Validity of skinfold, bioelectrical impedance and near-infrared interactance equations for assessing changes in fat-free weight

The present study examined the validity of selected skinfold, bioelectrical impedance (BIA), and near-infrared interactance (NIR) equations for assessing changes in fat-free weight (FFW) following 9 weeks of weight training by comparing the estimates to values obtained from underwater weighing (UWW). Fifteen female volunteers (X age $\pm$ SD = 21.5 $\pm$ 2.8 yrs) served as subjects. Validation analyses pre-training and post-training included examination of the constant error, standard error of estimate, r, and total error (TE). FFW (from UWW) increased significantly by 1.7 kg (47.3 to 49.0 kg; p $\u3c$ 0.01) following the training period. The BIA equation, which resulted in a TE value of 2.3 kg, most accurately estimated FFW pre-training, while the sum of 7 skinfold equation was most accurate post-training (TE = 1.5 kg). Correlational analyses performed between the actual and predicted changes in FFW indicated that none of the equations accurately monitored individual changes in FFW (r = $-$0.56 to r = 0.40). Given that the TE values for the prediction equations were generally greater than the changes in FFW and the correlations between the actual and predicted changes were low to moderate, caution should be used when applying skinfold, BIA, and NIR procedures for monitoring training induced increases in FFW