If you play a sport, you know that staying in shape in the off-season is just as important as it is during the regular season. If you do not keep up your training during the months you are off, you will lose your strength and agility.

Just like athletes everywhere, astronauts have to keep in shape both on Earth and in space. Due to the lack of gravity in space, astronauts experience a decrease in muscle mass and bone density. Without having to work against the force of gravity to support ourselves, our bones and muscles begin to weaken and deteriorate while in space. In fact, after just six months in space, an astronaut can lose up to 10 percent of his or her bone mass. That same mass can take up to four years to build back up on Earth.

To fight against this deterioration, astronauts have a very vigorous exercise regimen in space. They must do at least two hours of exercise every day. Thanks to this intense exercise regimen some astronauts return to Earth in even better shape than when they left!

Watch NASA astronaut Randy “Komrade” Bresnik explain the different types of workout equipment and the exercises astronauts use in space. Then, learn how you can create an experiment to simulate the effects of bone loss at home with the help of the STEM in 30 team!


In this episode of ISS Science Astronaut Randy Bresnik explains why exercising in space is so important. Also learn about bone density in a hands-on classroom activity using cereal.

Subject: Life Science | Grade Level: 2-5 | Time: 45-60 Minutes

Lesson Plan: Bone Density Loss

Related Topics Spaceflight Human spaceflight Space stations
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