Everything

Assume that a running body that exceeds its normal maximum velocity suffers physical stress at one-and-a-half times that speed, and starts taking damage at twice that speed. That “maximum velocity” thing is pretty subjective when it comes to living beings, but assume that a living (or undead) thing who’s moving at twice its maximum running speed is starting to hurt.

Each success above the second one inflicts one lethal health level, per turn, on the poor critter unless that critter has been “enhanced” with Life 3 or 4 beforehand. (Life 3 if the mage is enhancing himself, Life 4 if he’s enhancing someone else.) This strain applies only to creatures who are moving under their own power – running, swimming, flying or whatever past their normal capacity. A spell that picks someone up and flies her down the street at 100 MPH won’t inflict that kind of stress on her, although hitting something at 100 MPH will probably rather suck – see below.

With regards to that Life-Sphere enhancement, the usual mixed-Sphere rules apply to vampires, werewolves and so forth. Note that vampires with the Celerity Discipline, or werewolves who are using Rage to move faster, are not affected by this damage, as they’re already sort of “built for speed” and can tough it out.