EFFECTS OF PHYSICAL-ACTIVITY, BODY-WEIGHT AND COMPOSITION, AND MUSCULAR STRENGTH ON BONE-DENSITY IN YOUNG-WOMEN

Objective: The purpose of this study was to examine the relationship b etween body weight and composition, muscular strength, physical activi ty, and bone mineral density (BMD) in eumenorrheic college-aged women. Methods: BMD and bone mineral content (BMC) of the total body, and BM D of the lumbar spine (L2-L4) and femoral neck (via dual energy x-ray absorptiometry), as well as body composition and muscular strength, we re measured in 60 college-aged women. The women were divided into thre e groups: 1) low body weight athletes involved in weight-bearing, coll egiate sports (N = 20), 2) matched low body weight and sedentary (N = 20), and 3) average body weight and sedentary (N = 20). All groups wer e matched for height, age, and age at menarche. Results: The athletes had significantly greater (P < 0.05) (mean +/- SD) total body BMD (1.1 64 +/- 0.06 g.cm(-2)), L2-L4 BMD (1.240 +/- 0.13 g.cm(-2)), femoral ne ck BMD (1.144 +/- 0.13 g.cm(-2)) and total body body (2.44 +/- 0.30 kg ) than the low body weight, sedentary (LWS) group, but were only great er than the average body weight sedentary group (AWS) for femoral neck BMD. Significant correlations were found between lean body mass (LBM) and all BMD variables (P < 0.001). A significant correlation (P < 0.0 1) was found between fat mass and all BMD variables in the sedentary s ubjects alone (N = 40), but with inclusion of the athletes (N = 60), n one of the correlations between fat mass and BMD were significant. Arm and leg strength isometric torque values corrected for muscle + bone cross-sectional area (M + B CSA) were not significantly different betw een the athletes and LWS group, but the athletes were greater (P < 0.0 5) than the AWS group for both arm and leg strength/M + B CSA. No sign ificant, site-specific correlations were found between strength/M + B and BMD. Conclusions: In summary, the athletes had significantly great er BMD, BMC, and LBM than the LWS group and, except for a greater femo ral neck BMD, similar BMD, BMC, and LBM as the AWS group. These result s suggest that LBM and weight-bearing exercise both enhance BMD in eum enorrheic young adult women.