Profile of regional fat and fat-free soft tissue accumulation in male athletes

It is unclear whether or not the breakpoint (BP), at which the proportion of each of fat mass (FM) and fat-free soft tissue mass (FFSTM) to body mass (BM) alter, exists in male athletes. We examined the hypothesis that in male athletes, the regional FM and FFSTM-BM relationships have a BP, but the body mass at BP (BM_BP) differs among the arms, trunk, and legs.

By using a dual X-ray absorptiometry, whole-body and regional FMs and FFSTMs in the arms, trunk, and legs were estimated in 198 male athletes (20.8 ± 2.1 years; 1.73 ± 0.07 m; 72.7 ± 14.8 kg). To detect the BP in the relationship between each of FM and FFSTM and BM, a piecewise linear regression analysis was used. If a BP was detected in the corresponding relationship, the significant difference between the regression slopes above and below the BP was examined.

The regression analysis indicated that the BM_BP existed in the FM- and FFSTM-BM relationships regardless of region and whole body. For the whole body, BM_BP was 81.8 kg for FM and 82.2 kg for FFSTM. In regional FM-BM relationships, BM_BP was 80.5 kg for arms, 82.6 kg for trunk, and 63.3 kg for legs, and the regression slopes above the BM_BP became higher than those below the BP, and vice versa in regional FFSTM-BM relationships (BM_BP 104.6 kg for arms, 80.9 kg for trunk, and 79.0 kg for legs). The relative differences in the slopes between below and above BM_BP in the regional FM-BM relationships were higher in the arms and trunk than in the legs, and those in the regional FFSTM-BM relationships in the legs than in the trunk.

Whole-body and regional FM- and FFSTM-BM relationships for male athletes have breakpoints at which the proportion of the tissue masses to BM alters. The BM_BP and differences in the distribution of regional FM and FFSTM around the breakpoint are region specific.