Weightlessness wreaks havoc on a body that has evolved in response to gravity. The face puffs as body fluids float freely. Bone, relieved of its duty to support weight, forgets its purpose and stops manufacturing calcium; tendons and ligaments lose their natural resilience; and the heart, no longer summoned by muscles to pump the blood needed to fight gravity, begins to grow weak. The immune system deteriorates, blood volume drops about 10%, and the taste buds fail. Dehydration becomes a serious concern.
Weightlessness provides none of the opposing forces that bones and muscles need to remain healthy and effective. While the debilitating effects of weightlessness may not affect the astronaut in space, once back on the ground, severe repercussions will be felt.
