As requested... though I'm an interfacial scientist rather than just your standard run of the mill materials scientist Thank You Very Much.
I invite you,
@young Ed, (ha! I can even say that and not sound patronising, for a change!
) to compare the relative hardness of two small bits of plastic to that of bone. From the clip, it is obvious that his back took the brunt of the fall rather than his helmet or head. No broken spine, no broken ribs, no pneumothorax. And his back didn't even have a helmet! I've done rather similar to myself in the past, without ill effects or brain damage [1] - all without the benefit of a helmet. Your skull is tougher than most people realise, thanks to half a billion years of evolution. Your neck, though, is not. It, as a structure, has only been around to support a heavy head for less than a million years. It does not seem wise to transfer impact loads from a strong skull to weak neck vertebrata.
[1] Others may disagree on this issue
