system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do you hold your arms up while you run but hold them at your sides when you walk?
gpt
Holding your arms up when running makes it easier for your arms to keep pace with your stride because you are swinging a pendulum the length of your shoulder-to-elbow instead of swinging a pendulum the length of your shoulder-to-fingertips.