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 (SSI(p)) 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