Why can astronauts' muscles become weak?

Astronauts' muscles can become weak due to the microgravity environment of space, which reduces the need for muscle strength and use. In space, the body does not have to work against gravity, leading to muscle atrophy and loss of strength over time. Additionally, the lack of resistance and weight-bearing activities further contributes to the weakening of muscles. To mitigate this, astronauts engage in regular exercise routines while on missions to maintain muscle mass and strength.