applications that consist of – but are not limited to – exercise performance, the detection of overuse injuries, shock, heat strain, assessing burn and trauma injury, monitoring safe working practices and evaluating cryotherapy treatments. The primary methods of measuring skin temperature are derived from contact and non-contact devices. Each of these measures of skin temperature utilise different principles of thermal heat transfer. Contact methods are based upon thermal conduction between the skin and the measurement device. Popular contact measures include thermistors, thermocouples and iButtons with each device varying in specifications and performance. Non-contact measures – thermal imaging cameras and infrared thermometers – detect infrared energy being emitted from the skin. We have identified a gap in the literature where by few authors have considered the potential difference between contact and non-contact technologies. This oversight is particularly disconcerting in the management of workplace safety, exercise performance and clinical diagnosis – where considerable changes in the technology, particularly thermal imaging cameras, have occurred. The purpose of this research is to identify the current ‘gold standard’ in skin temperature measurement during resting and exercise conditions. To do this 4 devices will be used; 2 contact – thermistor and iButton – and 2 non-contact – infrared camera and infrared thermometer.
a) Wired Thermistor; b) Wireless iButton; c) Infrared Thermometer; d) Infrared Camera.
PARTICIPATION
Testing will involve measuring your skin temperature with the 4 different (non-invasive) devices during rest, exercise and recovery.
• On arrival your skin fold measurements will then be taken to determine your body fat percentage.
• Following that you will have four regions of interest cleaned and marked – 1. Back of your neck, 2. RIGHT shoulder blade, 3. Back of your LEFT hand & 4. The WHOLE front of your RIGHT shin.
a) b) c) d)
Appendices 103
• All testing will take place in a temperature controlled room (where you will be able to watch movies while you are seated). 1. After a 20 minute seated adjustment period, you will sit passively for a further 30
minutes for the resting measurement period (room temperature = 24 °C). 2. You will then enter an environmental chamber (room temperature = 38 °C) where you
will cycle for 30 minutes at 60 rpm (with a 2.0 kg weighted basket). 3. You will then return to the 24 °C room and remain seated for a further 45 minute
recording period. Skin temperature will be taken with the two independent contact measures (wireless iButton and wired Thermocouple) adhered to each site with sports tape. Two other non-invasive, non-contact devices will be used to measure skin temperature at the same sites. The first is an infrared thermometer, which a research member will hold above the surface of your skin to take an instant skin temperature measurement. The second is an infrared camera, this camera will be used to take still images of four skin sites to analyse skin temperature. The infrared camera will be set up on a tripod in front of you when measurements are required and taking the photo is exactly the same as a traditional camera. It should be known that skin temperature measurements taken with the infrared camera are done so by taking non-identifiable still images of your skin. Heart rate, core body temperature and rating of perceived exertion will also be monitored throughout any exercise undertaken in this study. Your participation in this project is entirely voluntary. • To ensure accurate measurements from the camera we ask you avoid prolonged sun exposure
five days prior to the testing day (to prevent sunburn). • All sites will be need to be free of hair, so if appropriate, please shave the areas shown (Figure
1) no closer than 36hours before testing. This prevents inflammation or damage to the skin surface from shaving influencing skin temperature values.
• If you are testing in the morning eat a normal breakfast with 500mL of water before arriving to the lab. If you are testing in the afternoon then eat a normal lunch with 500mL of water before arriving to the lab.
• On the day of testing please keep the sites (Figure 1) clean of make-up, topical agents, creams etc; not to engage in vigorous exercise, ingest caffeine or alcohol. Also do not have a hot shower within two hours of testing (e.g. no later than 8am, if testing at 10am).
• Clothing needs to be unencumbering and conducive to exercise (i.e. runners, socks, shorts and a t-shirt). There are showers, change rooms and toilets for you after if you wish to bring a change of clothes.
• Bring a water bottle, and food if you wish (there is a kitchen next door to reheat any food). • Testing will take approximately 3-4hours. Your decision to participate or not participate will in no way impact upon your current or future relationship with QUT (for example your grades). If you do agree to participate you can withdraw from the project at any time without comment or penalty. Any identifiable information already obtained from you will be destroyed.
Figure 1. Areas that need shaving no closer than 36 hours before testing.
e.g. if you have testing on a Wednesday morning, shave no later than Monday night before bed.
104 Appendices
EXPECTED BENEFITS
It is expected that this project will not benefit you directly. However, by participating in this research you will be helping to determine the difference between contact and non-contact forms of skin temperature measures. This could have valuable applications in sporting, clinical and occupational settings; through greater understanding of physiological relationships between the skin during exercise, the diagnosis of thermal skin conditions (e.g. pressure ulcers) and workplace safety standards (e.g. mining).
To compensate you for your contribution, should you choose to participate, the research team will provide you with a report of your individual results of body characteristics (ie. body fat percentage and Body Mass Index (BMI)).
RISKS
There are minimal risks associated with your participation in this project. All exercise testing has the potential for complications such as fatigue, muscle soreness, irregular heartbeat, chest pain and rarely heart attack. This risk will be minimised through health screening, prior to the commencement of testing. To minimize these risks further you will have a trained exercise scientist supervising all testing. In addition, you will have your heart rate and rate of perceived exertion monitored continuously during any exercise. The exercise will be discontinued if any abnormal heart rate or rhythm is detected with immediate medical attention sought. All exercise within this study will take place on an exercise bike which is a safer testing modality than a treadmill. Exercise also has the potential to lead to heat illness, although would not be expected in this study with moderate intensity exercise. Nevertheless, you will be informed of the signs and symptoms of heat illness, and encouraged to stop exercising if you experience them. A trained exercise scientist will also stop the test if signs and symptoms of heat illness are present. Core body temperature will be monitored continuously throughout the exercise tests, and is a gold standard indicator of heat illness. If core temperature reaches 39 degrees Celsius the test will be terminated. This cut off limit is in-line with the recommendations of the International Organisation for Standardisation (ISO 9886: 2004). Should the test be terminated due to symptoms of heat illness or reaching the core body temperature limit, you will be moved from the bike and onto a mat. Cooling procedures including rest, sips of cool water, fanning, and removal of excess clothing will be initiated. Should the test be terminated due to any complications immediate medical attention will be sought. This will be done by calling for an ambulance and alerting QUT security. Attachment of contact devices to the skin requires adhesive tape. This could potentially be an allergen to yourself and will be asked of in pre-testing screening. Low allogeneic tape will be used to help minimise any reactions if you are not aware of a prior adhesive allergy. If an allergy occurs we will document the incident and notify a doctor that of the reaction and send you to get medical treatment and evaluation. The risks present in the current investigation will be monitored and controlled. This research has the potential to lead to improved field tests for skin temperature assessment and as a result increase safety in sporting, occupational, research and clinical settings. PRIVACY AND CONFIDENTIALITY
Any data collected (including images) as part of this project will be stored securely as per QUT’s Management of research data policy i.e., All information provided to or collected by the research team will be treated confidentially. Individuals will not be identified in any papers reporting the findings of the present investigation. Please note that non-identifiable data collected in this project may be used as comparative data in future projects.
CONSENT TO PARTICIPATE
We would like to ask you to sign a written consent form (enclosed) to confirm your agreement to participate. Images taken with the infrared camera will be used for data collection in the study and
Appendices 105
have the potential to be used for journal publications, conference presentations and teaching materials. It is not expected that you will be identifiable due to the close proximity the images will be taken and the output of the image displays your skin in various colours that represent a given temperature. Should the images be identifiable, measures will be taken to ensure anonymity (i.e. covering identifiable facial features).
QUESTIONS / FURTHER INFORMATION ABOUT THE PROJECT
If have any questions or require further information please contact one of the research team members below.
Aaron Bach Ian Stewart Joseph Costello School of Exercise & Nutrition Sciences
Institute of Health & Biomedical Innovation
School of Exercise & Nutrition Sciences
07 3138 8296 07 3138 6118 07 3138 4168 [email protected] [email protected] [email protected]
CONCERNS / COMPLAINTS REGARDING THE CONDUCT OF THE PROJECT
QUT is committed to research integrity and the ethical conduct of research projects. However, if you do have any concerns or complaints about the ethical conduct of the project you may contact the QUT Research Ethics Unit on 07 3138 5123 or email [email protected]. The QUT Research Ethics Unit is not connected with the research project and can facilitate a resolution to your concern in an impartial manner.
Thank you for helping with this research project. Please keep this sheet for your information.
Appendices 106
Appendix D Complete graphed data for mean skin temperature and all individual sites
Figure D1. Mean skin temperature (MTSK) of all tested devices during rest (4 devices), exercise (3 devices) and recovery (4 devices). TM: Thermistor; IB: iButton®; IT: Infrared Thermometer; IC: Infrared Camera.
Appendices 107
Figure
D2. Neck skin
temperature of all tested devices during rest (4 devices), exercise (3 devices) and recovery (4 devices). TM: Thermistor; IB: iButton®; IT: Infrared Thermometer; IC: Infrared Camera
Appendices 108
Figure D3. Scapula skin temperature of all tested devices during rest (4 devices), exercise (3 devices) and recovery (4 devices). TM: Thermistor; IB: iButton®; IT: Infrared Thermometer; IC: Infrared Camera.
Appendices 109
Figure D4. Hand skin temperature of all tested devices during rest (4 devices), exercise (3 devices) and recovery (4 devices). TM: Thermistor; IB: iButton®; IT: Infrared Thermometer; IC: Infrared Camera.
Appendices 110
Figure D5. Shin skin temperature of all tested devices during rest (4 devices), exercise (3 devices) and recovery (4 devices). TM: Thermistor; IB: iButton®; IT: Infrared Thermometer; IC: Infrared Camera.
Appendices 111
Appendix E Complete ANOVA outputs for all sites and conditions
Thermoneutral (Neck) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F3, 87 =56.188 F10, 290 = 0.821 F30, 870 = 1.809 P<0.001 P = 0.442 P = 0.047 1 - β = 1.00 1 - β = 0.182 1 - β = 0.882
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.212 0.06 -0.378 -0.047
TM : IT -0.479 <0.001 -0.73 -0.227
TM : IC -0.931 <0.001 -1.184 -0.678
IB : IT -0.266 0.004 -0.463 -0.069
IB : IC -0.719 <0.001 -0.926 -0.511
IT : IC -0.452 <0.001 -0.65 -0.255
Thermoneutral (Scap) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F3, 87 = 57.664 F10, 290 = 1.923 F30, 870 = 1.319 P<0.001 P = 0.140 P = 0.231 1 - β = 1.00 1 - β = 0.449 1 - β = 0.618
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.136 0.089 -0.285 0.013
TM : IT -0.335 <0.001 -0.539 -0.132
TM : IC -0.901 <0.001 -1.164 -0.639
IB : IT -0.199 0.016 -0.371 -0.027
IB : IC -0.765 <0.001 -1.008 -0.523
IT : IC -0.566 <0.001 -0.77 -0.362
Thermoneutral (Hand) Normally Distributed (Sphericity Assumed) Within Subjects:
Device Time Device * Time F3, 87 =32.747 F10, 290 = 58.156 F30, 870 = 1.220 P<0.001 P<0.001 P = 0.194 1 - β = 1.00 1 - β = 1.00 1 - β = 0.951
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.064 1.000 -0.326 -0.197
TM : IT -0.249 0.016 -0.464 -0.035
TM : IC -0.867 <0.001 -1.181 -0.554
IB : IT -0.185 0.324 -0.446 -0.076
IB : IC -0.803 <0.001 -1.169 -0.437
IT : IC -0.618 <0.001 -0.831 -0.405
112 Appendices
Thermoneutral (Shin) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F3, 87 =46.130 F10, 290 = 24.342 F30, 870 = 1.462 P<0.001 P<0.001 P = 0.196 1 - β = 1.00 1 - β = 1.00 1 - β = 0.550
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB 0.338 0.002 -0.378 -0.047
TM : IT -0.252 0.002 -0.73 -0.227
TM : IC -0.661 <0.001 -1.184 -0.678
IB : IT -0.590 <0.001 -0.463 -0.069
IB : IC -0.999 <0.001 -0.926 -0.511
IT : IC -0.410 <0.001 -0.65 -0.255 Thermoneutral (MTSK) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F3, 87 = 103.773 F10, 290 = 5.687 F30, 870 = 2.734 P<0.001 P = 0.008 P = 0.004 1 - β = 1.00 1 - β = 0.802 1 - β = 0.960
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.013 1.000 -0.113 0.087
TM : IT -0.339 <0.001 -0.447 -0.231
TM : IC -0.834 <0.001 -1.031 -0.638
IB : IT -0.326 <0.001 -0.433 -0.219
IB : IC -0.821 <0.001 -1.020 -0.623
IT : IC -0.495 <0.001 -0.670 -0.320
Exercise (Neck) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F2, 58 = 58.750 F10, 290 = 71.581 F20, 580 = 77.915 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM:IB -0.196 0.001 -0.314 -0.078
TM:IRT 0.429 <0.001 0.247 0.661
IB:IRT 0.625 <0.001 0.482 0.768
Appendices 113
Exercise (Scap) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F2, 58 = 72.949 F10, 290 = 130.067 F20, 580 = 68.607 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.0
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM:IB -0.270 <0.001 -0.385 -0.155
TM:IRT 0.450 <0.001 0.263 0.637
IB:IRT 0.720 <0.001 0.572 0.868 Exercise (Hand) Normally Distributed (Sphericity Assumed) Within Subjects:
Device Time Device * Time F2, 58 = 20.744 F10, 290 = 56.628 F20, 580 = 35.504 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM:IB -0.188 0.061 -0.382 0.007
TM:IRT 0.298 0.001 0.115 0.482
IB:IRT 0.486 <0.001 0.284 0.688 Exercise (Shin) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F2, 58 = 44.407 F10, 290 = 118.014 F20, 580 = 119.411 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM:IB -0.331 0.001 -0.539 -0.123
TM:IRT 0.592 <0.001 0.360 0.824
IB:IRT 0.923 <0.001 0.617 1.229
114 Appendices
Exercise (MTSK) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F2, 58 = 154.077 F10, 290 = 189.469 F20, 580 = 155.539 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM:IB -0.253 <0.001 -0.335 -0.172
TM:IRT 0.460 <0.001 0.339 0.581
IB:IRT 0.713 <0.001 0.606 0.821
Recovery (Neck) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F3, 87 =102.988 F10, 290 = 80.111 F30, 870 = 97.880 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.360 0.047 -0.717 -0.003
TM : IT -1.423 <0.001 -1.834 -1.013
TM : IC -2.232 <0.001 -2.720 -1.744
IB : IT -1.064 <0.001 -1.466 -0.662
IB : IC -1.873 <0.001 -2.334 -1.411
IT : IC -0.809 <0.001 -1.053 -0.565 Recovery (Scap) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F3, 87 =100.922 F10, 290 = 83.283 F30, 870 = 59.846 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.508 <0.001 -0.723 -0.293
TM : IT -1.250 <0.001 -1.655 -0.845
TM : IC -2.047 <0.001 -2.469 -1.625
IB : IT -0.743 <0.001 -1.143 -0.343
IB : IC -1.539 <0.001 -1.950 -1.128
IT : IC -0.796 <0.001 -1.002 -0.590
Appendices 115
Recovery (Hand) Not Normally Distributed (Greenhouse-Geisser) Within Subjects:
Device Time Device * Time F3, 87 = 75.515 F10, 290 = 23.089 F30, 870 = 38.563 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.524 0.001 -0.872 -0.177
TM : IT -1.007 <0.001 -1.316 -0.699
TM : IC -1.992 <0.001 -2.446 -1.538
IB : IT -0.483 0.006 -0.856 -0.110
IB : IC -1.467 <0.001 -1.949 -0.985
IT : IC -0.984 <0.001 -1.333 -0.636 Recovery (Shin) Normally Distributed (Sphericity Assumed) Within Subjects:
Device Time Device * Time F3, 87 = 52.567 F10, 290 = 82.102 F30, 870 = 59.082 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.143 1.000 -0.443 0.157
TM : IT -0.476 <0.001 -0.729 -0.224
TM : IC -1.288 <0.001 -1.672 -0.904
IB : IT -0.333 0.011 -0.608 -0.059
IB : IC -1.145 <0.001 -1.556 -0.735
IT : IC -0.812 <0.001 -1.064 -0.560 Recovery (MTSK) Normally Distributed (Sphericity Assumed) Within Subjects:
Device Time Device * Time F3, 87 = 178.865 F10, 290 = 122.189 F30, 870 = 125.082 P<0.001 P<0.001 P<0.001 1 - β = 1.00 1 - β = 1.00 1 - β = 1.00
Pairwise Comparisons: Mean Diff (Devices)
95% CI
Devices Mean Diff Sig. Lower Upper
TM : IB -0.367 <0.001 -0.530 -0.203
TM : IT -1.041 <0.001 -1.263 -0.819
TM : IC -1.880 <0.001 -2.194 -1.567
IB : IT -0.674 <0.001 -0.912 -0.436
IB : IC -1.514 <0.001 -1.828 -1.199
IT : IC -0.840 <0.001 -1.034 -0.645
116 Appendices
Appendix F Complete post-hoc paired sample T-test comparisons between all devices
RESTING: TIME POINT 1 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM6 - IB6 -.03833 .17473 .03190 -.10358 .02691 -1.202 29 .239 Pair 2 TM6 - IT6 -.40500 .24387 .04452 -.49606 -.31394 -9.096 29 .000 Pair 3 TM6 - IC6 -.82500 .41931 .07655 -.98157 -.66843 -10.777 29 .000 Pair 4 IB6 - IT6 -.36667 .25444 .04645 -.46168 -.27166 -7.893 29 .000 Pair 5 IB6 - IC6 -.78667 .42367 .07735 -.94487 -.62846 -10.170 29 .000 Pair 6 IT6 - IC6 -.42000 .34780 .06350 -.54987 -.29013 -6.614 29 .000
RESTING: TIME POINT 6 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM6 - IB6 -.00433 .20056 .03662 -.07922 .07056 -.118 29 .907 Pair 2 TM6 - IT6 -.35200 .21640 .03951 -.43281 -.27119 -8.909 29 .000 Pair 3 TM6 - IC6 -.85200 .40954 .07477 -1.00493 -.69907 -11.395 29 .000 Pair 4 IB6 - IT6 -.34767 .22758 .04155 -.43265 -.26269 -8.368 29 .000 Pair 5 IB6 - IC6 -.84767 .40463 .07387 -.99876 -.69658 -11.474 29 .000 Pair 6 IT6 - IC6 -.50000 .35912 .06557 -.63410 -.36590 -7.626 29 .000
RESTING: TIME POINT 11 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM11 - IB11 -.01633 .20934 .03822 -.09450 .06184 -.427 29 .672 Pair 2 TM11 - IT11 -.30633 .22590 .04124 -.39069 -.22198 -7.427 29 .000 Pair 3 TM11 - IC11 -.82967 .41824 .07636 -.98584 -.67350 -10.865 29 .000 Pair 4 IB11 - IT11 -.29000 .22273 .04066 -.37317 -.20683 -7.132 29 .000 Pair 5 IB11 - IC11 -.81333 .40276 .07353 -.96373 -.66294 -11.061 29 .000 Pair 6 IT11 - IC11 -.52333 .37295 .06809 -.66260 -.38407 -7.686 29 .000
EXERCISE: TIME POINT 1 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM1 - IB1 .56033 .25957 .04739 .46341 .65726 11.824 29 .000 Pair 2 TM1 - IT1 -.84333 .36812 .06721 -.98079 -.70587 -12.548 29 .000 Pair 3 IB1 - IT1 -1.40367 .42796 .07813 -1.56347 -1.24386 -17.965 29 .000
Appendices 117
EXERCISE: TIME POINT 3 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM3 - IB3 -.02567 .18207 .03324 -.09365 .04232 -.772 29 .446 Pair 2 TM3 - IT3 .31767 .47157 .08610 .14158 .49375 3.690 29 .001 Pair 3 IB3 - IT3 .34333 .53107 .09696 .14503 .54164 3.541 29 .001
EXERCISE: TIME POINT 5 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM5 - IB5 -.26900 .19691 .03595 -.34253 -.19547 -7.482 29 .000 Pair 2 TM5 - IT5 .88333 .30942 .05649 .76779 .99887 15.636 29 .000 Pair 3 IB5 - IT5 1.15233 .28459 .05196 1.04607 1.25860 22.178 29 .000
EXERCISE: TIME POINT 7 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM7 - IB7 -.46967 .23187 .04233 -.55625 -.38309 -11.095 29 .000 Pair 2 TM7 - IT7 .80867 .34804 .06354 .67871 .93863 12.726 29 .000 Pair 3 IB7 - IT7 1.27833 .25890 .04727 1.18166 1.37501 27.044 29 .000
EXERCISE: TIME POINT 9 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM9 - IB9 -.56867 .26540 .04846 -.66777 -.46956 -11.736 29 .000 Pair 2 TM9 - IT9 .66400 .37243 .06800 .52493 .80307 9.765 29 .000 Pair 3 IB9 - IT9 1.23267 .28173 .05144 1.12747 1.33787 23.965 29 .000
EXERCISE: TIME POINT 11 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper
Pair 1 TM11 - IB11 -.56633 .28089 .05128 -.67122 -.46145 -11.043 29 .000 Pair 2 TM11 - IT11 .46000 .40085 .07319 .31032 .60968 6.285 29 .000 Pair 3 IB11 - IT11 1.02633 .43068 .07863 .86551 1.18715 13.052 29 .000
118 Appendices
RECOVERY: TIME POINT 1 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error Mean
95% Confidence Interval of the Difference
Lower Upper
Pair 1 TM1 - IB1 -1.04833 .37850 .06910 -1.18967 -.90700 -15.170 29 .000 Pair 2 TM1 - IT1 .91500 .32953 .06016 .79195 1.03805 15.208 29 .000 Pair 3 TM1 - IC1 -.14167 .42099 .07686 -.29887 .01553 -1.843 29 .076 Pair 4 IB1 - IT1 1.96333 .53700 .09804 1.76281 2.16385 20.025 29 .000 Pair 5 IB1 - IC1 .90667 .58539 .10688 .68808 1.12525 8.483 29 .000 Pair 6 IT1 - IC1 -1.05667 .35689 .06516 -1.18993 -.92340 -16.217 29 .000
RECOVERY: TIME POINT 3 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM3 - IB3 -.78633 .41649 .07604 -.94185 -.63081 -10.341 29 .000 Pair 2 TM3 - IT3 -.68133 .70501 .12872 -.94459 -.41808 -5.293 29 .000 Pair 3 TM3 - IC3 -1.67133 .71143 .12989 -1.93699 -1.40568 -12.867 29 .000 Pair 4 IB3 - IT3 .10500 .67656 .12352 -.14763 .35763 .850 29 .402 Pair 5 IB3 - IC3 -.88500 .69064 .12609 -1.14289 -.62711 -7.019 29 .000 Pair 6 IT3 - IC3 -.99000 .42778 .07810 -1.14974 -.83026 -12.676 29 .000
RECOVERY: TIME POINT 5 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM5 - IB5 -.57200 .40761 .07442 -.72420 -.41980 -7.686 29 .000 Pair 2 TM5 - IT5 -1.41200 .63361 .11568 -1.64859 -1.17541 -12.206 29 .000 Pair 3 TM5 - IC5 -2.36200 .79389 .14494 -2.65844 -2.06556 -16.296 29 .000 Pair 4 IB5 - IT5 -.84000 .64571 .11789 -1.08111 -.59889 -7.125 29 .000 Pair 5 IB5 - IC5 -1.79000 .77939 .14230 -2.08103 -1.49897 -12.579 29 .000 Pair 6 IT5 - IC5 -.95000 .39018 .07124 -1.09570 -.80430 -13.336 29 .000
RECOVERY: TIME POINT 7 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM7 - IB7 -.39067 .37203 .06792 -.52959 -.25175 -5.752 29 .000 Pair 2 TM7 - IT7 -1.57267 .64407 .11759 -1.81317 -1.33217 -13.374 29 .000 Pair 3 TM7 - IC7 -2.43267 .81105 .14808 -2.73552 -2.12981 -16.428 29 .000 Pair 4 IB7 - IT7 -1.18200 .58924 .10758 -1.40203 -.96197 -10.987 29 .000 Pair 5 IB7 - IC7 -2.04200 .73798 .13474 -2.31757 -1.76643 -15.156 29 .000 Pair 6 IT7 - IC7 -.86000 .39966 .07297 -1.00923 -.71077 -11.786 29 .000
Appendices 119
RECOVERY: TIME POINT 9 Paired Samples Test
Paired Differences t
df
Sig. (2-tailed)
Mean
SD
Std. Error
Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM9 - IB9 -.22967 .33020 .06029 -.35296 -.10637 -3.810 29 .001 Pair 2 TM9 - IT9 -1.56567 .61919 .11305 -1.79687 -1.33446 -13.850 29 .000 Pair 3 TM9 - IC9 -2.33233 .78754 .14378 -2.62641 -2.03826 -16.221 29 .000 Pair 4 IB9 - IT9 -1.33600 .57647 .10525 -1.55126 -1.12074 -12.694 29 .000 Pair 5 IB9 - IC9 -2.10267 .73868 .13486 -2.37850 -1.82684 -15.591 29 .000 Pair 6 IT9 - IC9 -.76667 .40797 .07448 -.91900 -.61433 -10.293 29 .000
RECOVERY: TIME POINT 11 Paired Samples Test
Paired Differences
t df Sig. (2-tailed) Mean
Std. Deviatio
n
Std. Error Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM11 - IB11 -.10433 .33236 .06068 -.22844 .01977 -1.719 29 .096 Pair 2 TM11 - IT11 -1.39200 .59198 .10808 -1.61305 -1.17095 -12.879 29 .000 Pair 3 TM11 - IC11 -2.09867 .77252 .14104 -2.38713 -1.81020 -14.880 29 .000 Pair 4 IB11 - IT11 -1.28767 .56843 .10378 -1.49992 -1.07541 -12.408 29 .000 Pair 5 IB11 - IC11 -1.99433 .71118 .12984 -2.25989 -1.72877 -15.359 29 .000 Pair 6 IT11 - IC11 -.70667 .39994 .07302 -.85601 -.55733 -9.678 29 .000
RECOVERY: TIME POINT 13 Paired Samples Test
Paired Differences t df Sig. (2-tailed) Mean Std.
Deviation
Std. Error Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM13 - IB13 .01067 .34506 .06300 -.11818 .13952 .169 29 .867 Pair 2 TM13 - IT13 -1.12033 .50539 .09227 -1.30905 -.93162 -12.142 29 .000 Pair 3 TM13 - IC13 -1.81700 .66392 .12121 -2.06491 -1.56909 -14.990 29 .000 Pair 4 IB13 - IT13 -1.13100 .51541 .09410 -1.32346 -.93854 -12.019 29 .000 Pair 5 IB13 - IC13 -1.82767 .64326 .11744 -2.06786 -1.58747 -15.562 29 .000 Pair 6 IT13 - IC13 -.69667 .43667 .07972 -.85972 -.53361 -8.738 29 .000
RECOVERY: TIME POINT 15 Paired Samples Test
Paired Differences t df Sig. (2-tailed) Mean Std.
Deviation
Std. Error Mean
95% Confidence Interval of the Difference
Lower Upper Pair 1 TM15 - IB15 .08933 .34195 .06243 -.03835 .21702 1.431 29 .163 Pair 2 TM15 - IT15 -.86467 .39044 .07128 -1.01046 -.71887 -12.130 29 .000 Pair 3 TM15 - IC15 -1.54467 .59057 .10782 -1.76519 -1.32414 -14.326 29 .000 Pair 4 IB15 - IT15 -.95400 .46458 .08482 -1.12748 -.78052 -11.247 29 .000 Pair 5 IB15 - IC15 -1.63400 .61274 .11187 -1.86280 -1.40520 -14.606 29 .000 Pair 6 IT15 - IC15 -.68000 .41473 .07572 -.83486 -.52514 -8.981 29 .000
References 121
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