Forearm muscle size, strength, force, and power in relation to pQCT-derived bone strength at the radius in adults

We aimed to examine the relationship between forearm muscle cross-sectional area (MCSA), muscle force, or rate of torque development (RTD) and 2 estimated radius bone strength indices - compressive bone strength index (BSI) at the wrist and strength strain index in torsion (SSIp) at the shaft - in healthy middle-aged males and females. Distal (4%) and shaft (65%) sites of nondominant forearms were scanned using peripheral quantitative computed tomography (pQCT) in a sample of 48 adults (mean age +/- SD, 49.4 +/- 2.4 y) to obtain estimated bone strength indices and MCSA. Muscle force, measured by grip dynamometry and wrist flexion RTD, was obtained using an isokinetic dynamometer. Hierarchical linear regressions, adjusted for weight, explained 27% and 36% of the BSI variance at the 4% site in males and premenopausal females, respectively (p < 0.05). At the radius shaft, weight explained 26% (p < 0.05) and 83% (p < 0.01) of SSIp variance. The unique variance of BSI explained by MCSA was 16% in males (p < 0.05) and 31% in females (p < 0.01). Grip force predicted variance in SSIp in males (p < 0.01) and BSI in females (p < 0.05). RTD did not explain any variance in BSI or SSIp. Body weight was the only significant predictor (p < 0.05) of SSIp in females. Although forearm muscle size and grip strength are associated with estimates of radius bone strength at midlife, this relationship appears to be sex dependent. The differences observed between muscle size and strength properties and bone strength at distal and shaft sites of the radius suggest a property-, sex-, and site-specific relationship between muscle and bone in the forearm.