Living in Space 
Flying in space is a risky business. Rockets are dangerous, there's no air, and radiation is a constant threat. And then there's the problem with fingernails....
The human body doesn't seem to like flying in space. In the microgravity environment of Earth orbit, muscles don't have to work as hard as they do on the surface. So under the principle of "use it or lose it," astronauts lose muscle mass. But they can minimize the loss with exercise. In fact, astronauts aboard the International Space Station spend up to two hours a day doing aerobic or resistance training.
In addition to muscle density, astronauts also lose bone density, especially in the lower half of the body -- about one and a half percent for every month in orbit. So an astronaut who spends six months on the space station comes back with bones that have lost about a tenth of their thickness -- something that would take decades here on Earth. Exercise doesn't help -- and neither does anything else. And scientists are still debating the cause of the problem.
The fingernail problem is a little easier to understand. About one-tenth of spacewalkers suffer damage to their fingernails -- including losing the nails entirely. Some even have their nails removed before traveling into space. The problem is their gloves. They're extremely tight and stiff, so they cut off circulation.
That problem could be fixed with a new type of spacesuit. More about that tomorrow.
Script by Damond Benningfield, Copyright 2010