Q&A: How Astronauts Exercise

Question: My science teacher showed us a video of astronauts floating around in the ISS [International Space Station] and it made me wonder if they even bother to exercise. I mean, it looks like everything is so easy for them. Almost like their whole day is in slow motion. — WW, Portland, OR

Answer: They more than “bother to exercise,” they have to exercise or several bad things happen to them. The two most critical changes are bone de-calcification (bones lose their strength) and muscle atrophy (muscles lose mass and get weaker) — and that includes the heart muscle. There are other changes, but these are the two most important. Most of these changes are related to being weightless, but some are due to the higher radiation levels in space, or physical stresses during launch and reentry.

The video shows how some types of exercise just don’t work in microgravity (NASA’s official term for weightlessness). Any exercise that relies on gravity, like pushups, chin-ups, sit-ups, or anything involving lifting free weights like squats, and bench presses, just won’t provide any benefit to the body — save for a moderate aerobic workout.

But resistance exercises, like pushing or pulling elastic- or spring-based mechanisms, requires the muscles to do real work. You see many examples of that in the video. Elastic straps are also used to hold astronauts to treadmills for aerobic benefits, and to rowing or cycling machines for both aerobic and strength training.

With ISS missions lasting for months, exercise is required to avoid adverse changes to the body. Two hours each day are dedicated to exercise. Despite all this training, when astronauts return to Earth they always feel weaker than before they left.

Trips to the Moon are less a problem, since missions are measured in days or weeks. And once on the lunar surface they do experience gravity, albeit only 1/6 that of Earth. For trips to Mars we’re talking about missions that could last for years and would absolutely require an exercise regimen. Even with artificial gravity.

If you’re curious about how astronauts weigh themselves (which they’re also required to do on a regular basis) take a look at my post: How Astronauts Measure Their Weight.

Next Week in Sky Lights ⇒ How Astronauts Sleep

Mammatus Clouds
Q&A: How Astronauts Sleep