I wonder if there has been any study regarding the head impact involved with running for long periods of time. I've heard for instance the water-skiing can cause minor brain damage because of the constant bumps in the water. I'm curious because I know that running involves a similar kind of minor - although constant - head impact as your body jumps out of each stride. I have no data to back this up so sorry if I'm just blabbering nonsense.
I would imagine there is a step change somewhere in causing brain damage. I.e., if your brain can withstand a 1.5g impact it can withstand any number of 1.5g impacts, but 2g or 3g impacts lead to cumulative damage.
Then again, I don't know what I'm talking, or where running impacts might fall in that spectrum.
