system
Given the following post, respond as if you're commenting on Reddit:
human
Why is the brain not damaged by impact from running, how is it protected from this sort of impact but not from other impacts?
gpt
Your ankle joints, knee joints, and to some extent your neck joints all act as shock absorbers. Because of this, your head doesn't bob up and down as harshly as your feet do. 


If you were to run with a cup of water and try not to spill it, you could probably do it. You'd accommodate for the impacts with your different muscles to stabilize it so it moved less. You're doing that with your head without having to consciously try.