Bone geometry, strength, and muscle size in runners with a history of stress fracture

PURPOSE: Our primary aim was to explore differences in estimates of tibial bone strength, in female runners with and without a history of stress fractures. Our secondary aim was to explore differences in bone geometry, volumetric density, and muscle size that may explain bone strength outcomes. METHODS: A total of 39 competitive distance runners aged 18-35 yr, with (SFX, n = 19) or without (NSFX, n = 20) a history of stress fracture were recruited for this cross-sectional study. Peripheral quantitative computed tomography (XCT 3000; Orthometrix, White Plains, NY) was used to assess volumetric bone mineral density (vBMD, mg•mm), bone area (ToA, mm), and estimated compressive bone strength (bone strength index (BSI) = ToA × total volumetric density (ToD)) at the distal tibia (4%). Total (ToA, mm) and cortical (CoA, mm) bone area, cortical vBMD, and estimated bending strength (strength-strain index (SSIp), mm) were measured at the 15%, 25%, 33%, 45%, 50%, and 66% sites. Muscle cross-sectional area (MCSA) was measured at the 50% and 66% sites. RESULTS: Participants in the SFX group had significantly smaller (7%-8%) CoA at the 45%, 50%, and 66% sites (P ≤ 0.05 for all), significantly lower SSIp (9%-10%) at the 50% and 66% sites, and smaller MCSA (7%-8%) at the 66% site. The remaining bone parameters including vBMD were not significantly different between groups. After adjusting for MCSA, there were no differences between groups for any measured bone outcomes. CONCLUSIONS: These findings suggest that cortical bone strength, cortical area, and MCSA are all lower in runners with a history of stress fracture. However, the lower strength was appropriate for the smaller muscle size, suggesting that interventions to reduce stress fracture risk might be aimed at improving muscle size and strength.