If action equals reaction, how is it ever possible to win in martial arts?

Question

In kick-boxing, when a fighter's leg hits an opponents leg, the outcome, based on Newton's 3rd law, should be the same for each fighter. It's not even important who kicked who, as in the moment of contact the attacker should feel more less the same as the defender. Here is a catch: in most of situations different parts of the fighters' bodies collide: the attacker typically contacts the front of his leg with the defender's side. The front is harder. Is it hardness that makes the difference? Some web pages inform me, that because of the 3rd law, a fighter should make powerful but very brief hits - retracting a kicking leg before it receives a reaction. But from what I know, if you don't feel a reaction, there was no action in the first place. How is it ever possible to take advantage in martial arts hit and win?

Answer 1

Good question! I've been in martial arts for about four decades and have studied this pretty extensively.

As you guessed, hardness is involved, but it also involves structural strength (which can include some flexibility, as very hard things can break or shatter rather easily).

So, suppose I round-kick a person in the thigh. This is a devastating kick, because I am taking the front edge of the lower third of my tibia, and driving it with speed and force into the soft tissues and nerves of the opponent's outer thigh. His thigh is backed up by the femur -- also a strong bone -- so is unlikely to break. Both my tibia and his muscle tissues and nerves experience similar force and energy. The primary difference is that my tibia is much tougher, stronger than muscle tissue. That muscle tissue and the nerves within it are going to deform, compress and bruise. It is similar to hitting someone in the leg with a bat. Both the leg and the bat experience similar forces, but the bat is just much tougher than the leg.