Major changes occur in the human body during long space missions. These include gradual loss of muscle and bone, space sickness, and changes related to the heart and lungs.
Such changes can affect astronauts' well-being and efficiency, both in orbit and after their return to Earth.
Many studies have been undertaken in order to learn more about the creeping effects of weightlessness. One of the easiest and cheapest ways of doing this is bed rest studies.
Numerous bed rest studies have been performed during the last 40 years. These have provided important information about how people cope with long periods of inactivity.
Volunteers stay in bed for many weeks, often lying with their head tilted down. With little use of bones or muscles, their bodies behave in similar ways to how they would in space.
Scientists use these studies to test new drugs and other ways of counteracting the effects of weightlessness. Many spin-off instruments and treatments have spread to clinics and helped patients.
Future research on the International Space Station promises even more health benefits. Eventually, this research will also pave the way for humans to travel beyond Earth orbit and explore other worlds.