One of the first pieces of equipment that the space shuttle unloaded at the the International Space Station was a new treadmill.
According to NASA, “Exercise is crucial to the astronauts’ wellbeing. Without gravity, crewmembers lose bone and muscle mass and their cardiovascular system weakens. By exercising on COLBERT and other exercise devices, they can counteract these effects and keep their bodies in condition.” http://science.nasa.gov/headlines/y2009/15jun_running.htm
Space Bones. Scientists hope that what they learn about osteoporsis will help with its treatment on earth.
Download NIH’s guide to Bone Health and Exercise