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 fat-free mass (FFM) in the lower limbs of young adult male Rugby Union players. Thirty players of mean+/-SD age of 21.1 +/- 2.1 years were recruited. Bone mineral mass, fat mass and lean tissue mass were measured with a Hologic QDR 1000/W whole-body scanner. Anthropometry included circumferences, segmental leg lengths and skinfold thicknesses. Players were divided randomly into prediction (n= 15) and cross-validation (n= 15) samples. Regression equations 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 length with circumferences at the knee (0.7262) and calf (0.7382); the multiple correlation was 0.83 in both instances. Cross-validation statistics found no significant differences (p >0.05) between measured (12.4 +/- 1.5 kg) and 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 measured leg FFM respectively. Correlations between measured and predicted leg FFM were reasonably high (0.79-0.90, p <0.001). The ratio limits of agreement 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 prediction equations tend to be age, gender and population specific, unless validated for other athletic groups, the present equations should be applied to male Rugby Union players with characteristics similar to those described.