system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: how does it work that for every pound of weight you lose, there is a 4 pound stress reduction in your knees?
gpt
Place a rock on your foot. That's how much it weighs. Now drop the rock on your foot. Different experience?

Walking or especially running requires your knees to not just support your body weight but stopping your falling body weight.