Bed rest studies provide an opportunity to conduct ground-based studies of the physiological changes which occur on orbit. Astronauts are known to lose muscle and bone mass during space flights, and effective countermeasures are being sought. The muscle loss is extensive, even for short duration missions, but it is fairly easily regained upon return to the earth’s gravity. Bone loss, on the other hand, is a slower process. The effects are long lasting, and significant loss from a long duration mission may cause fracture when the body is subjected to the sometimes rigorous forces of gravitational environments. For this reason, studies are being done at NASA’s Johnson Space Center Bone and Mineral Physiology Laboratory on heavy resistive exercises that decrease or prevent loss of bone mineral density (BMD) in bed rest subjects.

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