The Problem Astronauts are traveling to Mars in 2024. There are a lot of problems and one of them is muscle atrophy. Muscular atrophy is the loss of muscle tissue due to disease or lack of use. It is a problem in space because humans don't use that much muscle up in space and that causes muscle atrophy. They can't use that much muscle up in space because there is no gravity and they are not working against gravity.