Not to take anything away from what you're saying 'cos i don't know enough.

What has concerned me recently, was a mate who had an off (off road). He was wearing solid plastic type alpine stars MX boots. Powerful protection. Problem was he snapped both bones in his leg about half way down inside his boot. I have been wondering if the inflexibility of the boot caused that type of break

He was thrown off, spun in the air and came down heavy on his leg. I wonder if a flexible boot may have allowed his leg to flex a bit and so not snap
any views?