Microgravity-induced skeletal muscle atrophy in women and men: implications for long-duration spaceflights to the Moon and Mars.

The inclusion of women on spaceflights has historically been limited. Recently, the first woman who will travel to the Moon was selected, and more women are participating in long-duration spaceflights. However, physiological data from real and simulated microgravity exposure are limited in women. This investigation studied women ( = 8, 34 ± 1 yr) and men ( = 9, 32 ± 1 yr) who underwent 2 (women) or 3 (men) mo of simulated microgravity (6° head-down tilt bed rest). Quadriceps and triceps surae muscle volumes were assessed via MRI before bed rest, (, women and men), (, women), and (, men). Volume of both muscle groups decreased ( < 0.05) in women and men at all bed rest timepoints. Quadriceps muscle volume loss in women was greater than men at 1 mo (: -17% vs. -10%, < 0.05) and this 1-mo loss for women was similar to men at 3 mo (: -18%, > 0.05). In addition, the loss in women at 2 mo (: -21%) exceeded men at 3 mo ( < 0.05). For the triceps surae, there was a trend for greater muscle volume loss in women compared with men at 1 mo (: -18% vs. -16%, = 0.08), and loss in women at 2 mo was similar to men at 3 mo (: -29%, : -29%, > 0.05). The collective evidence suggests that women experience greater lower limb muscle atrophy than men at least through the first 4 mo of microgravity exposure. More sex-specific microgravity studies are needed to help protect the health of women traveling on long-duration orbital and interplanetary spaceflights. This study adds to the limited evidence regarding sex-specific responses to real or simulated microgravity exposure, which collectively suggests a sex-specific muscle atrophy profile, with women losing more than men at least through the first 4 mo of weightlessness. Considering the increase in women being selected for space missions, including the first women to travel to the Moon, more physiological data on women in response to microgravity are needed.