Question

According to "life without gravity",why can astronauts muscle become weak?

Answer 1

without gravity the muscle has no way to work naturally, it just floats around if you move that muscle, in space you cant lift weights to keep them strong, because like i said everything just floats

Answer 2

Without gravity, your body is not working as it should. In space, you are floating so there's no walking or running to keep your muscles built up so because of this, your muscles become weak.

Hope this helped :)