Astronaut Sunita Williams uses the treadmill onboard the ISS in 2012. The harness is visible reaching from the treadmill’s base to a ring on her hip.
| Photo Credit: NASA
Are you trying to lose weight? Because in space you are already weightless. However, it is interesting to think about how astronauts can exercise in space, which they need to do to keep from losing muscle mass.
Work is defined by a force displacing an object by some distance. When you lift a 5-kg dumbbell on the earth, you work to move it through the air. The amount of work depends on the amount of force exerted in this activity.
On the ground, you work to overcome the downward force the dumbbell exerts on your hand, called its weight, and to move the dumbbell up. If you’re onboard the International Space Station (ISS) in low-earth orbit, both components almost completely vanish and you do very little work to move the dumbbell up and down.
Similarly, unlike walking on the earth, where you work to overcome your own weight and friction against the air and the ground, in space the former is very small and the latter is zero. (In low-earth orbit, astronauts experience microgravity, not zero gravity.)
To exercise onboard the ISS, astronauts use a special weight-lifting machine called the Advanced Resistive Exercise Device. An astronaut uses their hands and shoulders to push against resistance provided by air-filled pistons, which can simulate a weight of up to 270 kg.
Similarly, the ISS has a treadmill where astronauts can strap themselves down using a harness: the tighter it is, the closer the force it exerts will be to gravity.
Published – March 25, 2025 03:00 pm IST