Drugs to prevent motion sickness can provide some relief for the symptoms of space adaptation syndrome, and the condition generally passes in a few days. After a few days in space, the vestibular system disregards all directional signals. Soon after an astronaut returns to the earth, the organs of balance resume normal operation. Over a period of days or weeks, an astronaut's body experiences deconditioning . Strenuous exercise helps prevent deconditioning.
Space travelers ride exercise bikes, use treadmills, and perform other types of physical activity.
After many months in space, a process called demineralization weakens the bones. Most physicians believe that demineralization results from the absence of stress on the bones in a weightless environment. The experiences of Soviet cosmonauts who spent long periods in orbit showed that vigorous exercise and a special diet can minimize demineralization. In addition, astronauts can carry portable life-support systems in backpacks when they work outside the main spacecraft. A manned spacecraft must have a source of oxygen for the crew to breathe and a means of removing carbon dioxide, which the crew exhales.