Every time I grind the boards, my first reaction is to lift my foot. Probably a bad reaction, but it is instinctive. The board pushes up on my foot. Of course, I have never ground them that hard. I usually straighten up and slow down (get off the throttle, touch the back brakes) when I first hear them grinding.
I do have floorboard extensions, so they probably grind a lot sooner than that guy's did.