Interesting to see that on all the many Hillclimb and Sprint events I have visited this year competitors now have a Hans Device fitted to their helmets.
In essence this helps prevent the first stage of Whiplash - that is the head moving forwards into the chest area.
So does this mean that this first head "movement" in a crash causes the damage/whip effect - I think so.
BTW the Hans Device does not seem to apply to Classic Classes.