Athletes participating in sports characterized by specific loading modalities have exhibited different levels of augmentation of bone properties; however, the extent to which these loading environments affect bone micro-architecture and estimated bone strength (i.e., bone quality) remains unclear. Furthermore, the relative role of impact loading versus loading due to muscle forces in determining bone properties is confounded. The objectives of this study were 1) to examine the role of impact loading on bone quality of the distal radius and distal tibia in elite athletes, as determined by high resolution peripheral quantitative computed tomography (HR-pQCT) and finite element analysis (FEA), and 2) to investigate the relationship between bone quality and muscle strength in elite athletes. Ninety-five females (n=59) and males (n=36) between the ages of 16-30 years participated in the study. Participants included alpine skiers (high-impact), soccer players (moderate impact), swimmers (low-impact), and non-athletic controls. All group comparisons were made after accounting for age, height, and body mass. As expected, minimal differences in HR-pQCT parameters across groups were observed at the non weight-bearing distal radius. At the weight-bearing distal tibia, female alpine skiers and soccer players had significantly higher bone density, cortical thickness, and failure load (i.e., bone strength (N) in compression estimated by FEA) than swimmers (p<0.05). Female alpine skiers also had lower trabecular separation than swimmers and controls. Male alpine skiers had 20% higher trabecular bone mineral density than swimmers, and male soccer players exhibited 22% higher trabecular number than swimmers at the distal tibia (p<0.05). Male alpine skiers and soccer players had 28-38% higher failure load at the distal tibia than swimmers. No differences in bone parameters were observed between swimmers and controls for either sex at either site. Both muscle strength and sporting activity were predictors of failure load at the distal tibia in the female cohort. Sporting activity, but not muscle strength, was a significant predictor of failure load in the male cohort at both the radius and tibia. This data suggests that impact loading in sporting activity is highly associated with bone quality. Longitudinal and interventional studies are required to further clarify the muscle-bone interaction.

Objectives Bone loss remains a primary health concern for astronauts, despite in-flight exercise. We examined changes in bone microarchitecture, density and strength before and after long-duration spaceflight in relation to biochemical markers of bone turnover and exercise. Methods Seventeen astronauts had their distal tibiae and radii imaged before and after space missions to the International Space Station using high-resolution peripheral quantitative CT. We estimated bone strength using finite element analysis and acquired blood and urine biochemical markers of bone turnover before, during and after spaceflight. Pre-flight exercise history and in-flight exercise logs were obtained. Mixed effects models examined changes in bone and biochemical variables and their relationship with mission duration and exercise. Results At the distal tibia, median cumulative losses after spaceflight were −2.9% to −4.3% for bone strength and total volumetric bone mineral density (vBMD) and −0.8% to −2.6% for trabecular vBMD, bone volume fraction, thickness and cortical vBMD. Mission duration (range 3.5–7 months) significantly predicted bone loss and crewmembers with higher concentrations of biomarkers of bone turnover before spaceflight experienced greater losses in tibia bone strength and density. Lower body resistance training volume (repetitions per week) increased 3–6 times in-flight compared with pre-spaceflight. Increases in training volume predicted preservation of tibia bone strength and trabecular vBMD and thickness. Conclusions Findings highlight the fundamental relationship between mission duration and bone loss. Pre-flight markers of bone turnover and exercise history may identify crewmembers at greatest risk of bone loss due to unloading and may focus preventative measures.