Train Astronaut Exercise: Today's Fitness Play of the Day

Jan 05, 2021

Did you know it is important for astronauts to still exercise while they are in space? In fact, exercise for astronauts is in many ways is more important than exercise on Earth. In today’s Fitness Play of the Day from the Ripken Playbook, you will learn about the importance of bone health while exploring what it means to stay fit as an astronaut in space.

What is Microgravity?
Check out this video from the International Space Station to learn about the effects of microgravity on the body in space. Check out this link for more information about today's activity!


  • Bone Density Student Activity Worksheet (pages 4 – 5) *hyperlink*
  • 4 plastic baggies
  • Cereal, coins, M&Ms, etc. (or anything of similar sort and size)
  • Heavy book
  • Permanent marker
  • Student worksheet *hyperlink*

The loss of bone and muscle mass, variation in behavior, and body-wide alterations initiated by a changing nervous system are some of the most apparent and potentially detrimental effects of microgravity. Loss of bone mass is particularly noticeable because it affects an astronaut’s ability to move and walk in space and return to Earth’s gravity. Astronauts spend much of their days “floating” and propelling themselves with their arms, which eliminates the need for bones, as they are used in standing and walking on Earth.

For these reasons, exercise is an imperative part of any astronaut’s daily routine. It slows the rate of reduction of bone mass, and keeps the crew healthy and ready for any physical challenge they may face in space. 

Let’s Begin
Explore the effects of depleted bone density in this fun activity! In this activity, baggies will be used to represent bones and cereal to represent bone density. The more cereal in a baggie, the higher the bone density, and vice versa.

  1. Use a permanent marker and label the bags 1-4. 
  2. Fill each bag with pieces of cereal. 
  3. Bag 1 represents healthy bones on Earth – this will be the “densest” bag and therefore will contain the most pieces of cereal. Fill Bag 1 with as many pieces as you can and keep count of the number of pieces in this bag.
    1. Make sure the bag is closed tightly
  4. Fill the remaining 3 bags, each with fewer pieces of cereal than the first bag (remember to keep count). Fill each bag according to the following:
    1. Bag 1: 0% bone loss (normal bone) 
    2. Bag 2: 80% of original bone remains; 20% bone loss 
    3. Bag 3: 60% of original bone remains; 40% bone loss 
    4. Bag 4: 40% of original bone remains; 60% bone loss
  5. To determine the amount of cereal needed in Bag 2, you will need to calculate 80% of normal bone density. To do this, you will multiply the number of pieces of cereal in Bag 1 by 0.8 to find the total number of pieces you should put in Bag 2.
  6. Use the same method to calculate 60% and 40% of the normal bone density, and fill Bag 3 and Bag 4 with these amounts. Be sure to record data on your worksheet.
  7. Now it is time to see what happens when a bone is exposed to a sudden force. Place Bag 1 on a hard surface. Place a heavy book on top of the bag and push down with a hard force. Repeat this step with Bags 2-4.
  8. What happened to your bones? Count the number of unaffected cereal pieces in each bag. Be sure to record your data on your worksheet. 
  9. How much bone was unaffected? To calculate this, use the formula below, and record your values on your worksheet (# unaffected remaining in the bag / original density of the bag) x 100.
  10. How much bone was damaged/affected? To calculate this value, subtract the unaffected bone percentage from 100%. Record your data on your worksheet.

Check out more fitness activities in our Healthy Choices, Healthy Children -- Fitness edition