Just as your leg muscles could deteriorate if you lie on the couch all day, the same can happen to astronauts on the International Space Station (ISS). Despite working practically non-stop, the absence of gravity slowly takes its toll. While the average adult is advised to exercise about 30 minutes a day for several days a week, ISS crew members exercise 90-120 minutes every day to maintain their bone and muscle mass in a healthy condition.

They currently use the CEVIS system, which is a cycle ergometer with vibration isolation and stabilization. It is essentially a stationary bike fixed on one side of the ISS to prevent it from floating away. Astronauts wear heart rate monitors while riding the bike and send the data to Earth so their instructors can analyze it and optimize their training routines.

“We have a computer, so if you like listening to music, you can do that. Or watch a movie,” says astronaut Doug Wheelock.