system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we swing our arms when we walk?

Does it keep balance or is it just a habit?
gpt
it's a counterbalance.

Your body in fact is constantly fine-tuning your gait for maximum caloric efficiency. Now, you can help it by walking properly with a straight back, but if there's one thing the human body does extremely well it's maximise our efficiency when moving.

Swinging our arms means we can keep going without having to stop every so often to sort out our momentum. It means we're not burning valuable calories using our core muscles to stay upright against the momentum of our own legs.

Pretty neat, huh?