The need for an astronaut to keep fit while in space has been known for years. Before space travel even began, scientists voiced concern about the effects of microgravity on the human body. This became a real concern as studies of astronauts who spent a long time in space revealed a number of issues. These included loss of bone mineral density and general muscle atrophy. Astronauts exercise vigorously to prevent these problems.
The National Aeronautics and Space Administration (NASA) has found through research that exposure to microgravity causes astronauts to lose bone calcium. This is because very low gravity interferes with the body's bone maintenance processes. If you were an astronaut in space and not subjected to gravity, your body wouldn't need to maintain bone to support its weight. That's because you'd need very little of it in such an environment. On Earth you need bones to support your weight.
NASA research has found that astronauts can lose 1 to 2 per cent of bone mass per month. This is due to a condition known as atrophy. Unlike on Earth, humans don't remain anchored to the floor on a space shuttle or at the International Space Station. They float about weightless. Unfortunately, scientists don't know as yet whether the bone loss stays steady or if it levels off or stops after some time.
To prevent bone loss that develops in a microgravity environment, astronauts need to exercise. Astronauts at the space station use three different types of exercise equipment. This includes special treadmills and mechanical bicycles as well as a weight machine that simulates gravity. Together all the equipment is known as the Resistance Exercise Device (RED) system. For the treadmill, an astronaut must wear a harness that tethers him to it while he runs.
NASA has determined that using a special stationary bike can also help to prevent the loss of bone. The specially-designed bike bolts to the floor of the space station. To use it, astronauts sit down and fasten themselves to the seat with a belt. Next, they strap their feet into the bike's pedals. Additionally, astronauts train on a weight machine that allows them to lift weight as if they were on Earth.
Even when astronauts in space exercise regularly, NASA finds they still suffer from a tiny amount of bone density loss. This will pose a problem if humans hope to travel to Mars and other planets. That's because such space travel will take months or years. NASA is working on this issue and experimenting with adding other equipment to the treadmills, bicycles and weight machines that astronauts use.