Prediction and validation of fat-free mass in the lower limbs of young adult male Rugby Union players using dual-energy X-ray absorptiometry as the criterion measure

The aim was to derive and cross-validate prediction equations to estimate f at-free mass (FFM) in the lower limbs of young adult male Rugby Union playe rs. Thirty players of mean+/-SD age of 21.1 +/- 2.1 years were recruited. B one mineral mass, fat mass and lean tissue mass were measured with a Hologi c QDR 1000/W whole-body scanner. Anthropometry included circumferences, seg mental leg lengths and skinfold thicknesses. Players were divided randomly into prediction (n= 15) and cross-validation (n= 15) samples. Regression eq uations were derived from the prediction sample and validated on the cross- validation sample. Seven equations were formulated to predict leg FFM. The two equations providing the lowest standard errors of estimate were leg len gth with circumferences at the knee (0.7262) and calf (0.7382); the multipl e correlation was 0.83 in both instances. Cross-validation statistics found no significant differences (p >0.05) between measured (12.4 +/- 1.5 kg) an d predicted leg FFM (12.1-12.4 kg). The smallest mean difference was -0.05 kg, the largest 0.26 kg; these were equivalent to -0.4 and 2.1% of the meas ured leg FFM respectively. Correlations between measured and predicted leg FFM were reasonably high (0.79-0.90, p <0.001). The ratio limits of agreeme nt confirmed that there was little bias between measured and predicted leg FFM (1.00-1.02) and a good level of agreement (1.12-1.16). Because predicti on equations tend to be age, gender and population specific, unless validat ed for other athletic groups, the present equations should be applied to ma le Rugby Union players with characteristics similar to those described.