On a Trip to Mars, Astronauts’ Muscles Could Waste Away

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They have treadmills and exercise bikes, but astronauts do not maintain muscle mass during long space voyages — a finding that suggests big problems on manned missions to other planets.

In the first-ever cellular analysis of astronaut muscles, nine members of the International Space Station crew offered up muscle biopsy samples from their calves. The crew gave one set of samples roughly 45 days before flight, and a second set on the day of their landing, after about six months in space. Researchers already knew that low gravity was bad for astronauts’ muscles — particularly for the legs, which support far lower loads in space than back in normal gravity on earth. But this is the first time that loss of muscle mass and function could be measured in cell tissue. The results weren’t pretty.

Muscle loss did vary with the amount of exercise done on board the space station — but all of the crew members had at least some loss of muscle function. Writing in the Journal of Physiology, the researchers, led by Robert Fitts of Wisconsin’s Marquette University, report that the astronaut with the least amount of damage showed no atrophy at all in one of the main calf muscles. But the astronaut still had “a modest 10% loss in fibre force.” Meanwhile, however, another astronaut lost fully 51% of fibre size and 70% of muscle force during the same study period.

The authors write:

An obvious conclusion is that the exercise countermeasures employed were incapable of providing the high-intensity needed to adequately protect fibre and muscle mass, and that the crew’s ability to perform strenuous exercise might be seriously compromised.

And this was after just six months in space. On a trip to Mars, for example, roughly 10 months away, astronauts might have trouble conducting even normal work on the planet’s surface, the study authors suggest. Astronauts might also lack the strength to make an emergency landing if needed (for example, when they come home). More high-resistance muscle training may be part of the answer, the researchers say.

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