Validation of near-infrared interactance and skinfold methods for estimating body composition of American Indian women

Purpose: This study tested the predictive accuracy of the Jackson et al. sk infold (SKF equations Sigma 7SKF and Sigma 3SKF), a multi-sire near-infrare d interactance (NIR) prediction equation, and the Futrex-5000 NIR equation in estimating body composition of American Indian women (N = 151, aged 18-6 0 yr). Methods: Criterion body density (D-b) was obtained from hydrodensito metry at residual lung volume. Results: Sigma 7SKF significantly underestim ated D-b (P < 0.05). Sigma 3SKF and Heyward's NIR equations significantly o verestimated D-b (P < 0.05). The Futrex-5000 NIR equation significantly und erestimated percent of body fat (%BF) (P < 0.05). Prediction errors for SKF and multi-site NIR exceeded 0.0080 g.cc(-1). The SEE for Futrex-5000 was 5 .5%BF. Thus, ethnic-specific SKF and NIR equations were developed. For the SKF model, the Sigma 3SKF (triceps, axilla, and suprailium) and age explain ed 67.3% of the variance in D-b: D-b = 1.06198316 -0.00038496(Sigma 3SKF) - 0.00020362(age). Cross-validation analysis yielded r = 0.88, SEE = 0.0068 g .cc(-1), E = 0.0070 g.cc(-1), and no significant difference between predict ed and criterion D-b. For the NIR model, the hip circumference, Sigma 2 Del ta OD2 (biceps and chest), FIT index, age, and height explained 73.9% of th e variance in D-b: D-b = 1.0707606 -0.0009865(hip circumference) -0.0369861 (Sigma 2 Delta OD2) + 0.0004167(height) + 0.0000866(FIT index) -0.0001894(a ge). Cross-validation yielded r = 0.85, SEE = 0.0076 g.cc(-1), E = 0.0079 g .cc(-1), and a small, but significant, difference between predicted and cri terion D-b. Conclusions: We recommend using the ethnic-specific SKF and NIR equations developed in this study to estimate D-b of American Indian women .