system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the back usually hurt after standing up for a certain amount of time, but not after walking the same amount?

Edit: after standing up still*
gpt
Standing in place is actually way harder for your body. The muscles in your lower back are always tense when you stand. Where as when walking, they get relaxed and then tense up again.
Imagine doing 20 pushups in 5 minutes. Now imagine doing 1 pushup in 5 minutes (staying low)