[LeifCarrotson]

Have you ever been skiing? It's your feet that are running into the earth, and hardly even that - they're skating smoothly over it unless you really mess up. On good mogul run,your head hardly moves off a straight line while your legs and hips adjust to keep your skis moving smoothly. In a similar comparison, walking does not produce head trauma.

[endorphone]

I've been skiing plenty of times. Runs where I'm at a high rate of speed and hitting countless variation changes (not moguls, just normal skiing) and my head is shaking so much that my vision is blurry. Landing a jump at best (when you absorb with your legs) is a 19G+ event. Every minor mistake in absorbing can tenfold increase that. Walking is not a relevant comparison.

We evolved to walk with a limited brain suspension that just wasn't adapted for 100kph wax shoe runs.