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This study investigated the relationship between isokinetic muscle strength and bone density (SPA and DPA) in men and women aged 45-77 yr. Regression models were adjusted for age, weight, smoking status, and calcium supplementation. Elbow extensors (but not flexors) peak torque was correlated with radial density in men (partial r = 0.26, P < 0.05) and women (partial r = 0.24, P < 0.05). Knee flexor (but not extensor) peak torque in women was significantly correlated with spine density (partial r = 0.28, P < 0.05), and muscle mass was significantly correlated with Ward's triangle density (partial r = 0.35, P < 0.05). No associations between knee flexor or extensor muscle strength and spine or femur bone density were observed in men. Fat-free mass (FFM, hydrodensitometry) was associated with all bone density sites in males and females (partial r = 0.30-0.55; P < 0.05). These results demonstrate that 1) significant associations observed between elbow extensor strength and radial bone density in men and women may reflect loading along the longitudinal axis of the radius associated with elbow extensor activity; and 2) significant associations exist between knee flexor muscle strength and lumbar density in women only. Additionally, the associations between FFM and bone density do not necessarily reflect associations between isokinetic muscle strength and bone density.

The effects of a supervised 1-y walking program and increased dietary calcium (milk supplement, 831 mg/d, vs placebo drink, 41 mg/d) on bones were examined in 36 postmenopausal women (60.2 +/- 6.5 y). Trabecular bone-mineral density (BMD) of the lumbar spine (L1-L3), measured by computed tomography, increased by 0.5% in exercising women (n = 18) and decreased by 7.0% in sedentary women (n = 18; P = 0.02). Femoral-neck BMD measured by dual-photon absorptiometry (DPA) increased by 2.0% in women consuming high dietary calcium (n = 18) and decreased by 1.1% in those on moderate calcium intake (n = 18; P = 0.001). Neither exercise nor dietary calcium had an effect on lumbar spine (L2-L4) measured by DPA, distal radius measured by single-photon absorptiometry, or total body calcium measured by in vivo neutron activation. The varying proportions and rates of turnover of trabecular and cortical bone from one site to another suggest that exercise and high dietary calcium may preferentially alter bone density at different skeletal sites.