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Body Composition Testing

Stephanie Marz

Dr. Kendall

March 10, 2014

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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.

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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.

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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.

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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

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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.

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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

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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

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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

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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.

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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.

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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):_______________

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APPENDIX B