Aim: Numerous studies report an association between muscle strength and bone mineral density (BMD) in young and older women. However, the participants are generally non-athletes, thus it is unclear if the relationship varies by exercise status. Therefore, the purpose was to examine the relationships between BMD and muscle strength in young women with markedly different exercise levels.
Experimental design: cross-sectional.
Setting: a University research laboratory.
Participants: 18 collegiate gymnasts and 22 age- and weight-matched recreationally active control women.
Measures: lumbar spine, femoral neck, arm, leg and whole body BMD (g/cm(2)) were assessed by dual X-ray absorptiometry. In addition, lumbar spine and femoral neck bone mineral apparent density (BMAD, g/cm(3)) was calculated. Handgrip strength and knee extensor and flexor torque (60 degrees /s) were determined by dynamometry, and bench press and leg press strength (1-RM) using isotonic equipment.
Results: BMD at all sites and bench press, leg press and knee flexor strength were greater in gymnasts than controls (p<0.001). In controls, knee extensor torque was significantly correlated to femoral neck, limb and whole body BMD (r=0.47-0.55, p<0.05), leg press strength was associated with limb and whole body BMD (r=0.52-0.74, p<0.05), and bench press strength with arm BMD (r=0.50, p=0.019). In partial correlations controlling for weight, leg press strength was related to leg and whole body BMD (r=0.46-0.63, p<0.05). There was no association between muscle strength and BMD in gymnasts.
Conclusion: These results suggest that the association between muscle strength and BMD in young women is dependent on exercise status. The osteogenic effect of increased mechanical loading associated with gymnastics training likely contributes to the dissociation of the relationship in gymnasts.