Sudden Impacts to the Head
The essay as a whole actually isn't about damage to the human body. I'm trying to explore the physics (or really, the violations of physics) behind The Flash. One of the topics I am trying to cover involves getting hit in the head; i.e., he can somehow run at superspeed and withstand the accompanying drag forces, but still has a normal human's capacity to withstand blows to the head.
As silly as this may sound, I'm looking for information similar to what they frequently talk about on Mythbusters: the number of "g's" a human head can withstand for a certain length of time before causing serious injury. It really doesn't matter what causes it, to me. If anything, throwing a rock may actually be the wrong approach; the numbers I crunched last night turned out to be puny.