While in space, the bones and muscles of astronauts undergo adverse physiological changes as a result of microgravity (weightlessness). Muscles atrophy while bones lose mass causing them to become brittle. Because of these changes, astronauts oftentimes have difficulty readjusting to life on Earth. Muscle atrophy can be prevented with some success using unique exercise equipment that utilizes harnesses, springs, elastic cords, or vacuum pumps. However, bone loss remains a major hindrance to manned, long-duration missions in space. When future astronauts step onto the surface of Mars for the first time afte a six-month weightless journey from Earth, they will need strong bones. Recently, NASA-funded scientists may have found a solution. By standing on a lightly vibrating plate for 10 to 20 minutes each day, and held down with the aid of elastic straps, astronauts may be able to keep their bones healthy. Understanding how Earth life reacts to conditions in space or on other planets is one of astrobiology's primary goals. Researchers also believe that the same therapy could be used to treat some of the millions of people who suffer from a form of bone loss, called osteoporosis here on Earth.