Astronaut physiology

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Astronaut: a man or woman whose job it is to fly in space. Astronauts are usually really good at math and science, and aren't scared of sitting on top of rockets.

Mega Muscles?

Astronauts exercise on special treadmills using bungie chords to help keep their muscles strong on long trips into space.

Astronauts exercise on special treadmills using bungee cords to help keep their muscles strong on long trips into space.

You might think an astronaut’s muscles get bigger while in space, since they can hold up a co-worker with one finger. But what looks like super strength is actually due to the weightlessness that occurs without gravity. Because everything floats, muscles don’t have to work as hard. While this might be fun at first, when muscles don’t have to work, they shrink.

Without exercise, astronauts in space get weaker and weaker. Their legs get thinner from muscle loss until they get what are called “chicken legs.” If they stay in space long enough and their muscles get weak enough, they won’t be able to stand up when they get back to Earth.

Blood movement and muscles aren’t the only things that are affected by living in space. Bones become weaker when they aren’t used a lot, and our sense of balance gets a little wacky too.

Additional images via Wikimedia Commons. Biceps picture by OpenStax College.

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Bibliographic details:

  • Article: Mega Muscles
  • Author(s): Amy Shira Teitel
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: December 8, 2011
  • Date accessed: May 15, 2024
  • Link:

APA Style

Amy Shira Teitel. (2011, December 08). Mega Muscles. ASU - Ask A Biologist. Retrieved May 15, 2024 from

American Psychological Association. For more info, see

Chicago Manual of Style

Amy Shira Teitel. "Mega Muscles". ASU - Ask A Biologist. 08 December, 2011.

MLA 2017 Style

Amy Shira Teitel. "Mega Muscles". ASU - Ask A Biologist. 08 Dec 2011. ASU - Ask A Biologist, Web. 15 May 2024.

Modern Language Association, 7th Ed. For more info, see

Muscles have less work to do in space so keeping them strong takes extra work.

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