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Your Body in Space: Use It or Lose It
Female astronaut exercising surrounded by machinery
Besides eating and sleeping, what do astronauts spend more time doing in space than anything else? It's exercise.

Image to right: Astronaut Peggy A. Whitson exercises on the Space Station in 2002. Credit: NASA

Exercise is the number one health priority in space, said Don Hagan, director of exercise physiology at Johnson Space Center. "No other activity except eating and sleeping is given that much priority. Two and a half hours each day are devoted to fitness."

Why is it so important for astronauts to exercise while they're in space? If astronauts don't exercise, their bodies start losing bone and muscle. Bone and muscle loss mean decreased size and strength, and can reduce an astronaut's ability to do work because it makes them weak.

Weakened astronauts would be less able to do tasks while in space, Hagan says. Also, if there were an emergency, the astronauts would need to be in good shape to get out of the Space Shuttle or Space Station quickly. Once they land on Earth, weakened muscles and bones would make walking difficult.
Male astronaut exercising with portable CD player and headphones
Muscle can be built back up with therapy. But lost bone is not as easy to get back.

Image to left: Astronaut Robert L. Curbeam works out on the ergometer on the Space Shuttle Atlantis in 2001.
Credit: NASA

In microgravity, body fluids are moved around. Fluids such as plasma are lost throughout the body. Plasma is where red blood cells live. Less plasma means there is less blood to carry oxygen to the rest of the body. Exercise, however, has been shown to increase the amount of plasma in the body. Astronauts who exercise make more red blood cells.

Microgravity also brings about another change in something called "orthostatic intolerance," Hagan said. "When you lie down, stand up quickly, and feel light-headed, that's orthostatic intolerance," he said. "Your body tries to stop this from happening. It does so by increasing its heart rate and blood pressure to keep more blood returning to your heart. If you can't do that, you'll pass out. With no gravity and less blood volume, astronauts are more prone to fainting. Again, exercise can help increase blood volume and circulation. That helps prevent fainting.

Three Main Exercises

In space, astronauts use three pieces of exercise equipment. Each piece does something different. The exercise equipment is put on raised platforms to reduce the noise the machines make.
  1. Cycle Ergometer: This is like a bicycle, and the main activity is pedaling. It is used to measure fitness in space because it's easy to check heart rate and how much work is being done.
    Male astronaut exercising with harness on shoulders.

    Image to right: Astronaut Ed Lu uses the RED equipment on the Space Station in 2003. Credit: NASA

  2. Treadmill: Walking or jogging on the treadmill is like walking on Earth. Walking is the single most important way to keep bones and muscles healthy. Because the lack of gravity tends to make people float, harnesses are attached to the astronauts to hold them to the walking surface.

  3. Resistance Exercise Device (RED): The RED looks like weight-lifting machines you may see on television. To use it, astronauts pull and twist stretchy rubber-band-like cords attached to pulleys. The RED can be used for a total body workout. From squats and bending exercises for the legs, to arm exercises and heel raises, astronauts can do them all on the RED.
Russians and Americans have different exercise routines on the Space Station. But they all have the same goal: keeping the astronauts and cosmonauts healthy.
Adapted from Use It Or Lose It