Density of the fat-free mass and estimates of body composition in male weight trainers

The purpose of this study was to determine whether the assumed density and composition of the fat-free mass (FFM) and estimates of percent fat (%Fat) from body density by use of the Siri equation (%Fat(d)) are valid in weight trainers with high musculoskeletal development. Measures of body density by underwater weighing (D-b), body water by deuterium dilution, and bone mineral by whole body dual-energy X-ray absorptiometry were obtained in young white men: 14 weight trainers with high musculoskeletal development and 14 non-weight-training controls with average musculoskeletal development. %Fat(d) was significantly higher (P less than or equal to 0.05) than %Fat estimated from body density, water, and mineral (%Fat(d,w,m)) by use of a four-component model in weight trainers (17.3 +/- 4.6 vs. 13.2 +/- 5.1%) but not in controls (14.8 +/- 3.1 vs. 14.2 +/- 3.6%). The greater discrepancy between %Fat(d) and %Fat(d,w,m) was explained by lower density of fat-free mass (D-ffm) in weight trainers (1.089 +/- 0.005 g/ml) than in controls (1.099 +/- 0.007 g/ml). The lower D-ffm, in the weight trainers was due to higher water (74.8 +/- 1.2 vs. 72.6 +/- 2.0%) and lower mineral (5.3 +/- 0.6 vs. 5.9 +/- 0.4%) and protein (19.9 +/- 1.4 vs. 21.5 +/- 1.9%) fractions of the FFM. We conclude that, in young white men with high musculoskeletal development, D-ffm is lower than the assumed value of 1.1 g/ml and %Fat is overestimated from D-b by use of the Siri equation.