Muscles that are not used get smaller and weaker. This process is called muscle atrophy(28.8K) (56.7K) (download). It is so easy to move around in orbit that astronauts do not make as much use of the muscles they normally use on Earth.

This situation results in muscle atrophy. To help prevent muscle atrophy, astronauts exercise on specially designed exercise equipment during orbit. (28.8K) (56.7K) (download) People on Earth sometimes experience muscle atrophy. To find out what it is like, interview someone who wore a cast, someone who was hospitalized for at least 2 weeks, or a doctor.