Even though Astronauts exercise everyday while they're aboard the International Space Station (ISS), they still experience a fairly significant loss of muscle mass. So much so that they require physiotherapy once they return to Earth. However, resear...
https://www.engadget.com/2018/02/08/...t-muscle-loss/
https://www.engadget.com/2018/02/08/...t-muscle-loss/