The human body is not meant to withstand certain things. Perhaps mage's magical abilities gives them a bit of an advantage, a higher tolerance to what they could endure. You've seen Savanaclaw students go down hard enough to snap their necks yet they bounce back up seconds later. Though, surely there have to be limits. Now seems like one of them. A 'what if' scenario in book 4, where you end up with a broken arm in Octavinelle.