R. Randall Clark

Prediction of percent body fat in adult males using dual energy x-ray absorptiometry, skinfolds, and hydrostatic weighing.

The purpose of this study was to compare the prediction of percent body fat (%FAT) by dual energy x-ray absorptiometry (DXA), skinfolds (SF), and hydrostatic weighing (HW) in adult males. Subjects were 35 adult male Caucasians (mean +/- SD; age: 39.1 +/- 14.0 yr, height: 180.6 +/- 5.3 cm, weight: 81.0 +/- 11.1 kg). %FAT, determined by HW with residual volume determined via O2 dilution, served as the criterion. DXA %FAT was determined by the Norland XR-26 (XR-26) bone densitometer and by the SF equations of Jackson and Pollock (JP) (1978), and Lohman (LOH) (1981). Criterion referenced validation included analyzing mean (+/- SD) %FAT values using a one-way ANOVA for significance, comparison of mean differences (MD), correlations (r), standard error of estimates (SEE), and total errors (TE). Significant differences were found between means of each method. The r (0.91) and SEE (3.0 %FAT) for DXA compare favorably with the established SF methods of JP and LOH for predicting %FAT; however, DXA demonstrated the largest MD (3.9 %FAT) and TE (5.2 %FAT). Regression analysis yields HW = 0.79* DXA + 0.56. The results do not support earlier research that found no significant difference between HW and DXA %FAT in males. The study suggests the density of the fat-free body (DFFB) is not constant, and that the variation in bone mineral content affects the DFFB, which contributes to the differences between DXA and HW %FAT. We recommend further research to identify inconsistencies between manufacturers of DXA equipment in prediction of %FAT in males.

The effect of dehydration on wrestling minimum weight assessment.

UNLABELLED Given that some wrestlers arrive for minimum weight (MW) testing in a dehydrated condition, it is important to understand the effects of dehydration on MW assessment methods. PURPOSE To determine the effect of dehydration on the assessment of MW by three-site skinfolds with the Lohman formula (SF), leg-to-leg bioelectrical impedance analysis (BIA), and multifrequency bioelectrical impedance spectroscopy (BIS) compared with a four-component (4C) criterion. METHODS Twenty-two male collegiate wrestlers (mean +/- SD, age: 19.9 +/- 1.4 yr, height: 174.0 +/- 6.8 cm, body mass: 77.4 +/- 9.1 kg) had their body composition assessed by the 4C criterion, hydrostatic weighing (HW), SF, BIA, and BIS in euhydration (EUH) and dehydration (DEH). Subjects dehydrated 2-5% of body weight through fluid restriction and exercise in a hot environment. RESULTS In EUH, the total error (TE) for HW (1.75 kg) and SF (2.15 kg) were not significantly different, but the TE for HW and SF methods were significantly lower than the TE for both BIS (3.68 kg) and BIA (3.77 kg). In DEH, SF, BIA, and BIS methods had a TE approaching or exceeding 4 kg (8.8 lb). Dehydration increased the TE for SF and BIA through an artificial lowering of body weight and for BIS by an increased error in intracellular water prediction. CONCLUSION Acute thermal dehydration violates assumptions necessary for the accurate and precise prediction of MW by SF, leg-to-leg BIA, and multifrequency BIS.

A comparison of methods to predict minimal weight in high school wrestlers.

The purpose of this study was to compare the accuracy of body fat determinations and subsequent calculation of minimal weight (MW) by dual energy x-ray absorptiometry (DEXA), bioelectrical impedance (BIA), near-infrared photospectometry (NIR), and anthropometry (LOHMAN). Necessitated by mandatory state minimal weight testing, the methods were cross-validated on 95 Wisconsin high school wrestlers (mean +/- SD; age: 15.1 +/- 1.2 yr, height: 170.4 +/- 7.1 cm, weight: 63.4 +/- 9.8 kg). MW, defined as fat-free body/0.93, determined by hydrostatic weighing (HW) and residual volume via O2 dilution, served as the criterion. The validity of the four selected MW predictions were evaluated against HW by examining mean differences (MD), standard deviation differences (SDD), correlations (r), standard error of estimate (SEE), and total errors (TE). Statistically significant differences were shown between the methods and the criterion by t-tests; however, these were clinically small in Lohman (0.6 kg) and BIA (0.9 kg). TE ranged from 2.25 kg (Lohman) to 6.03 kg (NIR). The results indicated that Lohman skinfold equation provided the most accurate prediction of MW, demonstrating the highest correlation (0.972), lowest MD (0.6 kg), lowest SEE (2.12 kg), and lowest TE (2.25 kg) of the methods evaluated.

Bioelectrical impedance vs. four-compartment model to assess body fat change in overweight adults.

Objective: The Tanita TBF‐305 body fat analyzer is marketed for home and clinical use and is based on the principles of leg‐to‐leg bioelectrical impedance analysis (BIA). Few studies have investigated the ability of leg‐to‐leg BIA to detect change in percentage fat mass (%FM) over time. Our objective was to determine the ability of leg‐to‐leg BIA vs. the four‐compartment (4C) model to detect small changes in %FM in overweight adults.

Cross-validation of the NCAA method to predict body fat for minimum weight in collegiate wrestlers.

ObjectiveIn 1998, the National Collegiate Athletic Association (NCAA) adopted a new rule that required minimum weight testing for collegiate wrestlers. The objective of the study was to cross-validate the method used by the NCAA to estimate minimum weight in collegiate wrestlers. DesignThe NCAA skinfold equation was cross-validated against a criterion value from hydrostatic weighing (HW). SettingThe subjects were tested at the Universities of Wisconsin and Iowa. SubjectsA sample of 93 college wrestlers from the Universities of Wisconsin and Iowa (mean ± SD; age = 20.20 ± 1.67 years, height = 171.98 ± 6.63 cm, weight = 74.44 ± 11.48 kg) were studied. Outcome MeasuresCross-validation included analysis of the standard error of estimate (SEE), total error (TE), and residual plots. ResultsThe mean body fat from the NCAA prediction (10.61 ± 3.58%) was not significantly different than HW (9.70 ± 3.95%). The SEE was low (2.32%), and the TE was low (2.49%). The difference in methods was related to the size of the HW value. The residual plot (y = −0.26x + 3.45, R2 = 0.198) suggests that fat is overestimated in the leaner wrestlers and underestimated in fatter wrestlers. ConclusionThe authors found the NCAA method to be a valid predictor of body fat in this sample of 93 collegiate wrestlers under the conditions of the study. Although some bias was seen across the range of fatness, these data support the NCAA method to estimate body fat in college wrestlers for establishment of minimum weight.

Multicomponent cross-validation of minimum weight predictions for college wrestlers.

UNLABELLED In 1998, the National Collegiate Athletic Association (NCAA) adopted a rule requiring that skinfolds (SF) or hydrostatic weighing (HW) be used to estimate minimum weight (MW) in college wrestlers. PURPOSE To cross-validate the NCAA methods for estimation of MW using a multicomponent criterion (4C). METHODS Criterion MW was calculated from body density (BD), bone mineral content (BMC), and total body water (TBW) using the 4C equation of Lohman (1992). BMC was measured by dual energy x-ray absorptiometry (DXA), TBW by deuterium dilution, and BD by HW. Subjects were Division I athletes from the University of Wisconsin (mean +/- SD; N = 33, age = 19.5 +/- 1.3 yr, height = 177.3 +/- 7.8 cm, weight = 74.2 +/- 9.3kg). RESULTS There was no significant difference between mean MW from HW (69.6 +/- 8.5 kg) and SF (70.1 +/- 8.3 kg) ( P = 0.113), and between mean MW from HW (69.6 +/- 8.5 kg) and 4C (69.5 +/- 8.6 kg) ( P = 0.46). A clinically small, yet significant difference was seen when comparing mean MW from SF to 4C ( P = 0.013). The regression for the relationship between 4C and HW (y = 0.994 x HW + 0.294 kg, R2 = 0.985) and 4C and SF (y = 1.019 x SF - 1.885 kg, R2 = 0.979) did not significantly deviate from the line of identity. Pure error (PE) values of 1.04 kg and 1.35 kg were found for HW and SF, respectively. The difference between the methods was plotted as a function of the 4C criterion. The regression line for HW and 4C (y = -0.009x + 0.743, r = -0.07, P = 0.69) and SF and 4C (y = -0.038x + 3.259, r = -0.27, P = 0.13) suggest that no systematic differences in the prediction were associated with the size of the criterion. CONCLUSION These data support the NCAA methods of HW and SF to predict MW when cross-validated using a 4C criterion in this sample.

Cross-Validation of Methods to Predict Body Fat in African-American and Caucasian Collegiate Football Players

Eight skinfold (SF) equations and bioelectrical impedance analysis (BIA) were cross-validated in 71 Division IA college football players. Criterion percent body fat (%FAT) was determined by hydrostatic weighing (HW) and computed from body density (BD) for African Americans (n = 28) and Caucasians (n = 43). Results were analyzed by method, with position and race effects examined simultaneously using a two-way ANOVA. Analysis included computation of mean difference (MD), correlation (r), standard error of estimate (SEE), and total error (TE). Skinfolds had MDs ranging from -1.8 to 2.9%, correlations from .85 to .93, SEEs from 2.3 to 3.2%, and TEs from 2.3 to 4.2%. Bioelectrical impedance analysis was significantly different from HW and yielded the highest MD (3.8%), lowest correlation (r = .78), highest SEE (3.9%), and highest TE (5.4%). The Jackson and Pollock (1978) SF equation provided the most valid prediction of HW-determined %FAT in a racially mixed sample of college football players, demonstrating the highest correlation, lowest SEE and TE, and an intercept and slope not significantly different than 0.0 and 1.0, respectively.

Measuring aerobic cycling power as an assessment of childhood fitness.

The emergence of obesity, insulin resistance (IR), and type-2 diabetes (T2DM) in children requires a rational, effective public health response. Physical activity remains an important component of prevention and treatment for obesity, T2DM, and IR. Studies in adults show cardiovascular fitness (CVF) to be more important than obesity in predicting IR. We recently demonstrated that a school-based fitness intervention in children who were overweight can improve cardiovascular fitness, body composition, and insulin sensitivity, but it remains unclear whether accurate assessment of fitness could be performed at the school or outside of an exercise laboratory. The purpose of the study was to determine if a new methodology using measurement of cycling power could estimate cardiovascular aerobic fitness (as defined by maximum oxygen consumption; &OV0312;O2max) in middle school children who were over- weight. Thirty-five middle school children who were overweight (mean age 12 ± 0.4 years) underwent testing on a power sensor-equipped Cycle Ops Indoor Cycle (IC), as well as body composition by dual x-ray absorptiometry (DXA), and &OV0312;O2max by tread- mill determination. Insulin sensitivity was also estimated by fasting glucose and insulin. Maximal heart rate (MHR) was determined during &OV0312;O2max testing, and power produced at 80% of MHR was recorded. Spearmans rank correlation was performed to evaluate associations. Mean power determined on the IC at 80% of MHR was 129 ± 77 watts, and average power at 80% MHR divided by total body weight (TBW) was 1.5 ± 0.5. A significant correlation between watts/TBW was seen for &OV0312;O2max (ml/kg/min) (p = 0.03), and significant negative correlation was seen between watts/TBW and fasting insulin (p > 0.05). In middle-school children who were overweight, there was a significant relationship between the power component of fitness and cardiovascular aerobic fitness (measured by &OV0312;O2max). This more accessible and less intimidating field-based measure of power may prove useful in predicting changes in cardiovascular fitness. Thus, accurate assessment of childhood aerobic fitness may be achievable by measurement of power, possibly within the school environment at substantially less cost and effort than laboratory-based measurements.

Effects of Covert Subject Actions on Percent Body Fat by Air-Displacement Plethsymography

Tegenkamp, MH, Clark, RR, Schoeller, DA, and Landry, GL. Effects of covert subject actions on percent body fat by air-displacement plethsymography. J Strength Cond Res 25(7): 2010-2017, 2011—Air-displacement plethysmography (ADP) is used for estimation of body composition, however, some individuals, such as athletes in weight classification sports, may use covert methods during ADP testing to alter their apparent percent body fat. The purpose of this study was to examine the effect of covert subject actions on percent body fat measured by ADP. Subjects underwent body composition analysis in the Bod Pod following the standard procedure using the manufacturers guidelines. The subjects then underwent 8 more measurements while performing the following intentional manipulations: 4 breathing patterns altering lung volume, foot movement to disrupt air, hand cupping to trap air, and heat and cold exposure before entering the chamber. Increasing and decreasing lung volume during thoracic volume measurement and during body density measurement altered the percent body fat assessment (p < 0.001). High lung volume during thoracic gas measures overestimated fat by 3.7 ± 2.1 percentage points. Lowered lung volume during body volume measures overestimated body fat by an additional 2.2 ± 2.1 percentage points. The heat and cold exposure, tapping, and cupping treatments provided similar estimates of percent body fat when compared with the standard condition. These results demonstrate the subjects were able to covertly change their estimated ADP body composition value by altering breathing when compared with the standard condition. We recommend that sports conditioning coaches, athletic trainers, and technicians administering ADP should be aware of the potential effects of these covert actions. The individual responsible for administering ADP should remain vigilant during testing to detect deliberate altered breathing patterns by athletes in an effort to gain a competitive advantage by manipulating their body composition assessment.

BMI z-score in obese children is a poor predictor of adiposity changes over time

BackgroundThe age and sex standardized body mass index (BMIz) is a simple and widely utilized screening tool for obesity in children and adolescents. The purpose of this study was to evaluate the relationship between the BMIz trajectory versus the percent body fat (%FAT) trajectory, and if BMIz could predict significant changes in %FAT in a sample of obese children and adolescents.MethodsIn this longitudinal observational study, body composition was measured by dual energy x-ray absorptiometry (DXA) in obese children within a multidisciplinary pediatric fitness clinic at an academic medical center over a 3-year time period. Regression analyses were conducted to evaluate the association between changes in BMIz and changes in %FAT.ResultsBaseline assessment was obtained from 515 participants. The reduction observed in BMIz (2.20 to 2.08, p < 0.0001) correlated with the reduction in %FAT (38.5 to 35.8%, p < 0.05) in the first two years. The overall correlation between the slope in BMIz reduction versus %FAT reduction was moderate (r = 0.36, p < 0.0001) over the 3-year follow-up period. The sensitivity of BMIz changes for predicting a decrease in %FAT was acceptable (70, 95% CI: 61–78%), however the specificity was poor (42, 95% CI: 31–54%).ConclusionsThese findings advance the understanding of the utility and limitations of BMIz in children and adolescents. While BMIz may be sensitive to changes in adiposity, it is a weak predictor of these changes in total body fat (%FAT) due to the poor specificity. Therefore, clinicians must exercise caution when monitoring changes in a growing child’s body composition to avoid misclassifying or missing substantial change when utilizing BMIz alone.