Validity of near-infrared interactance for estimating relative body fat in female high school gymnasts

The present investigation examined the validity of near-infrared interactance (NIR) estimates of relative body fat (% fat) from the Futrex-5000 (F5000), Futrex-5000 A (F5000 A), and Futrex-1000 (Fl000) instruments. Ninety-eight female high school gymnasts (X̄ age ± SD = 15.7 ± 1.2 yr) participated in this investigation. Subsamples were used to cross-validate the F5000 (n = 52), F5000 A (n = 46), and F1000 (n = 89) instruments. The NIR % fat estimates were validated against criterion % fat from underwater weighing (UWW) using the adult conversion constants of Brozek et al. (6) (UWWB) and the female age-specific constants of Lohman (23) (UWWL). The cross-validation statistical analysis included examination of the constant error (CE), standard error of estimate (SEE), r, and total error (TE). In addition, full-model multiple regression analyses were used to predict UWWB or UWWL from body weight (BW) and height (HT). BW and HT were correlated with % fat at R = 0.65-0.70, while the validity coefficients for the NIR instruments ranged from r=0.40-0.78. The F5000 resulted in nonsignificant CE values (- 0.3% fat vs UWWB and 1.5 % fat vs UWWL; p > 0.008) as well as the lowest TE values (TE = 3.1% fat vs UWWB and 4.0% fat vs UWWL). All other NIR estimates of % fat resulted in TE values ≤ 6.3% fat. In addition, for all NIR instruments there were negative correlations for the plots of the CE versus the mean of predicted and criterion (UWWB and UWWL)% fat. Therefore, the present findings indicated that the F5000 provided more accurate estimates of % fat than the F5000 A or F1000 instruments, but may underestimate the desired minimal body weight for female gymnasts at the low end of the % fat distribution.