Validity of 2 Skinfold Calipers in Estimating Percent Body Fat of College-Aged Men and Women : The Journal of Strength & Conditioning Research

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Original Research

Validity of 2 Skinfold Calipers in Estimating Percent Body Fat of College-Aged Men and Women

Beam, Jason R1; Szymanski, David J2

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Journal of Strength and Conditioning Research 24(12):p 3448-3456, December 2010. | DOI: 10.1519/JSC.0b013e3181bde1fe
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Abstract

Introduction

Knowledge of percent body fat (%BF) is useful in health and fitness assessments and in predicting athletic performance. However, body composition assessment methods vary in their cost, accuracy, strengths, and limitations. A clinician or researcher must consider the practical aspects of their assessment needs and weigh this against the limitations of the methods (27). There is a need for cost-effective techniques that accurately predict %BF and require little skill to administer.

Underwater weighing and dual-energy X-ray absorptiometry (DXA) are 2 reference methods used to assess body composition, whereas bioelectrical impedance analysis and skinfold analysis are 2 field methods. Although underwater weighing and DXA are more precise in measuring %BF than bioelectrical impedance analysis and skinfold analysis, they are more time consuming, inconvenient, and costly (27). Because underwater weighing and DXA are more accurate in measuring %BF than bioelectrical impedance analysis and skinfold analysis, past research has utilized these techniques as reference methods to validate arm-to-arm bioelectrical impedance analysis (Omron, Shelton, Connecticut, USA) (10,17,20), leg-to-leg bioelectrical impedance analysis (Tanita, Arlington Heights, Illinois, USA) (5,6,22,23) and 3-site skinfold equations (SUM3) (1-3,7,8,12-14,16,24,26) in males and females.

The Accu-Measure Fitness 3000 Personal Body Fat Tester (Accu-Measure, AccuFitness, Greenwood Village, Colorado, USA) and the FatTrack Gold Digital Body Fat Caliper (FatTrack, AccuFitness) are 2 inexpensive commercially available skinfold calipers. The Accu-Measure has been validated using underwater weighing as a reference method (9). The results of this study indicated that the Accu-Measure was a valid method of assessing %BF in college-aged Caucasian men and women with lean to average %BF when compared to underwater weighing. The authors of the study recommended that future studies be conducted to confirm their findings with similar samples of men and women along with athletes and groups differing in age and ethnicity. No studies to date have validated the Accu-Measure using DXA as a reference method. Furthermore, no studies to date have validated the FatTrack against a reference method. Therefore, the primary purpose of this study was to validate the Accu-Measure and FatTrack using DXA as a reference method in a sample of lean to overweight college-aged men and women from a kinesiology department. A secondary purpose of this study was to compare the validity of the Accu-Measure and FatTrack to the validity of Omron, Tanita, and SUM3 using DXA as a reference method.

Methods

Experimental Approach to the Problem

An individual's health, fitness level, and athletic performance are affected by %BF. The ability to use reliable, accurate, and inexpensive equipment to assess %BF is very important. If one can find tools on the market that can accomplish this, then more expensive, time-consuming methods that require advanced training or equipment may not be needed. The Accu-Measure has been validated in 1 other study (9) using underwater weighing as the reference method. The present study is the first to evaluate the validity of the Accu-Measure when using DXA as the reference method. The FatTrack has not been validated against a reference method in any study prior to the present one. The other field methods in the present study (Tanita, Omron, and SUM3) were compared to DXA so that we could evaluate the group and individual predictive accuracy of these methods to the Accu-Measure and FatTrack.

DXA is an advanced method of body composition that simultaneously measures bone, lean body mass, and fat mass (3 components) without having to make assumptions about their densities (1). It is safe and requires minimal subject cooperation (1). For these reasons, DXA is being used as a reference method against which other techniques can be compared. However, based on previous research evaluating %BF values from DXA compared to other reference methods (3,7,11,21,28), it was hypothesized that all of the %BF values for the methods used in the present study would be lower than DXA %BF values because all other methods used in this study are based off of underwater weighing.

Subjects

Twenty-five college-aged men and 25 college-aged women from a kinesiology department who ranged in fitness levels volunteered to participate in this study. The purpose of the study and a description of the testing protocol were explained to each subject. Subjects were informed of the experimental risks and signed an informed consent that was approved by the University Institutional Review Board prior to the commencement of this study. Basic descriptive data, such as age, height, weight, body mass index, waist girth, hip girth, and waist-to-hip ratio can be seen in Table 1.

T1-33
Table 1:
Descriptive characteristics for the men and women.

Procedures

All participants were tested for %BF using 6 different methods in a randomized order to break up any systematic relationship between the incidental aspects of the procedure and the 6 different methods (18). All body composition determinations were performed on the same day in the morning following a 12-hour fast (ad libitum water intake was allowed). The subjects were instructed to avoid exercise for at least 12 hours prior to testing, to not consume alcohol the night before or on the day of testing, and to not take a bath immediately before testing.

Dual-Energy X-Ray Absorptiometry

Participants met either at the Green Clinic or Northern Louisiana Medical Center to have their %BF assessed by a Lunar Prodigy DXA (software version, enCORE 2006, Madison, Wisconsin, U.S.A.). Each organization assisted with 25 participants. Before each test, each subject's height, body mass, gender, and race were entered into the computer program. Subjects were asked to wear shorts and a t-shirt and to remove any objects containing metal. Then, they were positioned supine on the DXA table with their forearms pronated and hands flat and asked to remain motionless while their body was scanned. Each whole-body scan lasted approximately 8 to 10 minutes, depending on the height of the subject. Total body mode was selected for each scan, and scanning thickness was determined by the DXA software. All DXA scans were conducted by a certified enCORE software operator. The DXA was calibrated according to the manufacturer's specifications at the beginning of each testing session using a calibration standard provided with the scanner. The total regional %BF measured by the DXA was used as the reference %BF.

Skinfold Analysis

Skinfold thickness was measured on the right side of the body with a calibrated Lange skinfold caliper (Beta Technology Incorporated, Cambridge, Massachusetts, USA) and the FatTrack (AccuFitness) by an investigator who had previously demonstrated a test-retest reliability of r > 0.90. Measurements were taken according to the recommendations of Jackson and Pollock (15) at the chest, abdomen, and thigh for the men and at the triceps, suprailiac, and thigh for the women while subjects were standing. The order in which the participants were measured by each skinfold caliper was randomized, with some getting measured by the Lange first and some by the FatTrack first. The investigator rotated through the measurement sites using a tape measure for proper location once and then repeated the measurements a second time in rotation. If the measurements were not within 1 to 2 mm, the measurements were repeated a third time. The average of the 2 Lange skinfold measurements within 1 to 2 mm for each site were manually averaged and summed together. Body density values were calculated using the SUM3 skinfold equations of Jackson and Pollock for the men (14) and Jackson, Pollock, and Ward for the women (16). The body density values were then converted to %BF using the formula of Siri (25): %BF = [(4.95/body density) × 4.50] × 100. The procedures described by the manufacturer for using the FatTrack were followed. Each skinfold site was pinched by the FatTrack until the caliper beeped. After all 3 skinfold sites were measured, the FatTrack automatically calculated %BF based on the previous SUM3 formulas.

Each subject assessed their own %BF while standing using the Accu-Measure according to the protocol described by the manufacturer (AccuFitness). Following a detailed explanation of the procedure, subjects practiced 10 times measuring the suprailiac skinfold on the right side of their body. Using the left thumb and forefinger, they grasped the skinfold 1 inch above the iliac crest and placed the jaws of the instrument over the midpoint of the skinfold using the right hand. They then pressed with the right thumb until they felt a slight click when the slide member automatically stopped at the appropriate reading. The measurement was recorded to the nearest millimeter and the slide member was returned to the starting position. After the participant consistently measured their suprailiac skinfold within 1 to 2 mm, the procedure was repeated 3 times and the average of the 3 readings were used as the representative value, as recommended by the manufacturer. The subject's gender, age, and skinfold measurements were used to determine %BF using the charts provided by the manufacturer.

Bioelectrical Impedance Analysis

Each subject's %BF was measured while standing on a leg-to-leg Tanita BF-350 Body Composition Analyzer (Tanita) according to the procedures recommended by the manufacturer (Tanita Corporation, Tokyo, Japan). Each subject's %BF was also measured by an arm-to-arm Omron HBF-300BL Body Logic Body Fat Analyzer (Omron) according to the procedures recommended by the manufacturer (Omron Corporation, Kyoto, Japan).

Statistical Analyses

Data for the men (n = 25) and the women (n = 25) were analyzed separately. The statistical package used for all analyses was SPSS for Windows version 10.0 (SPSS, Inc., Chicago, Illinois, USA). Mean differences (bias) in %BF between all of the field methods and DXA for the men and women were analyzed using paired-samples t-tests. A Bonferroni correction was made to the familywise alpha of 0.05 to control for Type I error (18). The new alpha level for the 2 comparisons was 0.05/5 = 0.01.

The slope, intercept, Pearson product moment correlation coefficient (r), and standard error of estimate (SEE) were all computed from regression analyses of each field method. To assess the average deviation of individual scores from the line of identity, total error (TE) was calculated for each field method using the following equation:

where y' = predicted %BF, y = DXA %BF, and N = the sample size. The bias and 95% limits of agreement (95% LOA) were calculated for each field method. The bias and 95% LOA of the Accu-Measure and FatTrack were graphically depicted using Bland-Altman plots (4).

Results

Overall, the FatTrack and Accu-Measure had the poorest group predictive accuracies of all field methods in estimating %BF for the men and women in the present study when compared to DXA %BF. The group predictive accuracies of the FatTrack and Accu-Measure for the men were better than the group predictive accuracies of the women. The mean %BF measured by all field methods except the Tanita %BF for men significantly underestimated the mean %BF measured by the DXA (p ≤ 0.01) (Table 2). The mean %BF of the Accu-Measure and FatTrack for the men and women were lower than the mean %BF of all of the other field methods. The TE of the Accu-Measure for the men (7.9%BF) and women (10.7%BF) was lower than the TE of the FatTrack for the men (9.0%BF) and women (10.9%BF). However, the TE of the Accu-Measure and FatTrack for the men and women was higher than the TE of all the other field methods (Table 3). This means that the Accu-Measure and FatTrack had the greatest deviation from the line of identity when compared to DXA as the reference method (Figures 1 and 2).

T2-33
Table 2:
Percent body fat for the men and women measured by 6 different methods.
T3-33
Table 3:
Group predictive accuracy for the men and women.
F1-33
Figure 1:
Relationships between Accu-Measure %BF and dual energy X-ray absortiometry (DXA) %BF for the (A) men (n = 25) and (B) women (n = 25).
F2-33
Figure 2:
Relationships between FatTrack %BF and dual energy X-ray absortiometry (DXA) %BF for the (A) men (n = 25) and (B) women (n = 25).

The SEE of the Accu-Measure for the men (3.83%BF) and women (3.71%BF) was higher than the SEE of the FatTrack for the men (2.43%BF) and women (2.29%BF). This was because of the lower correlations of the Accu-Measure compared to the FatTrack for the men (r = 0.92 vs. r = 0.97) and women (r = 0.83 vs. r = 0.94). The Accu-Measure had a lower SEE than the Tanita (5.41%BF) and Omron (4.90%BF) but higher SEE than the SUM3 (2.26%BF) for the men. However, the Accu-Measure had a higher SEE than the Tanita (2.82%BF), Omron (3.17%BF), and SUM3 (2.46%BF) for the women. The lower SEE of the FatTrack and Accu-Measure in the women than the men was mostly a result of the lower standard deviation of the DXA %BF in the women than the men. The greater TE of the FatTrack and Accu-Measure in the women than the men was mostly a result of the greater bias between the Accu-Measure %BF vs. DXA %BF and FatTrack %BF vs. DXA %BF in the women than the men.

The bias and 95% LOA of all field methods are presented in Table 4. Bland-Altman plots of the Accu-Measure and FatTrack can be seen in Figure 3 and Figure 4, respectively. Although the FatTrack had the largest bias for the men (8.4%BF) and women (10.6%BF) when compared to the other field methods, it had the narrowest 95% LOA for the women (5.7 to 15.6%BF) and second narrowest 95% LOA for the men (2.0 to 14.8%BF). The Accu-Measure had a lower bias than the FatTrack for the men (6.7 vs. 8.4%BF) and women (10.0 vs. 10.6%BF) but wider 95% LOA for the men (−1.9 to 15.3%BF vs. 2.0 to 14.8%BF) and women (2.5 to 17.6%BF vs. 5.7 to 15.6%BF). The Accu-Measure had the widest LOA when compared to all other field methods for the women. This indicates the Accu-Measure had the lowest individual predictive accuracy of all the field methods for the women in the present study when compared to DXA. However, the Tanita (−8.8 to 12.4%BF) and Omron (−5.5 to 14.1%BF) had wider 95% LOA than the Accu-Measure (−1.9 to 15.3%BF) for the men.

T4-33
Table 4:
Individual predictive accuracy for the men and women.
F3-33
Figure 3:
Bland-Altman plots comparing Accu-Measure %BF to dual energy X-ray absortiometry (DXA) %BF for the (A) men (n = 25) and (B) women (n = 25).
F4-33
Figure 4:
Bland-Altman plots comparing FatTrack %BF to dual energy X-ray absortiometry (DXA) %BF for the (A) men (n = 25) and (B) women (n = 25).

Discussion

The FatTrack and Accu-Measure had poorer predictive accuracies than the BIA and SUM3 field methods for estimating %BF for the men and women in the present study when referenced to DXA. The group predictive accuracies of the FatTrack and Accu-Measure for the men were better than the group predictive accuracies for the women. However, the individual predictive accuracies of the FatTrack and Accu-Measure for the women were better than the individual predictive accuracies for the men. The individual predictive accuracy of the FatTrack was similar to the individual predictive accuracy of the SUM3 for the women; however, the group predictive accuracy was very different.

The findings in the present study for Accu-Measure were not similar to the findings of the only other study that compared Accu-Measure to a reference method %BF (9). Accu-Measure %BF was compared to underwater weighing in 30 Caucasian men ages 23 ± 3 years and 26 Caucasian women ages 21 ± 2 years. On average, the participants in the study by Eckerson et al. (9) were much leaner than the participants in the present study. The SEE for the Accu-Measure in their study for the men (3.5%) and women (3.6%) were very similar to the SEE for men (4.0%) and women (3.8%) in the present study. However, their TE was much lower in the men (3.5%) and women (3.6%) than the TE for men (7.2%) and women (10.2%) in the present study. Although their correlations were much lower than the correlations in the present study, their mean bias between underwater weighing and Accu-Measure was not significantly different. Eckerson et al. (9) noted that the Accu-Measure condensed the distribution when compared to underwater weighing, which may result in errors at the extreme ends of the body composition distribution. Because DXA was used as the reference method in the present study, and DXA has been found to overestimate %BF compared to other reference methods (3,7,11,21,28), the results of the present study should be interpreted carefully.

The plastic Adipometer skinfold caliper is similar to the plastic Accu-Measure skinfold caliper used in the present study. One study compared the reliability and objectivity of the Lange, Harpenden (baty, West Sussex, United Kingdom, Holtain (Crymych, Wales), and Adipometer skinfold calipers on 16 female college basketball athletes (age: 18.1-21.3 year, mean weight: 64.7 kg) (19). The investigators of this study found that the suprailiac skinfold for the Adipometer (13.9 mm) was significantly lower than the suprailiac skinfold for the Lange (19.2 mm). The mean suprailiac skinfold of the Accu-Measure (14.9 mm) was lower than the mean suprailiac skinfold of the Lange (16.5 mm) for the women in the present study. If the mean suprailiac skinfold of the Accu-Measure for the women was 16.5 mm instead of 14.9 mm, the estimated mean %BF of the Accu-Measure would have been 25.5%BF instead of 23.7%BF. An estimated Accu-Measure %BF of 25.5% for the women would still be lower than the estimated SUM3 %BF (28.8%) and DXA %BF (33.8%). Therefore, some of the systematic bias between the Accu-Measure and DXA for the women in the present study could also be a result of the manufacturer charts provided for calculating Accu-Measure %BF. Furthermore, previous research (3,7,11,21,28) has found DXA to overestimate %BF compared to other reference methods, which the Accu-Measure calculated %BF values are based. Overall, the Accu-Measure was not a very accurate method in estimating %BF of the men and women in the present study when compared to DXA and other field methods.

To our knowledge, the present study is the first to compare the FatTrack to DXA in college men and women. In the present study, the FatTrack had the poorest group predictive accuracy out of all the field methods when compared to DXA for the men (TE = 9.0%BF) and women (TE = 10.9%BF). Greater compression of tissue at the various skinfold sites compared to the Lange skinfold caliper could be the major factor that contributed to the large significant underestimation of %BF by the FatTrack in men and women when compared to DXA in the present study. The skinfold thicknesses measured were consistently lower than the skinfold thickness measured by the Lange skinfold caliper. As a result, the FatTrack had lower SUM3 measurements than the Lange skinfold caliper and therefore lower %BF estimations. The FatTrack had good individual predictive accuracy for the men and women when compared to the other field methods. This was possibly a result of the high correlation between the FatTrack and DXA for the men (r = 0.97) and women (r = 0.94). However, the FatTrack had the largest group bias for the men (8.4%BF) and women (10.6%BF) when compared to the other field methods. Overall, the FatTrack was not a very accurate method in estimating %BF of the men and women in the present study when compared to DXA and other field methods.

The Accu-Measure had poor group predictive accuracy and poor individual predictive accuracy for the men and women when compared to DXA in the present study. The FatTrack had the poorest group predictive accuracy for both men and women; however, it had better individual predictive accuracy than the Accu-Measure for the men and women. From the results of this study, we would not recommend using the FatTrack or Accu-Measure for estimating %BF in college-aged men and women with similar body composition as the men and women in the present study. Compared to the DXA in the present study, the SUM3 for men and Tanita for women had the best group predictive accuracy. The Tanita for men and SUM3 for women had the second best group predictive accuracy. However, the SUM3 had better individual predictive accuracy than the Tanita for men and women. Therefore, we recommend that the SUM3 be used to estimate %BF in college-aged men and women with similar body composition as the men and women in the present study. More research is warranted that assesses whether the Accu-Measure and FatTrack are valid and reliable calipers for measuring skinfold thickness when compared to other valid and reliable calipers, such as the Lange. Because other researchers have found DXA to overestimate %BF compared to other reference methods (3,7,11,21,28), and DXA %BF values were significantly higher than all other methods used in the present study except Tanita %BF for the men, investigators may want to reconsider using DXA as a reference method in research until specifications for standardized instrumentation and software are established. Moreover, investigators may want to consider using correction or regression equations found in other studies (1,2,7,13,21) for DXA with college-aged men and women when comparing %BF estimations to other devices whose calculated %BF values are based off of different reference methods, such as underwater weighing.

Practical Applications

The Accu-Measure is a skinfold caliper that retails around $20 and the FatTrack is a digital skinfold caliper that retails around $50. The Accu-Measure can be used to self-assess an individual's %BF using the suprailiac skinfold; however, an individual cannot assess his or her own %BF using the FatTrack. Based on the results of the present study, we would not recommend using the Accu-Measure or FatTrack to estimate %BF in college-aged men and women. The Tanita, Omron, and SUM3 are valid methods for estimating %BF of a group; however, the Tanita and Omron individual predictive accuracy may not be as good as the SUM3 individual predictive accuracy. Therefore, we would recommend using the Lange skinfold caliper and SUM3 equations to estimate %BF in college-aged men and women with similar body composition as the men and women in the present study.

Acknowledgments

We would like to thank the Green Clinic and Northern Louisiana Medical Center of Ruston, Louisiana for providing the DXA scanners and technologists for our study. We would also like to thank Emily Mire for helping with the data collection and AccuFitness, LLC for donating FatTrack Gold Digital Body Fat Calipers and Accu-Measure Fitness 3000 Personal Body Fat Testers for use in our study. The results of the present study do not constitute endorsement of the evaluated products by the authors or the NSCA.

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Keywords:

dual-energy x-ray absorptiometry; body composition; bioelectrical impedance analysis

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