Reliability and validity of body composition measures in female athletes

The purpose of this investigation was to determine the reliability and vali dity of bioelectrical impedance (BIA) and near-infrared interactance (NIR) for estimating body composition in female athletes. Dual-energy X-ray absor ptiometry was used as the criterion measure for fat-free mass (FFM). Studie s were performed in 132 athletes [age = 20.4 +/- 1.5 (SD) yr]. Intraclass r eliabilities (repeat and single trial) were 0.987-0.997 for BIA (resistance and reactance) and 0.957-0.980 for NIR (optical densities). Validity of BI A and NIR was assessed by double cross-validation. Because correlations wer e high (r = 0.969-0.983) and prediction errors low a single equation was de veloped by using all 132 subjects for both BIA and NIR. Also, an equation w as developed for all subjects by using height and weight only. Results from dual-energy X-ray absorptiometry analysis showed FFM = 49.5 +/- 6.0 kg, wh ich corresponded to %body fat (%BF) of 20.4 +/- 3.1%. BIA predicted FFM at 49.4 +/- 5.9 kg (r = 0.981, SEE = 1.1), and NIR prediction was 49.5 +/- 5.8 kg (r = 0.975, SEE = 1.2). Height and weight alone predicted FFM at 49.4 /- 5.7 kg (r = 0.961, SEE = 1.6). When converted to %BF, prediction errors were similar to 1.8% for BIA and NIR and 2.9% for height and weight. Result s showed BIA and NIR to be extremely reliable and valid techniques for esti mating body composition in college-age female athletes.