Doctors on the ground monitor the fitness of the crew and work out how much their condition has changed. They can instruct the crew to alter their exercise programmes, if required. There are several exercise machines on board the ISS that are used by the astronauts. They include two treadmills, a resistive exercise device, and a cycling machine (ergometer). In each case, the astronauts have to be attached to the machine so that they don’t float away!

The treadmills are used to simulate walking and running in normal gravity. The cycle can be used to exercise arms or legs. The resistive exercise device is rather like weightlifting on Earth. It allows the user to complete a series of physical exercises while restrained by elastic bungee cords. A portable computer monitors heart rate and other vital signs while the astronauts are using the machines.