Fred Bowen The Washington Post

Being in a weightless environment can cause muscles to grow weak and bones to become more brittle. Weightlessness is also hard on the heart because with little gravity the heart does not have to work as hard to pump blood to all parts of the body.

Being in a weightless environment can cause muscles to grow weak and bones to become more brittle. Weightlessness is also hard on the heart because with little gravity the heart does not have to work as hard to pump blood to all parts of the body.