A new study examines how variations in the strength of gravity affect muscle health in mice aboard the International Space Station. The work pinpoints 0.67g as a turning point – lower than this, and muscle begins to deteriorate. The research also identifies 11 metabolites that change as gravity weakens. These metabolites could be used as biomarkers to monitor muscle health in astronauts one day, Ryosuke Tsuji and colleagues suggest. It’s well known that spaceflight changes the musculoskeletal system. For example, in microgravity, the molecular processes that govern muscle health begin to go haywire. Now, Tsuji et al. ask: is there a specific level of gravity at which muscle deterioration begins? They examined 24 male mice aboard the International Space Station across a range of artificial gravity settings, exposing the animals to microgravity, 0.33g, 0.67g, and 1g conditions for up to 28 days. Then, they looked at changes to the animals’ grip strength and atrophy of the soleus, a hindlimb muscle that is particularly sensitive to changes in gravity. Results revealed that 0.33g was enough gravity to prevent full muscle atrophy. However, muscle myofibers did change in composition. At the higher value of 0.67g, muscles showed no deterioration in function nor change in myofiber concentrations. “Considering that a journey to Mars would require approximately 8 to 9 months, it is essential to assess whether the protective effects observed here will persist during extended spaceflight,” Tsuji et al. write. They subsequently performed metabolomics on plasma from mice, discovering 11 metabolites that varied based on gravity conditions. With further research, these might provide useful indicators of muscle deterioration in astronauts.
For journalists monitoring how spaceflight alters the body, a 2026 Science Advances study involving ISS experiments pinpointed specific intracellular RNA alterations associated with known space travel-related health issues: www.science.org/doi/10.1126/sciadv.adw7832
