These Space-Faring Mice Are Helping Scientists Figure Out How to Keep Astronauts’ Muscles Working Properly

A new study suggests a gravity threshold for maintaining muscle function

Sara Hashemi | Daily Correspondent

March 16, 2026

Share

Copy linkEmailSMSFacebookXRedditLinkedInBlueskyPrint

Add as preferred source

Just a handful of people have spent a consecutive year or more in space. But NASA aims to up that timeframe drastically with its goal of sending astronauts to Mars—a round trip estimated to take several years—as early as the 2030s.

However, human bodies weren’t made for extended stays in space; without Earth’s gravity, for instance, our muscles weaken. That’s why in 2023, researchers launched mice to the International Space Station (ISS), where they stayed in varying levels of gravity for about a month. The findings, published March 13 in the journal Science Advances, hint at the amount of gravity needed to maintain astronauts’ muscles, and suggest that the level on Mars won’t cut it.

“While we can simulate spaceflight on Earth in humans, it’s extremely complicated and costly,” says study co-author Marie Mortreux, a physiologist at the University of Rhode Island, in a statement. “We have centrifuges that can be used to temporarily expose humans to certain gravity levels, but it is not homogenous nor constant.”

In mid-March 2023, 24 mice lifted off from NASA’s Kennedy Space Center in a SpaceX Dragon capsule as part of a resupply mission to the ISS. Once the creatures arrived, researchers split them into four groups and placed them into chambers with four levels of gravity: microgravity, or the condition in space; 1 g, which is what we experience on Earth; 0.67 g and 0.33 g. The last level is close to Mars’ gravity, which is about 0.38 g.

The space-faring mice spent about 28 days in those conditions before returning to Earth in April. Mortreux and her colleagues then analyzed the weight, strength and movement of the 23 surviving animals and compared them with their preflight measurements and those of mice that stayed on Earth.

Analyses revealed that mice that spent time in microgravity or 0.33 g had reduced forelimb grip strength after their journey to space. They also showed deterioration in a leg muscle that’s particularly sensitive to gravity. Mice kept at 0.67 g, however, maintained their grip strength and their gravity-sensitive leg muscles had no atrophy or fiber changes, indicating “full protection of muscle function,” study co-author Mary Bouxsein, a skeletal researcher at Harvard Medical School, tells Jackie Flynn Mogensen at Scientific American.

The researchers also identified 11 substances in the body, including creatine, lactate and glycerol, that seem to go through changes depending on gravity and could be used to monitor astronauts’ muscles during spaceflight.

Se-Jin Lee, a geneticist at the University of Connecticut who was not involved in the study, tells Scientific American that the results clearly show how different levels of gravity impact muscle structure and function. However, “a key question will be the extent to which these findings will translate to humans during space travel, specifically with respect to the threshold for seeing significant effects on muscle health in humans,” he adds. People and mice are quite distinct in how we use our limbs and in our muscle compositions, among other differences.

Still, the findings provide an important foundation for future work on the effects of gravity on muscle health. “You have to start somewhere, and this is an exciting development,” says Lori Ploutz-Snyder, a kinesiologist at the University of Michigan who was not involved in the research, in an email to Ellyn Lapointe at Gizmodo.

She adds that understanding the gravity threshold for humans would help determine the best artificial gravity levels for long spaceflights, and whether exercise countermeasures to prevent astronaut muscle weakening in microgravity could be scaled back.  

With NASA hoping to send people to Mars and establish a human presence on the moon through its Artemis program, scientists need to know how to mitigate the negative health impacts of space.

Sara Hashemi | Read More

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.