Pete Conrad exercises on the astronauts' bicycle ergometer in-side the Skylab Workshop. The opportunites to study humans in space are still somewhat limited and can involve only a few subjects, so methods have been devised for simulating some of the physiological effects of spaceflight here on Earth. By immersing humans and animals in water baths for extended periods or by confining them to bed or in plaster casts in a slightly head-down position, many of the same cardiovascular changes that occur in space can be produced on the ground and studied in detail. Using his head. When they are not used to work against the gravity field of Earth, bones tend to deteriorate and muscles tend to atrophy, that is, to shrink or waste away.
Similar problems occur in space.
The limited mobility within the small earlier spacecraft and the lack of appropriate stress, even in the larger Skylab and Salyut space stations, produced a continuous loss of bone and muscle tissue in the astronauts. The loss appears slow enough to enable space missions of from six to twelve months to be undertaken without instituting any preventive or remedial measures. On longer flights however, steps must be taken to pre vent these losses. In-flight exercise was tried on the Skylab and is being used by the cosmonauts aboard Salyut missions, but so far the correct combination of measures to be applied to prevent bone and muscle loss has not been found. The search is continuing in the Space Shuttle missions as well as in laboratories on the ground.