Why have scientists developed exercises for astronauts living in outer space for long periods of time?

Question

Why have scientists developed exercises for astronauts living in outer space for long periods of time?

Answer 1

If they didn't exercise ,there bodies would dump so much calcium  that it would be dangerous for them to come back to gravity...

Answer 2

Here on Earth you have gravity pushing down on you, as such whenever you pick things up, your muscles have to fight against gravity to keep it up, likewise when walking, or even just standing up, your legs are working to keep you upright and stable.

In space, orbiting the Earth, you're in microgravity, which means very little force is required to pick anything up, or propel yourself along. All that's needed is a gentle push to move yourself along.

Not using your muscles for an extended period of time will lead to muscle atrophy, which is where your muscles lose mass and become quite weak. That's not really a problem in space, but when you come down again it really is, because you won't be able to stand up or lift things.

Take a read:

http://en.wikipedia.org/wiki/Atrophy

Answer 3

You use your muscles daily by doing normal things. A walk down the hallway expends energy,keeps your muscles toned, and your bones rigid & calcified.  

Long term weightlessness, besides being kinda fun, removes the body's "fight" with gravity.  You now spend much *less* energy moving from place to place, and without the need for the muscle & bone, the body reacts by not replacing muscle & bone tissue that is lost.  The result is, atrophied muscles, and bone loss.  Exercises keep your muscles toned, and the stress encourages your body to replace lost tissue.