Effects of physical activity on the lean and fat mass of the legs and on the femoral BMD in young adults

Aim. To evaluate the effects of physical activity on the lean (LLM) and fat (FLM) mass of both legs and on the left femur neck bone mineral density (FemBMD) in young adults. Methods. Subjects were 48 healthy male, mean age 25 (range 20-32). Subjects were assigned to one of three groups according to the physical activity practiced from age 10 onwards: 17 sedentary subjects (A), 15 active subjects (B) and 16 athletes (C). LLM and FLM (g) were evaluated by Dual Energy X-ray Absorptiometry (DEXA), as well as FemBMD (g/cm2). The data is shown as mean values ± standard deviation. For the statistical analysis of the data, linear regression analysis and Student's t test for unpaired data were used. Results. No differences were observed between the three groups with regards to age and anthropometric measurements. C had a significantly higher FemBMD than A and B (respectively 1,32+0,2 vs 1,05+0,2, p<0.001 and 1,15+0,2, p<0.01). C had also a significantly (p<0.001) higher LLM than A and B (respectively 23,4+3,4 vs 19,7+2,6 and 19,2+1,9), whereas no differences have been found in FLM. In groups A and B a positive linear correlation between LLM and FemBMD has been found (respectively A: r=0,75, p<0.001; B: r=0,61, p<0.02), while in the group C a positive but not significant correlation (r=0,48, p <0.06) was observed. In all groups no relationship between FLM and FemBMD has been found. Conclusions. In athletes, physical activity, practiced from age 10 onwards, is associated with markedly increased LLM and FemBMD. Our data indicates that LLM is a significant determinant of FemBMD in sedentary and active subjects, while in athletes the increase in LLM does not seem to necessarily affect FemBMD.