Fat-free Mass Characteristics of Muscular Physique Athletes

Simple body composition models, such as two-compartment models, use assumptions which may be violated in specific athletic populations (e.g., the constancy of fat-free mass density [DFFM] and hydration [TBW:FFM]). The present analysis examined FFM characteristics of muscular physique athletes.

Twenty-six athletes (16 males: 94.5 ± 9.9 kg, 12.2% ± 4.2% fat; 10 females: 63.8 ± 5.7 kg, 19.7% ± 4.9% fat) completed duplicate assessments of dual-energy x-ray absorptiometry (DXA), bioimpedance spectroscopy (BIS), and single-frequency and multifrequency bioelectrical impedance analysis (SFBIA; MFBIA). Fat-free mass was calculated via five-compartment (5C) model, and FFM characteristics (i.e.

FFM, FFM mineral, FFM protein) were compared between sexes and between the sample and reference values (RV) from cadaver analysis.

FFM5C was designated as the reference TBW:FFM model, and alternate models were produced using BIS, MFBIA, SFBIA, impedance-based equations, and DXA output.

Males had lower TBW:FFM and FFM mineral, but higher FFM protein than females (P < 0.05). DFFM was significantly lower than RV in males (1.096 ± 0.006 g·cm, RV: 1.103 ± 0.013 g·cm; P < 0.001) and appeared higher in females (1.093 ± 0.012 g·cm, RV: 1.087 ± 0.021 g·cm; P = 0.17). TBW:FFM did not differ from RV in females (75.3% ± 4.0%; RV, 75.7% ± 4.4%; P = 0.74) or males (72.7% ± 1.9%; RV, 72.7% ± 3.1%; P = 0.97). Fat-free mass mineral was lower than RV in males (5.5% ± 0.4%; RV, 6.8% ± 0.8%; P < 0.001) and higher in females (6.5% ± 0.5%; RV, 6.1% ± 0.8%; P = 0.04). Fat-free mass protein was significantly greater than RV in males (21.9% ± 1.8%; RV, 20.6% ± 2.6%; P = 0.014), but the difference from RV in females was not statistically significant (18.3% ± 4.1%; RV, 17.1% ± 4.5%; P = 0.39). Alternate TBW:FFM models varied substantially in their agreement with RV.

The FFM characteristics were shown to differ between male and female physique athletes. These results may have implications for optimal body composition assessment methods when atypical physique characteristics are present.