HOUSTON -- Astronaut Michael Barratt spent more than six months on the International Space Station, making him well qualified for his current job as manager of NASA's Human Research Program, studying the effects of space on the human body.

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CBS News correspondent Chip Reid looks at the Johnson Space Centers Neutral Buoyancy Lab, a pool with an underwater mock-up of the International...

Barratt, a medical doctor, says a more serious problem is that months of zero gravity can leave bones brittle and muscles weak. Fortunately, there's a simple solution: vigorous exercise that offsets the loss of muscle and bone mass.

Tom Marshburn

CBS News

"When I finished my five-month mission, I was able to stand up, walk a straight line, and it's quite an accomplishment," Marshburn says. "We had not been able to do that before."

When not in space, Marshburn works on the strength and dexterity needed for space walks in a giant pool at the Johnson Space Center in Houston. But some effects of space on the human body don't have simple answers.

"It's safe to say that radiation is our biggest concern," Barratt says. "Unfortunately, the space flight environment is a radiation environment."

Astronauts train in a giant pool at the Johnson Space Center in Houston.

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How astronauts combat debilitating effects of space