Background Fact: Older individuals are sometimes less physically active than younger individuals, which makes older individuals more at risk for osteoporosis. Interestingly, this is the same phenomenon that makes astronauts at risk for osteoporosis if spending long periods in space. Space Shuttle Endeavour on Pad39A

Brainteaser: Try to reason out a feedback loop that could explain how a decrease in physical activity could worsen osteoporosis.

Take some time to consider the above scenario.  Think in particular about what cell types might be responsible for creating the condition of osteoporosis in this situation.  You're welcome to look for some answers online to explain this, but don't spend more than a few minutes doing so!

Once you have taken some time to think and find information, submit a few sentences here to record your thoughts.  You might discuss your ideas about what interactions among cells serve to create weak bones after a lack of physical activity, or just talk about what you find confusing/questions you have!