Space exercise. Astronaut Richard M. Linnehan exercises aboard the space shuttle Columbia whilst in orbit. The exercise involves pulling down on the purple straps. Linnehan is anchored to the floor by toe straps because of weightlessness. Exercising muscles is important for astronauts because their weightlessness means that they are otherwise not used much. Muscles which are not used will tend to waste away. A similar process happens in the bones of astronauts who spend a long time in gravity-free environment. Photographed during mission STS-78 (20 June-7 July 1996); this shuttle mission was longer than any previous one.