I have done lots of martial arts in my day. The other day I got into a conversation about punching technique. My point to them was that for a punch to hurt it's all about the snap back; try to pull back twice as fast as you came in.
But when I was thinking about the scientific reason for this, we (3 engineers) were not in agreement, and not really understanding why.
If you do a follow through punch, then your kinetic energy is transfered into deformation of the person's body, then into kinetic energy of their body moving.
However, if you did the snap back technique, the main question of dispute was if this was analogous to why whipping someone with a wet towel hurt, or wheather it was more to do with how nerves work (a sustained deformation hurts less?).
happy hump day.