Going into space does havoc on the human body.
One of the biggest problems is muscle atrophy. When the body isn't working against the forces of gravity to move, or even stay upright, thereby putting weight on the muscles of the legs and back, those muscles can waste away pretty quickly. To combat this, astronauts in space have to work out for two hours a day to keep their muscles in check.
As you can see in the video below of astronaut Colonel Michael Hopkins training aboard the International Space Station, it's pretty intense. … Read more