Body measurement variability, fatness, and fat-free mass in children 8, 11, and 14 years of age: Project HeartBeat!

Project HeartBeat! is a four year mixed-longitudinal study of the developme nt of cardiovascular risk factors in White and African American children wh o at baseline comprised three age cohorts 8, 11, and 14 years. This paper f ocuses on the anthropometric variables which were chosen to reflect body fa t and fat-free mass. Selected anthropometric dimensions are compared with t hose of samples from the combined National Health and Nutrition Examination Surveys I and II to explore the similarities of the samples in terms of ce ntral tendencies and variances. The measurements were then explored in term s of their ability to estimate the two compartment model of body compositio n: fat-free mass (FFM) and body fat (BF) from bioelectrical impedance (BIA) . Project HeartBeat! children are slightly larger than NHANES children and have variances that are generally comparable to the national surveys. Over seven percent (7.7%) of children were overweight (BMI) and 25% had 'mild ob esity' by %BF. Three different factor analytic methods (incomplete principa l components, alpha and maximum likelihood) produced two latent variables f rom 17 anthropometric dimensions which together accounted for 76-83% of the variation: (1) A body mass factor (F1) which was weighted highly on six ci rcumferences, weight and six skinfolds, and (2) a linear growth factor (F2) which was strongly associated with height, arm length, and sitting height. Triceps, subscapular and midaxillary skinfolds were consistently highly lo aded on the body mass factor and their sum was highly correlated to %BF and fat mass (0.90-0.99). This suggests that this sum could be used to estimat e fatness in children in studies where the BIA or other body composition te chniques are unavailable. FFM and %BF were predicted from the anthropometri c factors. Both factors contributed to the estimate of FFM (R-2 = 0.81-0.93 ), although F2 contributed proportionately more. The 'body mass' factor (F1 ) was the main predictor of %BF (R-2 = 0.86-0.93), though at some ages the linear factor (F2) was significantly and negatively related to %BF. This se t of anthropometric dimensions, taken for the purpose of estimating body co mposition and summarized as two latent vectors by factor analysis, strongly reflects body fat and FFM in children and adolescents. (C) 1999 Wiley Liss , Inc.