Calf Muscle Volume and Fat Fraction Changes Following Bedrest

Motivation: An increased interest in human spaceflight motivates studying musculoskeletal changes associated with unloading, and potential exercise countermeasures to address these changes. Goal(s): To determine (1) if lower leg muscle volume and fat fraction change following 14-day head-down bedrest and (2) if an exercise countermeasure modifies these changes. Approach: A Dixon-based approach was used to measure muscle volume and fat fraction before bedrest and three timepoints after bedrest. Results: Muscle volume decreased and fat fraction increased immediately after bedrest and then recovered towards baseline values at subsequent timepoints (p<0.05). The exercise countermeasure did not significantly modify these changes Impact: Lower leg muscle volume decreases and fat fraction increases after periods of unloading due to bedrest. While most muscles return to pre-bedrest levels after a month, exercise countermeasures should be further developed to moderate or eliminate this initial loss.