The position which you take the kick matters more than the total energy of the kick. Since a needle doesn't take 5 ounces of force to go through your skin. But a pile driver may need more than 5 ounces of force to do the same thing.
When a person is bent over like that, any upward kick will deliver more force to the target, because the weight is pushing the head down into the kick due to gravity. Thus it's like in muay thai where someone controls the head, pulls it down, and then knees it.
A knockout has nothing to do with the chin. It's all about causing the brain to bounce hard enough inside the skull.
https://www.youtube.com/watch?v=6LO4YcwnjkA&feature=player_detailpage
This guy gets kicked by a really weak kick and still gets koed, i can jab much much much harder than that lousy kick.
So how hard is the average chin to ko and how hard is the chin of a high level pro fighter know for having a robust chin?
