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7/26/2019 Welk PA in Children for Measurement Class.doc
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Measurement Issues in the Assessment of Physical
Activity in ChildrenKeywords: self-report, activity monitors, observation, validity, activity patterns
Gregory J. Welk, Charles B. Corbin and Darren Dale
The health benefits of physical activity for adults have been well established (U.S. Department of
Health and Human Services, !!"#. Similar lin$s with children are not as well established since
it ta$es time for unhealthy behaviors to influence chronic disease. %evertheless, there has been
tremendous interest in assessin& and promotin& physical activity amon& children. 'uch of thisinterest stems from the hi&hly publicied increases in the prevalence of pediatric obesity
()ortma$er, Diet, Sobol, * +ehler, ! Troiano, /le&al, 0ucmars$i, 1ampell, * 2ohnson,
!!3 Troiano * /le&al, !!#. Studies have documented the important role that physical activityplays in wei&ht control (4ippe * Hess, !!# and si&nificant trac$in& coefficients have been
observed for obesity (+hita$er, +ri&ht, * Diet, !!#, coronary ris$ factors ('ahoney, 5auer,
5ee, * 1lar$e, !!# and physical activity6inactivity (7ate, 8aranows$i, Dowda, * Trost, !!"7ate et al., !!!# amon& youth. To advance wor$ in these (and other# areas, and further the
promotion of physical activity in children, continued efforts are needed to improve our ability to
assess this comple9 behavior.
There are a number of different techniues that have been used to assess physical activity in avariety of populations (self-report, activity monitors, pedometers, heart rate monitors, doubly
labeled water, and indirect calorimetry# and others that have been developed specifically for
children (direct observation#. ;ach of the measures has specific advanta&es and disadvanta&esthat must be considered when selectin& an instrument. < number of e9cellent reviews of physical
activity assessments have described the relative merits of the different approaches for adults
(
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review some of the more common physical assessment tools to determine the usefulness of each
in studyin& childrenAs physical activity.
Table . 1haracteristics That Differentiate 1hildren /rom
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bout of hi&h intensity activity lon&er than minutes was recorded. The median duration
between hi&h intensity activities was seconds, but ran&ed between ? s and > min. 3 s.
7eriods of rest were clearly lon& in proportion to periods of activity, but !3G of the IrestAintervals were less than = min. and 3 s. This indicates that children do not remain inactive for
e9tended periods of time. 1ollectively, these findin&s clearly document the hi&hly transitory
nature of childrenAs physical activity. The authors su&&est that short, intermittent bouts ofvi&orous physical activity (with freuent rest periods of lon&er duration# are typical of children
and, in fact, may be necessary for normal &rowth and development (8ailey et al., !!3#.
Table >. < Summary of %
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in physical activity. The implications of these various characteristics of children for each of the
more common assessment techniues will be discussed later in this paper.
Uniqe %cti&ity Gidelines "or Children
2ust as the uniue characteristics of children should be considered when ma$in& decisions about
the method of physical assessment so too should the uniue e9pectations for children in activitybe considered. The need to assess physical activity in any population is based on the desire to
determine the current activity status of that population and to determine if that population ismeetin& activity criteria that are appropriate for optimal health and development. /or years, the
activity &uidelines for children were assumed to be similar to those recommended for adults
(#. The recent % hours# G of children
with H4 M ?! for
> consecutiveminutes
Girls: 12%
active Boys: 23%active
Girls: 53%
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G of children
with H4 M ?! for ?,
3-minute bouts
Total number
of minutes with H4M ?! (wee$day#
Boys: 70%
Girls: 32
minutes Boys: 45minutes
hours# G of children
with H4 M ?! for >
consecutive minutes
G of children
with H4 M ?! for ?,
3-minute bouts
Total number of
minutes with H4
M?! (wee$day#
Girls: 34%
active Boys: 39%
Girls: 85%
Boys: 90%
Girls: 59
minutes Boys: 68minutes
hours6day over ?
days#
G of children
with H4 M ?! for >
consecutive minutes
G of children
with H4 M ?! for ?,
3-minute bouts
G of children
with H4 M 3! for ?,3-minute bouts
Girls: 37%
Boys: 39.5%
Girls: 88%
Boys: 92%
Girls: 70% Boys
79%
)illiam
(!>#
&irls and >> boys
a&es "-
1ontinuous heart rate
monitorin& (> hours# Total number of
minutes with H4 M"
Total number of
minutes with H4 M
=
Girls: 9 minutes
Boys: 21 minutes
Girls: 30
minutes Boys: 56minutes
2an (!!># " &irls and boys
a&es "-
1ontinuous heart rate
monitorin& (-
hours#
G of children
with H4 M "G of a&e
predicted ma9 for >minutes
Total number of
minutes with H4 M"G of a&e predictedma9 N 33 bpm
Total: 7% active
Total: 15
minutes
Direct bser&ation +tdies
Baranos!i"1987#
14 $irls an 10&oys a$es 8'12
(irect o&servationon to ays "12)ours#1
% o* c)ilren
active *or 20consecutive
8'13% o*
c)ilren
58'63% o*
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minutes
% o* c)ilren
active *or 14minutes it) only 1sto+ or &rea!
Total num&er o*minutes o* activity(reported for thosewho were "active")
c)ilren
61'71 total
minutes o* activity
,lea+"1992#
27 $irls an 29&oys
(irect o&servation2 % o* c)ilren
active *or 20consecutiveminutes
% o* c)ilren
active *or 10consecutiveminutes
Total minutes
o* activity
14% o* c)ilren
active
46% o* c)ilren
active
88.5 minutes
+el"-)eport Instrments
-rai$"1996#
49 $irls a$es 8'11 ,el*'re+ort o*+revious year
vera$e
minutes +er ay inmoerate activity /4 Ts
96.7 minutes
Gortma!eret al."1999#
336 5t)$raec)ilren
To activityassessments 1. 24)r recall 2. 16'itemsurvey
um&er o*
minutes o*moerate +)ysicalactivity / 6 Tscom+ute it) tomeasures
inutes +er
ay *or treatmentan control $rou+s1. 72'82 minutes2. 89'99 minutes
curray"1998#
45 c)ilren "25$irls an 20 &oys#in $raes 6'8
-om+uterieactivity recall
um&er o*
minutes o* +)ysicalactivity "nos+ecication o*intensity#
Girls: 85
minutes Boys: 67minutes
yers"1996#
995 &oys an $irlsa$es 9'15
,el*'e+ort o*+revious ay",-#
um&er o*
minutes o* +)ysicalactivity
Total: 168
minutes
oss "1985# ational sam+le o*
5t)
an 6t)
$rae
arent re+ort o*
c)ils activity3
% o* c)ilren
+er*ormin$ re$ularactivity
um&er o*
minutes o* +)ysicalactivity
Girls: 49%
Boys: 56% Total:102'120 minutes
,imons'orton
2410 3r$raec)ilren
ctivity ntervieit) a lo$
um&er o*
minutes o*
Girls: 83
minutes Boys: 97
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"1997# moerate tovi$orous activity aay
minutes
ey *or a&&reviations: ; )eart rate< ; +)ysical activity= ,- ; ,el*'ministere )ysicalctivity ecall
1ctivity ene as continuous slo or *ast trun! movements2ctivity ene as &ein$ commensurate it) a )eart rate o* 140 &+m
3ctivity ene as >e?ercise involvin$ lar$e muscle $rou+s in ynamic movement *or +erios o* 20minutes or lon$er 3 or more times a ee!.>
Characteriing %cti&ity 'e&els in Children
@f the assessment of physical activity patterns of children is the &oal, the standard used to define
Ebein& activeF becomes hi&hly relevant. /ailure to use appropriate standards can lead tosi&nificant misinterpretations of both individual and &roup assessments of physical activity.
@nterpretations of studies on activity levels in children also can vary widely dependin& on what
type of assessment is used. Some e9amples illustratin& the importance of these issues for
characteriin& activity levels in children are provided below.7rior to the development of specific physical activity standards for children, many studies were
conducted to evaluate the habitual activity levels of children. To provide obOective information
about activity patterns, a number of studies used heart rate monitors (. @ntensity of 7 isolated days of measurement.
The intensity of physical activity is often used to cate&orie physical activity but is notcommonly used as an outcome measure. Several studies have reported mean heart rates or mean
activity counts durin& the day or portion of the day (2an et al., !!> 2an, !!=#. +hile this
may be useful for statistical comparisons, the values themselves are difficult to interpret. 8ecausethe maOority of a childAs day is spent in restin& or li&ht activities, mean values would be low and
would not provide meanin&ful information about their true activity level. @f mean levels were
reported for a &roup, the lar&e intra-individual variability in activity patterns in children would
ma$e interpretations of the data even more difficult.The duration of activity is &enerally reported in minutes or percenta&e of time spent bein& active.
#.
Lbtainin& ener&y e9penditure estimates from physical activity reuires information about themetabolic costs of the activities that are performed. /or indirect calorimetry and doubly labeled
water techniues, these measures are made directly accordin& to established metabolic
calculations. /or observation and self-report measures, estimates are typically made usin&multiples of restin& metabolic rate (';TS#. 8ecause the ';T values for various activities are
not well established for children (
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@t is apparent from Table = that a number of different approaches can be used to obtain a similar
outcome measure. The ease and accuracy of assessin& these different components varies amon&
each of the instruments. The advanta&es, disadvanta&es, and specific measurement issues forassessin& childrenAs activity behaviors will be described below.
Self-Report Instruments
Self-report instruments provide a convenient way to assess activity patterns on lar&e populations.
+hile they have been commonly used for a variety of research purposes, there is widespreadconcern about the accuracy of self-report data from children. 'ost validation studies with
children have reported only moderate correlations between various self-report forms and other
obOective criteria (Sallis, !!#. The lac$ of stron& correspondence and the described tendencyfor overestimation have led to the consensus that children can not provide accurate self-report
information about their activity patterns. ;fforts have been made to describe the co&nitive and
methodolo&ical issues pla&uin& self-report instruments (8aranows$i et al., !=#, but little is$nown about the specific co&nitive s$ills reuired for children (or adults# to accurately complete
self-reports (8aranows$i, !3 8aranows$i, ! Du4ant *
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have recently been published to facilitate their use by both researchers and teachers (+el$ *
+ood, >#.
Heart Rate Monitors
Heart rate monitors provide an obOective indicator of the physiolo&ical effect of physical activity.They have been found to provide a valid measure of heart rate in children (Du4ant et al., !!?
Treiber et al., !!#, and heart rate has been shown to be linearly related to PL>and ener&y
e9penditure durin& physical activity. However, the numerous other factors that influence heartrate under restin& conditions contribute considerable error when heart rate monitors are used for
e9tended periods of monitorin&. @n a recent study (+el$, 1orbin, * 0ampert, !!#, we found
that heart rate indicators were hi&hly correlated with a direct observation measure under activeconditions in physical education (r .!#, but wea$ly correlated under inactive conditions in the
classroom (r .=!#. +hile this type of error would bias measures of mean heart rate, they would
not affect estimates of total minutes of activity (e.&., minutes M = bpm#. Still, there are a
number of difficulties inherent in usin& heart rate monitors for field-based research (4iddoch *
8oreham, !!3#. 7roblems with "-cycle interference and lost data from si&nal interruptionsma$e data collection and data processin& challen&in&. Delayed heart rate responses and the
influence of other factors can add considerable error to heart rate recordin&s. Discomfort fromwearin& a transmitter device can also reduce participant compliance.
/i&ure . Hypothetical dia&ram illustratin& the potential variability in activity patterns within a minute for a child.
8ecause childrenJs activity is hi&hly sporadic and intermittent, short bouts of activity would be avera&ed with rest
brea$s to represent the activity level for the minute. @f activity cutpoints based on steady-state activity are used, theminute may be scored as inactive despite the presence of some vi&orous activity.
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< promisin& application of heart rate monitorin& techniues is for estimations of ener&y
e9penditure and for studies on obesity and wei&ht control (5ivin&stone, !!#. Usin&
individualied H4: PL>re&ression euations and techniues that control for errors caused byvariability in restin& heart rate, a number of studies have demonstrated stron& predictions for
ener&y e9penditure in children (5ivin&stone et al., !!> Spady, ! Treuth,
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direct observation techniues usin& momentary time samplin& procedures may provide the best
criterion measure since they can address chan&es in activity levels within a minute.
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wee$ periods, and does not interfere with normal activity patterns. The limitations are the cost
and the difficulty in obtainin& the stable isotopes of water. @t is also not useful for e9aminin&
patterns of activity or for partitionin& ener&y e9penditure associated with physical activity.@nterested readers are referred to more detailed descriptions of these techniues and their
applicability for research on children ()oran, !!3 Hill, 2ohnson, 'elby, * 7eters, !!3
+esterterp * )oran, !!#.
+mmary
This paper reviewed the nature of childrenAs physical activity patterns and how the uniue nature
of children can impact the assessment of physical activity. To accurately assess childrenAs activity
patterns, an instrument must be sensitive enou&h to detect, code, or record sporadic andintermittent activity. 1are also must be used to select criterion measures that reflect appropriate
physical activity &uidelines for children.
< number of different measurement approaches have been described for assessin& childrenAs
activity, but no specific method can be identified as the best option for all studies. Selection of anappropriate instrument depends on the specific research uestion bein& addressed as well as the
relative importance of accuracy and practicality (8aranows$i * Simons-'orton, !!#. /or
e9ample, accurate measures of ener&y e9penditure usin& doubly-labeled water, indirect
calorimetry, or heart rate calibration euations may be needed for certain clinical studies, but thecost and inconvenience would ma$e them impractical for field-based assessments on lar&er
samples.
The Eaccuracy-practicalityF trade-off presents a more challen&in& predicament with children thanfor adults. @n adults, a number of self-report instruments have been found useful for lar&e
epidemiolo&ical studies or interventions where less precision is needed. 8ecause of
developmental differences, especially in ability to thin$ abstractly and perform detailed recall()oin& et al., !!! Sallis, !!#, children are less li$ely to ma$e accurate self-report assessmentthan adults. Thou&h self-report methods are still li$ely to be a principal source of information for
many studies, other approaches (or the use of combined measures# may be needed to better
characterie childrenAs activity levels.
+hile obOective instruments (e.&., direct observation or activity monitorin reuire more timeand resources than self-report, there are options available to simplify data collection. Lne
approach may be to focus assessments on $ey times or places that allow children to be active.
The time after school, for e9ample, appears to be a critical period that defines their propensity forphysical activity (Ha&er, !!!#. 'onitorin& of entire &roups for discrete periods of time (e.&.,
recess or physical education# may also be useful to understand variability in activity patterns
since children would all be e9posed to the same stimulus or opportunity to be active.
7ro9y measures may also be useful in studyin& activity in children. /or e9ample, several studies(8aranows$i, Thompson, Du4ant, 8aranows$i, * 7uhl, !!? Sallis et al., !!?# have
demonstrated that time spent outside is stron&ly predictive of activity in children. @nvolvement in
community sports pro&rams may also be a useful pro9y measure as sports pro&rams have been
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found to account for appro9imately 33-"3G of childrenAs moderate to vi&orous activity
(0atmary$ * 'alina, !!!#.
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>-=>?.
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