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The purpose of this study was to assess the predictability of body fatness as determined by three separate approaches: (1) body density from hydrostatic weighing and functional residual volume alone (PFD); (2) body density and water (PFDW); (3) body density, water and bone mineral (PFDWB). Bone mineral was estimated from radius and ulna measurements using photon absorptiometry, and total body water was estimated using deuterium oxide dilution. N ine skinfolds were taken with a Harpenden caliper. A 4 X 2 X 2 factorial plan was used representing four maturation groups (based on secondary sex characteristics) males and females, black and white subjects. The sample consisted of 310 subjects children and adults ranging in age from 8-29 years. In the prepubescent and pubescent groups of children, systematic differences were found among methods with the PFD alone producing higher mean density values than the other two estimates.

Constants were fitted by the least squares method in a step down multiple regression analysis to determine which skinfold measurements most accurately predicted PFDWB. The systematic effects of racial group, sex, and maturation were also included in the analysis. The R2 and SEE from sum of triceps and calf and sum of triceps and calf squared plus design variables in prepubescent group were substantially lower for each of the three PFD estimates compared to the other three groups. When PF estimate was determined from PFDWB rather than PFD alone the R2 increased from 62% to 77% and the SEE dropped from 4.5 to 3.9%, lending support to the concept that constants used to estimate fat in adults tend to overestimate body fatness in children. Curvilinear equations for the prediction of PFDWB are presented for triceps and subscapular skinfolds and linear equations for triceps and calf skinfolds taking into account the effects of maturation level, race and sex. These equations may provide more accurate estimates of PF than those currently available, since they take into consideration the use of a multicomponent approach to body composition and account for the chemical immaturity of children.