Why does leg day hurt so much in comparison to working out your arms?

As I'm typing this right now, the mere thought of crossing my legs makes me want to scream and I woke up this morning and nearly crumpled to the ground like a new born birthed giraffe. My arms on occasion hurt from doing my arm circuit, but the turn around time is not nearly as long or as painful as leg day. Why is this?
Why does leg day hurt so much in comparison to working out your arms?
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