Mechanical loading is required for maintenance of the musculoskeletal system. Thus, exposure to microgravity induces marked bone loss in both humans and animals, and is a major concern for astronauts exposed to long-duration spaceflight, as they may be at increased risk for skeletal fragility and bone fractures. Most prior studies have relied on dual-energy X-ray absorptiometry (DXA), a 2D technique used to assess bone mass at different skeletal sites, to assess effects of spaceflight on bone strength and fracture risk. However, DXA-based measurements are limited in several regards. Newer technologies, including 3D quantitative computed tomography (QCT) are able to overcome the limitations of DXA. Moreover, QCT images can be used to estimate bone strength using a standard engineering approach called finite element analysis. Indeed, QCT images have been used successfully to demonstrate negative effects of spaceflight on hip bone density and strength. However, a similar examination of the effects of spaceflight on vertebral strength has not been performed. Thus the degree of spinal deconditioning and subsequent risk of vertebral fracture following long-duration spaceflight remains unknown.
Specific Aims:
1) Determine changes in bone density and vertebral strength following long-duration spaceflight in astronauts and cosmonauts, including pre-flight, post-flight, and one-year after return to Earth
2) Use musculoskeletal modeling to compute subject-specific spinal loading and estimate the risk of vertebral fracture (as the load-to-strength ratio) following long-duration spaceflight
3) Determine changes in trunk muscle size and density following long-duration spaceflight.
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