Originally Posted by
FBinNY
It really depends on how you fall. If falling sideways it doesn't matter what your forward speed is, except for torsional and road rash considerations.
Consider a bouncing ball. Drop the ball and it rebounds to a certain height. Throw it sideways and when it falls to the ground it'll rebound to the same height as the dropped ball. The forward speed is unaffected by the impact, except that some spin will be imparted.
However, if you go over the bars, hit a wall or car, or are hit from behind, then forward speed comes into play since the impact will be changing that.
In all cases what matters is the change in speed and direction, not the speed itself.
In the first place, torsional considerations are crucial. Rotating the head (extremely likely if it strikes the ground at an oblique angle at high speed) bounces the brain around inside the skull and gives rise to diffuse axonal injury to the brain, which is highly damaging.
In the second place, the bouncing ball doesn't have my brain inside it. As my head rebounds from the ground, my brain decelerates rapidly as it crunchesninto the inside of my skull.
I agree with your other points. But really, to suggest that the speed at which my head impacts the ground is immaterial to my rosk of injury (which is waht was suggested in the post to which I replied) is absurd.