"Head down bed rest is a good way to mimic a person travelling in space without gravity," Nasa said.
Head-down bed rest helps researchers study people on earth in a way that causes some of the changes the body goes through while travelling in space without gravity.
"This study will show how much your body, tilted down slightly with head down and feet up, for 70 days, 24-hours a day, without getting out of bed, except for limited times for specific tests, is like an astronaut's body during the weightlessness of space flight, Nasa said.
Watching the participants, the scientists hope to learn how an astronaut's body will change in weightlessness during space flight in the future.
The selected participants - divided in exercising and non-exercising groups - would be free to move around inside the bed rest facility for two to three weeks and do normal things.
After that period, they would spend 70 days lying in bed, with your body slightly tilted downward (head down, feet up). During the final 14 days of the study, they would again be free to move about within the facility.
Because of deconditioning that takes place during bed rest, they would slowly begin normal, everyday activity.
"You will participate in the reconditioning activities that are arranged for you during this time," Nasa said.
Nasa is looking for healthy US citizens or residents, who will have to pass tough fitness tests, as they have to be of similar physical condition to an astronaut.
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