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The purpose of these analyses was to explore whether physical activity score, leg power or grip strength were associated with tibia and radius estimates of bone strength, cortical density, or total bone area. Peripheral quantitative computed tomography (pQCT) was used to compare tibial and radial bone volumetric density (vBMD, mg/cm(3)), total (ToA, mm(2)) and cortical (CoA, mm(2)) bone area, and estimates of bone compressive strength (bone strength index, BSI) and bending strength (polar strength strain index, SSIp) in a subset (n=1171) of men (> or = 65 years) who participated in the multi-site Osteoporotic Fractures in Men (MrOS) study. Physical activity was assessed by questionnaire (PASE), leg power by Nottingham Power Rig, and grip strength by a hand-held Dynamometer. Participants were categorized into quartiles of PASE, grip strength or leg power. The model was adjusted for age, race, clinic, weight, and limb length. In the tibia, BSI (+7%) and SSIp (+4%) were highest in the most active physically quartile compared to the least active (p<0.05). At the 4% site of the tibia, men with the greatest leg power had both greater ToA (+5%, p<0.001) and BSI (+5.3%, p=0.086) compared to men with the least leg power. At the 66% site of the tibia, the men with the highest leg power, compared to the men with the lowest leg power, had greater ToA (+3%, p=0.045) SSIp (+5%, p=0.008). Similar results were found at both the distal and midshaft of the radius. The findings of this study suggest the importance of maintaining levels of physical activity and muscle strength in older men to prevent bone fragility., (Copyright 2010. Published by Elsevier Inc.)