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Muscles and Bones in Space

Muscles and Bones in Space

Astronauts must exercise at least two hours every day while aboard the ISS.
Courtesy of NASA.

  • Grades:
  • Length: 45 Minutes


Students learn how human muscles and bones change during space missions, and devise preventative solutions to help limit those changes.

This activity is from The Science of Muscles and Bones Teacher's Guide, and was designed for students in grades 6–8. Lessons from the guide may be used with other grade levels as deemed appropriate.

Teacher Background

On Earth, muscles and bones are used to working against gravity to maintain posture and balance. In space, where the effects of gravity are almost absent, the muscles and bones of astronauts do not have to work as hard and become weaker. Bone rebuilding falls behind bone dismantling, and bones decrease in diameter and become less dense. The calcium removed from bones is permanently eliminated from the body in urine, leading to a condition similar to osteoporosis on Earth.

Muscles in space also become smaller and weaker through a process called atrophy. In addition, the fibers inside muscles change because most work in space involves short-duration, high intensity tasks.

The adaptation of muscles and bones to microgravity conditions does not have serious consequences in space, where astronauts do not need as much strength to keep their balance and move about. In fact, the bodies of people in space eventually reach equilibrium, called “space normal,” with their new environment. This adaptation does, however, cause problems when astronauts return to an environment with the full force of gravity because their muscles and bones have become too weak to function as before.

Similar problems can be observed on Earth among people who are bedridden during a long illness, who have part of their bodies immobilized to allow a fracture to heal or who suffer from osteoporosis. Research to develop measures that will counter changes in muscles and bones in space will benefit these and many other people directly.

Objectives and Standards


  • Using resources to gather information

  • Applying knowledge

  • Drawing conclusions

  • Presenting conclusions with supporting information

Science, Health and Math Skills

  • Lack of stress causes bones and muscles to become weak.

  • Astronauts must counteract the effects of lost stress on bones and muscles.

Materials and Setup

Materials per Student

  • Copy of the student page


Provide resources on space topics.

Procedure and Extensions

  1. Review the concepts presented in this unit. Discuss how lack of stress affects bones and muscles. Ask students to think of environments in which stress on the body is reduced, such as when on the space shuttle or space station, or during bed rest.

  2. Hand out the student sheet and have each student complete it alone.

  3. Have students share their drawings with the rest of the class.

Related Content


National Space Biomedical Research Institute

National Space Biomedical Research Institute

This work was supported by National Space Biomedical Research Institute through NASA cooperative agreement NCC 9-58.