Bone mass and muscle strength in young female soccer players

In this cross-sectional study, bone mass and muscle strength of the thigh w ere investigated in 51 female soccer players, age 16.3 +/- 0.3 years, who h ad been playing soccer for 8.1 +/- 2.1 years and were at the time of the st udy in soccer training for 5.0 +/- 1.7 hours/week. They were compared with 41 nonactive females, age 16.2 +/- 1.3 years. The groups were matched accor ding to age, weight, and height. Areal bone mineral density (BMD) was measu red of the total body, head, lumbar spine, femoral neck, Ward's triangle, a nd the greater trochanter using dual energy X-ray absorptiometry (DXA). Iso kinetic muscle strength of the quadriceps and hamstrings muscles was measur ed using an isokinetic dynamometer. Compared with the nonactives, the socce r players had significantly higher BMD of the total body (2.7%), lumbar spi ne (6.1%), the dominant and nondominant hip tall sites). The largest differ ences were found in the greater trochanter on both sides (dominant, 16.5%, nondominant, 14.8%). The soccer players had significantly higher concentric and eccentric peal; torque of the thigh muscles. In the soccer group, ther e was only a positive association between thigh muscle strength and BMD of the adjacent hip, and in the nonactive group there were several positive as sociations between muscle strength and BMD. However, when adjusting for the variation in weight and height all these associations became nonsignifican t. Using multiple linear regression, the type of activity (soccer player, n onactive) independently predicted BMD of all dominant hip sites (beta = 0.3 2-0.48, P < 0.01). No other variable was found to independently predict BMD of any site. In the younger subjects (less than or equal to 16 years) only BMD of the greater trochanter was significantly higher in the soccer playe rs. In the older subjects (>16 years) the soccer players had significantly higher BMD in all measured sites except for the nonweight-bearing head. The differences in muscle strength between soccer players and nonactives were already seen in the young age group. In conclusion, girls who train and pla y soccer in adolescence have a higher bone mass in the hip and lumbar spine , and a higher muscle strength of the thigh compared with nonactive control s, indicating a site-specific skeletal response of weight-bearing and impac t-loadng acting on the skeleton. The differences in bone mass were already apparent in early adolescence, but became more pronounced in late adolescen ce, probably explained by a longer exposure to soccer training with time. O ur results also indicate that muscle strength in itself might not be of dec isive importance for bone mass in the hip of adolescent females.