Space travel causes a plethora of medical and neurobehavioural problems, including the loss of as much as 25 percent of muscle mass, a loss of bone mass of between one and two percent per month, weakening of the immune system, impairments of cognitive performance, and other effects related to the highly stressful environment of a space vehicle. In Module 4, :envihab scientists will be able to monitor the physiological changes that could occur during long-term missions. This knowledge, in turn, can be applied to what happens to the body under strenuous conditions encountered on Earth.