Because the body does not have to fight against gravity in space, there is a serious danger of it losing bone and muscle mass. Astronauts must exercise every day to prevent their muscles wasting away. In the ISS there is a treadmill and a stationary exercise bike, but astronauts must remember to strap themselves on or they will float away.
Exercise is an important part of the daily routine for astronauts aboard the station to prevent bone and muscle loss. On average, astronauts exercise two hours per day. The equipment they use is different than what we use on Earth. Lifting 200 pounds on Earth may be a lot of work. But lifting that same object in space would be much easier. Because of microgravity, it would weigh much less than 200 pounds there. That means exercise equipment needs to be specially designed for use in space so astronauts will receive the workout needed.
The environment of the International Space Station isn’t exactly hospitable to the human body. Thanks to microgravity, astronauts experience a variety of health and physical changes while living in space — some of which they can counteract through daily exercise and other activities. But the space environment also exposes astronauts to other elements that cannot necessarily be mitigated.
Our bodies aren’t built for space; they’re built for a planet a lot like our own. Human beings have evolved here on Earth over millennia, so our bodies have adapted to excel in a gravity environment under the protection of our planet’s atmosphere. In low Earth orbit, however, those ubiquitous elements are taken away, and the body’s various systems adapt accordingly.
Perhaps the biggest change astronauts experience is bone and muscle loss. Humans on Earth work out these systems every day, simply by moving and standing against gravity. But without gravity to work against, the bones lose mineral density and the muscles risk atrophying. It’s something astronauts are consistently trying to prevent from happening. “We try to minimize it as much as possible,” says Bob Tweedy, the countermeasures systems instructor at NASA’s Johnson Space Center. To do that, astronauts on the station work out six out of seven days a week for 2.5 hours each day.
The International Space Station is equipped with three machines designed to give astronauts that full-body workout: a bicycle, a treadmill, and a weightlifting machine called ARED, for Advanced Resistive Exercise Device. Each machine is specially designed for space, since normal gym equipment would be useless in microgravity. Lifting weights, for instance, wouldn’t do much in space since dumbbells wouldn’t weigh anything. So instead, the ARED machine utilizes two canisters that create small vacuums that astronauts can pull against with a long bar. This allows them to do squats, bench presses, dead lifts, and more.
Similarly, the station’s treadmill is no ordinary running machine. Astronauts have to be strapped into it with a harness and bungee chords, otherwise they would float away and never actually get a workout. A stationary bicycle is also available for strengthening astronauts’ legs, though it has no seat (since your butt wouldn’t sit on it anyway). Instead, astronauts grip handles and sit up against a back pad to stay stationary. Practicing with this equipment on Earth, it’s hard to get a full grasp of what they will feel like in space, since gravity is ever present.