Sex differences in muscle health in simulated micro- and partial-gravity environments in rats

Skeletal muscle size and strength are important for overall health for astronauts. However, how male and female muscle may respond differently to micro- and partial-gravity environments is not fully understood. The purpose of this study was to determine how biological sex and sex steroid hormones influence the progression of muscle atrophy after long term exposure to micro and partial gravity environments in male and female rats. Male and female Fisher rats (n ​= ​120) underwent either castration/ovariectomy or sham surgeries. After two weeks recovery, animals were divided into microgravity (0g), partial-gravity (40% of weight bearing, 0.4g), or full weight bearing (1g) interventions for 28 days. Measurements of muscle size and strength were evaluated prior to and after interventions. At 0g, females lost more dorsiflexion strength, plantar flexion strength, and other metrics of muscle size compared to males; castration/ovariectomy did not influence these differences. Additionally, at 0.4g, females lost more dorsiflexion strength, plantar flexion strength, and other metrics of muscle strength compared to males; castration/ovariectomy did not influence these differences. Females have greater musculoskeletal aberrations during exposure to both microgravity and partial-gravity environments; these differences are not dependent on the presence of sex steroid hormones. Correspondingly, additional interventions may be necessary to mitigate musculoskeletal loss in female astronauts to protect occupational and overall health.