Estimating fat-free mass in recreationally resistance-trained young men: Longitudinal and cross-sectional validation of different methods.

Several techniques exist to measure fat-free mass (FFM). Accordingly, this study is based on data from our recent trial comparing the sensitivity of the main field methods available with that of dual-energy X-ray absorptiometry (DXA) as reference and analyzing the cross-sectional accuracy of these field methods in recreationally resistance-trained males. We hypothesized that the use of these techniques would lead to varying estimates of FFM compared with DXA. Participants (N = 23; 21.4 ± 3.3 years) completed a 10-week resistance training plus diet intervention designed to optimize hypertrophy. FFM was determined by bioelectrical impedance analysis (BIA), 23 anthropometric equations, and DXA. After the intervention, FFM increased significantly according to BIA and most anthropometric estimates, but this increase was not detected by 2 anthropometric equations or by DXA. Only 1 of these 2 equations showed significant correlation with DXA and no standardized or significant differences to this reference method, although it did display significant heteroscedasticity. In our cross-sectional analysis, only 1 anthropometric equation gave rise to good accuracy as confirmed by DXA. Our findings indicate that the use of different techniques to assess FFM gains in response to a hypertrophic intervention yields different results. BIA with general embedded equations should not be used to monitor a young male adult's body composition. To monitor FFM over time, we would recommend the Dunne et al. equation (2) as the most sensitive field method, and to assess FFM cross-sectionally, equation (1) of these authors is the most accurate field method. This study compares the sensitivity and the cross-sectional accuracy of BIA and anthropometry using DXA as a reference in resistance-trained males. Fat-free mass was significantly increased according to BIA and to most anthropometric estimates, but not according to 2 anthropometric equations or to DXA. Anthropometric equations (1) and (2) of Dunne et al. [20] reported the best sensitivity and the best accuracy, respectively. BIA, bioimpedance analysis; DXA, dual-energy X-ray absorptiometry [Display omitted] [ABSTRACT FROM AUTHOR]