One big advantage is that we can run while breathing out of sync with our steps. Four legged running pretty much requires each inhale and exhale to sync with the compression and expansion of the torso with each stride. Humans, on the other hand, can run full speed while taking multiple steps per breath, depending on terrain and fatigue, which gives more options for pacing.

I saw it in a documentary but it was a good while ago so to be honest I can't remember what the exact mechanism was or if it was just a contributing factor over longer distances. I just remember storing it away as little nugget that made sense when presented.

It's very late here and now you have me curious so I'll probably have a dig around in the morning.

Edit: I don't think it's the break thing though. Organ damage is definitely better than death if you're being chased.