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1
Body Composition Testing
Stephanie Marz
Dr. Kendall
March 10, 2014
2
INTRODUCTION
In a society that is health-conscious yet still grossly overweight, body composition
measurements can be important for any population. Body composition measurements are used by
a variety of professionals in the health industry and can be used to assess people on both ends of
the spectrum, from the fittest athlete all the way to a morbidly obese person. However, some
measurements are more accurate than others, and not all types of measurements will work on
every population. Body composition is the relative percentage of fat and non-fat tissue in the
body, and there are many ways it can be measured, including circumference, skinfolds,
bioelectrical impedance analysis (BIA), BOD POD, dual-energy x-ray absorptiometry (DEXA),
and hydrostatic weighing (Kendall, 2014).
Circumference is the most basic way to measure the body, and it is virtually the only
method that will provide accurate results on an obese individual. A waist-to-hip ratio can be
obtained and used to determine if individuals are at a greater risk of developing cardiovascular
disease (Kendall, 2014).
Skinfolds and BIA, both two-compartment (2C) models, are the most commonly used
field-tests to measure body composition in a non-clinical setting. Both methods are inexpensive,
portable, and easy to use. However, neither method will yield accurate results on obese
individuals. For BIA testing, individuals must be properly hydrated prior to testing. BIA is based
on the water conductivity in the body, and lean body mass is composed of a much greater
percentage of water than fat mass. Therefore, the less resistance an electrical current has passing
through the body, the more water they have and the leaner they are (Kendall, 2014).
Some techniques, including hydrostatic weighing, BOD POD, and DEXA, estimate body
density to help determine body composition. Body densities are calculated based on the
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assumption that fat has a density of 0.9 kg/L and fat-free tissue has a density of 1.1 kg/L. The
biggest problem with this is the assumed fat-free (muscle, organs, and bone) tissue density,
which can vary drastically based on ethnicity (Kendall, 2014). While fat and muscle density
remains fairly consistent, bone densities can considerably vary from 1, 180 to 1,330 kg m-3,
depending on various factors (Barlett et al., 2010). However, not all body composition
measurements rely on a formula using body density.
The BOD POD and DEXA are lab-based tests that are more complex and expensive ways
of assessing body composition. While hydrostatic weighing is the gold standard measurement for
2C models, it is expensive and usually not as feasible as using the BOD POD. While hydrostatic
weighing uses water displacement to calculate body density, the BOD POD measures air
displacement, and then uses body volume and body weight to estimate body density. Unlike the
BOD POD, DEXA, a three-compartment (3C) model, uses x-ray to assess the body. X-ray has an
easier time passing through less dense tissue and body density is figured from the x-ray pattern.
Body composition using 2C models is usually more feasible and cheaper than using 3C
models. The problem with 2C models is the lack of separation in fat-free mass, between muscles
and other components, such as organs and bones, all of which have different densities. 3C
models use fat mass, fat-free lean mass, and either total body water (from BIA) or bone mineral
density (from DEXA). 3C models separate the type of fat free mass, allowing for more accurate
densities. A 3C model using total body water (TBW) is likely to produce a more varied result
than using bone density. Hydration status of an individual is going to play a bigger role in
accurate results (Kendall, 2014), since muscle mass is about 75% water and fat is about 10%
water (Niedziocha, 2013).
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All methods for determining body composition have their strengths and weaknesses, and
while methods like the BOD POD or DEXA may be ideal, it isn’t always feasible or affordable
to use, especially in a field-based setting. It is important to identify the accuracy of field
methods, such as skinfolds and BIA, in comparison with more complex body composition
methods to determine how accurate field-method results are. Duz et al. (2009) performed a study
in a population of young males and females using DEXA as a reference point. It was compared
to skinfolds, BIA and ultrasound, and was found that these three could not be used
interchangeably in their population of normoactive individuals because they all produced
significantly lower body fat results than the DEXA. In another body composition comparison
study by Dixon and Andreacci (2009), it was found that BIA produced similar body fat percent
results as BOD POD in a population of young adults. In a study by Andreoli et al. (2004) in
professional water polo players, they found that a 3C model using total body water and a 2C
model (underwater weighting) were acceptable, while skinfolds and BIA overestimated body fat
and a 3C model using bone density (from DEXA) underestimated percent body fat. There is a
large variation in results comparing body composition methods.
Therefore, the purpose of this study is to compare the results of four different methods
(skinfolds, BIA, BOD POD, and DEXA) utilized to measure body composition to determine
discrepancies between the different methods, and to determine if field tests can yield similar
results to lab tests.
5
METHODS
Subject Description
Thirteen non-obese graduate students (24.1 ± 3.1 years) participated in this study. Of the
thirteen, five were male and eight were female. All participants were familiar with exercise and
have an active lifestyle.
Calibration Procedures
The BOD POD and DEXA were the two pieces of body composition equipment that
needed to be calibrated prior to use.
BOD POD
• Turn on BOD POD system and let it warm up for 30 minutes.
• Calibrate the BOD POD.
o Analyze the hardware by performing the Quality Control (QC).
o Calibrate and check the scale.
o Perform the QC Auto run and follow the instructions on the screen.
o Perform a QC Volume test.
• Make sure participant has had no food, water, or exercise at least two hours prior
to testing, is relaxed and at a normal body temperature, has removed all jewelry
and accessories, and is wearing minimal clothing.
• Enter basic participant information into the computer program.
• Participant will step on the calibrated scale to measure mass.
• Participant will enter the BOD POD to have body volume measured.
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DEXA
• Turn on DEXA software.
• Click on “Daily QC Setup”.
• Place calibration block on the DEXA surface as indicated by the laser.
• Hit “Continue” and then “OK”.
Testing Protocol
Numerous measurements for body composition were taken and recorded on an individual
data sheet (Appendix A) using circumference, skinfolds, BIA, BOD POD, and DEXA.
Circumference was measured using a flexible tape measure at the waist and hip for all
individuals. Waist measurements were taken at the smallest part of the torso and hip
measurements were taken around the largest part of the buttocks. Results were recorded in
centimeters and were used to determine the waist-to-hip ratio.
Skinfolds measurements were taken using Lange skinfold calipers (Model EQ0014921)
at seven sites on the body and recorded in millimeters. The sites included the chest, triceps,
subsapularis, midaxillary, abdomen, suprailiac, and thigh. Measurements were taken twice from
each site if both readings were within two mm of each other. If not, a third measurement was
taken and the average was used. To obtain a valid reading, it was crucial that each pinch was
deep enough to get all of the fat, but not so deep that muscle was pinched as well. A vertical
pinch was typically made for each site, except at the chest, subscapularis and suprailiac, where a
diagonal pinch was made. After deciding where the proper location was to use the calipers,
fingers were used to pinch the fat about an inch above that location so they did not get in the
way. These measurements were then plugged in to the Brozek equation to estimate percent body
fat.
7
Bioelectrical impedance analysis (BIA) was conducted using a Bodystat Multiscan 4000
Bioimpedance Analyzer (Bodystat Limited, Isle of Man, Brisish Isles). Individuals laid down for
approximately ten minutes with no body parts touching another body part. To prep the
individual, if necessary, the areas where electrodes are placed were shaved. Then, those areas
were cleaned with an alcohol wipe. Following prep, two Bodystat® disposable electrodes were
placed on their right hand, one on the top of the hand below the knuckles and one between the
bony prominences on the wrist, and two more electrodes were placed on their right foot, one on
the top of the foot below the toes and one between the bony prominences on the ankle. Individual
information was entered into the machine, then the analysis started and body composition results
were given.
Prior to using the BOD POD® (COSMED USA, Inc., Chicago, IL), it was calibrated.
Individuals wore wear minimum clothing before entering the BOD POD. Males wore
compression shorts and females wore wear spandex shorts and a sports bra. A BOD POD cap
was worn to cover hair on males and females, but females tied their hair up in a bun to fit the cap
over it. Individuals then stepped inside the BOD POD, sat down, and remained still while it is
measuring body composition. Two 50-second measurements were taken and then results were
displayed. The Brozek equation was used to determine body fat percentage.
Prior to using the DEXA machine, it was calibrated. Following calibration, individuals
laid on the DEXA table, making sure all body parts were within the white lines. Their legs were
strapped together to ensure they stay together. They remained completely still for the duration of
the scan, which was typically less than ten minutes. Following the scan, results were displayed.
8
Description of Physiological Variables
Body composition is the relative percentage of fat tissue in the body and the non-fat
tissue. There are several variables that were measured during the body composition lab. Fat mass
(FM), fat-free mass (FFM), lean body mass (LBM), and percentage of body fat all help make up
overall body composition. Fat mass is simply the amount of adipose in the body. Fat-free mass
and lean body mass are often used interchangeably, but they are not the same. Fat-free mass
encompasses muscle, bone and organs, whereas lean body mass just refers to the muscle mass.
Percentage of body fat is simply the fat mass divided by overall body mass. Circumference is the
distance measured around a body part. Total body water is the total amount of water in the body,
which is made up of intracellular water and extracellular water. Bone mineral content is the
amount of fat-free mass that comes from the human skeleton. Body volume is measured by the
amount of air (or water) displaced by the body. Lower volumes will lead to lower air
displacement. Body density can be calculated by dividing body mass by body volume. The closer
a density is to 1.1 kg/L instead of 0.9kg/L, the leaner the individual will be (Kendall, 2014).
Data Analysis
The mean ± standard deviation was found for basic subject characteristics, including age,
height and weight, and was separated by gender. All body composition mean ± standard
deviations were reported and split by gender. Mean ± standard deviation was reported for
circumference measurements, as well as percentage of body fat found from skinfolds, BIA, BOD
POD, and DEXA. Mean ± standard deviation was reported for a 3-compartment model: total
body water (percentage of fat, fat mass, and fat free mass) (Siri, 1961) and a 3-compartment
model: bone mineral content (percentage of fat, fat mass, and fat free mass) (Lohman, 1986). A
9
one-way repeated-measures ANOVA was performed to compare overall results for the
percentage of body fat determined by the skinfolds, BIA, BOD POD, and DEXA. For these same
four variables, two more ANOVAs were performed, one for males and one for females. An
additional repeated measures ANOVA was performed to compare the percentage of fat between
the BOD POD, the 3-comparment model: water, and the 3-compartment model: mineral. For
these same three variables, two more ANOVAs were performed, one for males and one for
females. For each ANOVA, a Pairwise Comparison was used to determine statistical significance
between modes. In addition, a regression was performed to estimate body fat percentage using
the 3C TBW model as the main criteria, while also including skinfold sum, age, height, weight,
and BMC. Statistical significance was set at p<0.05. Statistics were determined using SPSS 21.
10
RESULTS
All thirteen students completed the body composition testing and recorded their results
(Appendix B). Table 1 below shows gender differences in basic characteristics including age,
height, and weight. Males were significantly taller and heavier than females.
TABLE 1. Subject characteristics by gender: means ±SD for age, height, and weight. *Indicates statistical significance (p<0.05). Physical Description Female Male P-Value
Age (years) 24.87 ±3.83 22.8 ± 0.84 0.18
Height (cm) 166. 37 ± 12.28 177.54 ± 5.62 0.049*
Weight (kg) 60.31 ± 11.67 82.08 ± 14.59 0.012*
Table 2 indicates gender differences in body fat percentage when looking at each mode of
measurement. There was no significant difference in body fat percentage between genders when
the DEXA and BOD POD were used. However, females yielded significantly higher percentages
of body fat than males when measured via BIA and skinfolds.
TABLE 2. Body fat percentage- Split by gender: units in %BF for DEXA, BOD POD, BIA, and skinfolds. Circumference data reported in centimeters. *Indicates statistical significance (p<0.05).
Measurement Mode Female Male P-Value
DEXA 26.16 ± 7.25 19.36 ± 7.72 0.076
BOD POD 18.28 ± 9.19 13.94 ± 4.71 0.144
BIA 24.65 ± 5.87 14.94 ± 3.33 0.0009*
Skinfolds 22.79 ± 6.01 14.59 ± 5.1 0.014*
Hip Circumference (cm) 95.09 ± 8.67 99.9 ± 9.07 0.185
Waist Circumference (cm) 69.49 ± 6.83 83.4 ± 7.74 0.006*
Table 3 shows values for using two different 3C models to calculate body fat percentage
and shows statistical differences between gender and model. The 3C model using total body
11
water (3C TBW) was the only 3C mode to show a significant difference in body fat percentage
between genders. When looking at each gender separately, there was a significant difference
between 3C model body fat percentages.
TABLE 3. Shows differences in body fat percentage between gender and mode of 3-compartment measurement. *Indicates statistical significance (p<0.05).
%BF: 3C BMC %BF: 3C TBW P-Value Between 3C Models
Males 10.36 ± 4.84 17.13 ± 3.95 0.0005*
Females 17.89 ± 11.82 24.27 ± 8.34 0.0039* P-Value Between
Gender 0.07 0.032* -
Figure 1 shows mode differences in body fat percentage results. The BOD POD was the
only mode that was significantly different from each of the three other modes. There was no
difference between BIA versus DEXA or skinfolds.
23.55 16.61 19.64 20.91 0
5
10
15
20
25
30
35
DEXA BODPOD SKINFOLD BIA
% B
ody
Fat
Mode of Body Fat Assessment
Differences in Mean Body Fat Percentage between Modes
*
FIGURE 1: Displays mean ± SD of %BF between modes and includes data from both genders. *DEXA: significantly higher than skinfolds (p=0.004) and BOD POD. **BOD POD: significantly lower than DEXA (p<0.001), skinfolds (p=0.008), and BIA (p=0.013)
**
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Figure 2 shows how body fat percentage differs within each gender depending on the
mode that is used to determine body fat. The results from the BOD POD were significantly lower
in females and the DEXA results were significantly higher in males.
Figure 3 compares body fat percentage between the BOD POD, 3C model using TBW
and 3C model using BMC. The 3C TBW model yielded significantly higher results.
26.16
19.36 18.27 13.94
24.65
14.94
22.79
14.56
0
5
10
15
20
25
30
Female Male
% B
ody
Fat
Gender
Mode %BF Differences Within Each Gender
DEXA
BODPOD
BIA
SKINFOLD
**
FIGURE 2: Shows the difference in mean body fat percentage between modes within each gender. *In females, BOD POD produced significantly lower results than DEXA (p=0.008), BIA (p=0.013), and skinfold measurements (p=0.007). **In males, DEXA produced significantly higher results than BOD POD (p=0.025) and skinfolds (p=0.27).
*
16.61 21.52 14.99 0 5
10 15 20 25 30 35
BODPOD 3C TBW 3C BMC
% B
ody
Fat
Mode for Determining Body Fat
Comparing %BF between BOD POD, 3C TBW and 3C BMC
FIGURE 3: Shows differences in body fat percentage between BOD POD results, 3-compartment (3C) model formula using total body water (3C TBW), and 3C model formula using bone mineral content (3C BMC). **3C TBW yielded significantly higher reuslts than the BOD POD (p<0.001) and the 3C model using BMC (p<0.001).
**
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Based on the results found in this study, a regression equation was developed to predict
body fat percentage using the 3C TBW formula as a constant. The equation is as follows:
%BF= 0.176(sum of skinfolds mm) + 13.171(BMC) + 1.671(age yrs) + 0.007(height cm) -
0.688(weight kg) – 29.455.
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DISCUSSION
In overall results, the BOD POD underestimated body fat in comparison to the other three
modes, while DEXA overestimated in comparison with BOD POD and skinfolds. In females, the
most interesting result was that the BOD POD significantly underestimated body fat when
compared to the three other modes, while there were no significant differences between DEXA,
BIA, and skinfolds. In males, the DEXA significantly overestimated body fat, while there were
no significant differences between the BOD POD, BIA, and skinfolds. Sardinha et al. (1998) also
found that DEXA produced significantly higher results than BOD POD in males. It was
interesting that when separated by gender, only one lab method was significantly different from
the other methods, while the other was not. In addition, it was a different lab method for each
gender, and one was higher while the other was lower. It is unclear why this would be the case.
Results in the present study showed that BIA was never significantly different when
compared with DEXA or skinfolds, and when compared to the BOD POD, BIA estimated a
significantly higher body fat percentage overall and in females. This is different from a study
performed by Dixon and Andreacci (2009), where it was found that BIA significantly
underestimated body fat percentage in men and women when compared with the BOD POD.
In this study, the BOD POD and 3C BMC model produced significantly lower results
than other measures of determining body fat. The 3C BMC model uses the body density value
obtained from BOD POD, so if body density is overestimated by the BOD POD, it will also
skew the results for the 3C formula using BMC. While appearing relatively accurate for most
individuals, in the case of short females who were more lean, the BOD POD produced
unrealistically low results, and the 3C: BMC model produced body fat results so low that it
would be virtually impossible to survive. In addition to the 3C BMC model using body density
15
from the BOD POD, it also uses BMC from DEXA. Smaller people will have smaller amounts of
BMC, adding another variable that could have yielded falsely low results. Andreoli et al. (2004)
also found that a 3C model using DEXA underestimated body fat percentage. However, a study
performed by Vescovi et al. (2001) found that in lean, but not average or overweight subjects,
body density was measured much lower using the BOD POD in comparison with hydrostatic
weighing, therefore resulting in an overestimation of body fat percentage. However, this study
does not mention any differences based on height.
The estimated body fat percentages in this present study using the 3C TBW formula was
significantly higher than using the 3C BMC formula and the BOD POD, but was not
significantly different from DEXA or BIA. This was different from Andreoli et al. (2004), which
found that BIA was significantly higher than a 3C TBW formula. However, this could be
because Andreoli et al. used hydrostatic weighing to determine body density, unlike the present
study, which used the BOD POD.
One of the biggest methodological problems with this study was the unequal and small
sample size. Many studies used over 40 participants (Dixon and Andreacci, 2009 ; Duz et al.,
2009 ; King et al., 2009 ; Sardinha et al., 1998), and this study only had 13 participants, with an
unequal number of males and females. This makes it difficult to obtain meaningful results
between differences for genders and mode. In addition, the BOD POD testing was done on a
different day than the other tests. This could have allowed for participant discrepancies in
weight, hydration, state of fasting, and how rested they were. Another problem could have come
from skinfold measurements. The same person did not take skinfolds for every participant, and
some people who took measurements were experienced and others were not, which could result
in a big under or overestimation of body fat percentage.
16
CONCLUSION
All field and lab methods of determining body fat percentage are not interchangeable.
Skinfolds are likely not a good replacement for lab methods, as they yielded significantly higher
results than the BOD POD and significantly lower results than the DEXA. However, in a field
setting, using BIA in place of DEXA to estimate body fat percentage is likely to yield similar
results. Also, if field-based methods are the only option, BIA and skinfolds yield comparable
results. When comparing lab-based methods, results from the BOD POD and DEXA were
significantly different and could not be used interchangeably. In addition, based on the findings
of this study, it is not recommended that the BOD POD or 3C BMC model be used to determine
relatively accurate estimated body fat percentages on short, leaner females.
17
REFERENCES
Andreoli, A., Melchiorri, G., Volpe, S., Sardella, F., Iacopino, L., & DeLorenzo, A. (2004). Multicompartment model to assess body composition in professional water polo players. Journal of Sports Medicine and Physical Fitness,44, 38-43.
Barlett, R., Gratton, C., & Rolf, C. (2010). Encyclopedia of international sports studies. (p. 164).
Abingdon, Oxon and New York, NT: Routledge. Retrieved from http://books.google.com/books?id=t6CaJM_BXR0C&pg=PA165&lpg=PA165&dq=1.1 density fat free mass formula ethnicity&source=bl&ots=NAesdeRqTE&sig=3Cq7HZVhQLcS-bklZfGMsU7TYIE&hl=en&sa=X&ei=Ltr8UqSqK6uyygHJ2oCYCA&ved=0CDcQ6AEwAw
Dixon, C., & J, A. (2009). Comparison of body composition measurements from contact-
electrode bioimpedance analyzers with air-displacement plethysmography in young adults. International Journal of Body Composition Research, 7(3), 109-115.
Duz, S., Kocak, M., & Korkusuz, F. (2009). Evaluation of body composition using three
different methods compared to dual-energy x-ray absorptiometry. European Journal of Sport Science, 9(3), 181-190. doi: 10.1080/17461390902763425
Kendall, K. (2014). Body composition. Lecture notes, Georgia Southern University. Niedziocha, L. (2013, Aug 16). Does muscle tissue have less water than fat tissue?. Retrieved
from http://www.livestrong.com/article/550931-does-muscle-tissue-have-less-water-than-fat-tissue/
Sardinha, L., Lohman, T., Teixeira, P., Guedes, D., & Going, S. (1998). Comparison of air
displacement plethysmography with dual-energy x-ray absorptiometry and 3 field methods for estimating body composition in middle-age men. American Journal of Clinical Nutrition, 68, 786-793.
Vescovi, J., Zimmerman, S., Miller, W., Hildebrandt, L., Hammer, R., & Fernhall, B. (2001).
Evaluation of the bod pod for estimating percentage body fat in a heterogeneous group of adult humans. European Journal of Applied Physiology, 85, 326-332.
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APPENDIX A
Name: Sex: __________ Age: Height: (cm) Weight: (kgs) BOD POD Volume: %BF: Lung Volume: Fat Weight (kg): Body Volume: Lean Weight (kg): Density: DEXA %BF: ________ Fat Mass (kg):__________ BMC (kg): ________ Fat Free Mass (kg): ________ BIA TBW (L): Fat Free Mass (kg): Fat Mass (kg): %BF: Skinfolds Chest(mm)_____________ Triceps(mm)______________ Subscapularis(mm)_________ Midaxillary(mm)___________ Abdomen(mm)__________ Suprailiac(mm)____________ Thigh(mm)_____________ Total Skinfold Sum (mm)____________ Circumference Waist(cm):_____________________ Hip(cm):_______________
19
APPENDIX B