Bone volumetric density, geometry, and strength in female and male collegiate runners

PURPOSE: To explore differences in tibial bone geometry, volumetric density, and estimates of bone strength in runners and healthy controls. METHODS: Male (n = 21) and female (n = 38) runners (49.1 ± 13.2 miles•wk) and inactive healthy controls (17 males and 32 females; mean age = 22 ± 3.3 yr) were recruited to participate. Peripheral quantitative computed tomography was used to assess total volumetric bone mineral density (vBMD, mg•mm), total bone area (ToA, mm), and an estimate of compressive bone strength (bone strength index (BSI) = ToA × total bone volumetric density (ToD)) at the distal (4%) site of the tibia. ToA (mm) and cortical bone area (CoA, mm), cortical vBMD (CoD, mg•mm), cortical thickness (CoTh, mm), and an estimate of bone bending strength (polar strength strain index (SSIp), mm) were measured at 50% and 66% sites. RESULTS: ToA and BSI were significantly greater (+11%-19%, P < 0.05) in female runners than controls at the 4% site. At the proximal sites, female runners had significantly greater ToA, CoA, CoTh, and SSIp (+9%-19%, all P < 0.001) compared with female controls. vBMD was similar at all tibia sites. Compared with controls, male runners had significantly greater CoTh at the 50% and 66% sites (+8% and 14%, respectively, P < 0.05) as well as greater CoA (+11%, P < 0.009) at the 66% site. There were no differences in bone strength or density at any site in the male runners. CONCLUSIONS: Greater bone strength in female runners was attributable to greater bone area rather than density. Although male runners did not show greater bone strength, they did exhibit favorable bone geometric properties. These data further document that running has osteogenic potential.