Examining the Bone-Muscle Relationship in Male and Female Runners

Abstract

Given the types of loads placed on bone during running, this activity should theoretically have a positive effect on bone strength. Yet several studies suggest runners have normal or low areal bone mineral density (aBMD) compared to nonrunning controls. However, bone geometry can adapt in ways that improve bone strength with no change in bone density or mass. PURPOSE: The purpose of this study is to explore differences in bone geometry, volumetric density, and estimates of bone strength in runners and healthy, inactive controls. METHODS: Peripheral quantitative computed tomography (pQCT, XCT 3000, Orthometrix) was used to assess bone parameters at the radius and tibia in male (n = 21) and female (n = 38) runners and inactive healthy controls (n = 17 males and 32 females), aged 18-35. At the distal sites, total bone density (ToD, mg/mm3) and bone area (ToA, mm2) were measured, and estimated compressive bone strength calculated (BSI = ToA * ToD2). Total (ToA, mm2) and cortical bone area (CoA, mm2), cortical thickness (CTh, mm), density (CoD, mg/mm3) and estimates of strength (SSIp, mm3, Z, mm3) were assessed at the midshaft (50%) and an additional proximal site (66%) of the tibia. Physical activity, health history and miles run per week were assessed by questionnaire. RESULTS: After adjusting for age, weight and tibia length, ToA and BSI (+11-19%) were significantly greater in female runners than controls (p < 0.05) at the 4% site. At the 50 and 66% sites, female runners had significantly (p < 0.001) higher ToA, CoA, CTh, SSIp and Z (+9-34%) compared to female controls. There were no differences between the female runner group and controls at any site for volumetric density values. Compared to controls, male runners had significantly higher CTh (+8−14%, p < 0.05) at the 50% and 66% sites as well as a greater CoA (+11%, p < 0.009) at the 66% site, but no differences in bone strength or density. CONCLUSIONS: The greater bone strength in female runners was due to greater bone area rather than bone density. In contrast, there was no difference in bone strength between male runners and controls; however male runners had more favorable bone geometric properties. These data suggest that running has osteogenic potential.