Assessing the Body Composition of 6-17 Year-old Black and White Girls in Field Studies

The purpose of the study was to develop ethnic-specific equations for fat-free mass (FFM) from selected anthropometric dimensions and bioelectrical impedance measures of resistance (R) and reactance (Xc) for use in the NHLBI Growth and Heath Study. Using dual-energy X-ray absorptiometry measures of body composition as the dependent variable and field measures of body composition by anthropometry and bioelectrical impedance as the explanatory variables, ethnic-specific prediction equations were developed on a sample of girls representing a wide range of ages and BMI. The equations were cross-validated using (1) the Prediction of Sum of Squares (PRESS) statistic and (2) an independent sample of 20 girls of each race from a study conducted at the National Institute of Child Health and Human Development (NICHD). Subjects were 65 White and 61 Black girls 6-17 years of age. The best race-specific equations for FFM each explained 99% and 97% of the variance in the White and Black girls, respectively. Root mean square errors (RMSE) ranged from 1.14 to 1.95 kg. The equation for Black girls used Stature2/Resistance (R), weight, and reactance (Xc) as predictor variables; the equation for White girls used Stature2/R, weight, and triceps skinfold thickness. The results indicate that (1) equations to predict FFM in girls should be ethnic-specific and that (2) accurate values for TBF and %BF can be calculated from the predicted FFM

Replicability for Anthropometry in the Elderly

Anthropometric data were collected in a sample of healthy adults (23 men and 21 women), 54 to 85 years of age. Compared to groups of younger individuals, these older adults have more frequent and larger inter-observer errors for most body measurements. Repeated measurements reduce the incidence of large inter-observer differences for measures of body size. Accurate anthropometry is important because of relationships to body stores of fat and muscle

Associations Between Bioelectric Impedance and Anthropometric Variables

Associations of bioelectric resistance with anthropometric pa­rameters for stature, weight, upper arm and calf circumferences, and seven skinfold thicknesses were analyzed in 153 young, White men and women. Bivariate correlations of resistance with weight and upper arm and calf circumferences were negative and statistically significant in each sex. There were small, but significant, negative correlations between resistance and subscapular and midaxillary skinfold thicknesses in men, and subscapular, midaxillary, paraumbilical and biceps skinfold thicknesses in women. Step­wise maximum R2 regressions demonstrated that 72% and 75% of the vari­ance in resistance in men and women, respectively, were predicted by stature, weight (in women only), upper arm and calf circumferences, and mean skinfold thickness. Standard errors of prediction were approximately 5.5% (25 ohms) in men, and 5.9% (34 ohms) in women. An index of adipose tissue distribution, log(subscapular/lateral calf) skinfold thick­nesses, was not associated with resistance in either sex

The Influence of Physiologic Variables and Oral Contraceptiveson Bioelectric Impedance

In the present study, three groups of young adults (N=4, N=153, N = 29) were used separately or together to test for the effects of diurnal variation, of diet or physical activity on bioelectric impedance and of the possible changes in bioelectric impedance during the menstrual cycle in women taking oral contraceptives and in women not taking oral com traceptives. In young adults of normal stature and weight, there was no significant association between measures of bioelectric resistance and time- of-day or between interval from previous meal or drink and means of the differences of body composition variables estimated from underwater weigh\u27 ing less corresponding values predicted from sex-specific equations using bioelectric resistance and anthropometry. In the women who did not par­ticipate in some form of regular physical activity, the means of the dif­ferences of body composition variables estimated from underwater weighing less corresponding values predicted from bioelectric resistance and an­thropometry were significantly different from corresponding mean dif­ferences for women who did participate in some form of regular physical activity. The corresponding findings in the men were not significant. Also, the effects of oral contraceptive usage, and of the timing within the men­strual cycle on measures of bioelectric resistance were not significant. Ex­cept for the effect of the absence of exercise in the women, the effects of the physiologic variables and oral contraceptive usage upon bioelectric imped­ance were not significant

Longitudinal Trends of Weight/Stature2 in Childhood in Relationship to Adulthood Body Fat Measures

The degree of continuity from childhood to adulthood in body fatness is evaluated using the results of longitudinal principal components analysis of W/S2 during childhood (3 months-18 years) in relation to several adult measures of body fatness (W/S2 at 30 years, total body fat, per cent body fat, fat cell number, fat cell size, and weight change from 18 to 30 years). Sixty per cent or less of the variance in any of the adult outcomes is explained by trends in W/S2 during childhood represented by the components. The largest amounts of variance are explained for W/S2 at 30 years, total body fat and per cent body fat. Ten to fifteen per cent of the variance in fat cell number is explained by the components. Weight change between from 18-30 years and fat cell size are not significantly associated with trends in W/S2 during childhood. These results suggest that a significant proportion of the variance in adulthood body fatness is determined by influences beginning after maturity is reached