[suzzer99]

This seems like a real problem for older astronauts who will never be able to gain that muscle back.

Muscle mass is so vital for long term health. 70-year-olds confined to bed rest for just two weeks have been observed to lose significant muscle mass that they most likely will never get back.

Obviously most astronauts are younger than 70. But they're also losing a lot more muscle mass and bone density.

[inglor_cz]

Progress in stem cell treatments might be able to treat that muscle mass loss. We are getting closer to regenerating tissues at will, although obviously the main effort is concentrated on the cardiovascular system and nerves.

[voldacar]

You could just give the 70 year olds testosterone replacement and they would gain it back and more, probably