1) Difference between Force and Pressure (Force/Area) - This is why a finger jab is more effective than a slap and why punching with two knuckles is more devastating than punching with the entire front face of the fist. A good example is the ease with which you can pierce wood with a sharp nail vs. a blunt one.
2) Impulsive Force (mv-mu)/t - This is the reason you pullback the striking fist as quickly as possible. Note that the change in momentum due to the reversing of direction evaluates the numerator as (mv - (-mu)) = mv+mu along with the denominator t being made as small as possible thus resulting in a larger force. A good example is the game of Billiards/Carrom.
3) Moment/Couple/Torque - This is the reason the side of the body opposite to the striking side is pulled back, waist is twisted and the striking fist uses a screwing motion from palm up to palm down position. The body is kept stable, centered and the force focused. The best example is the classical Karate punch where the non-striking hand is pulled back parallel to the striking hand while both fists follow a screwing/unscrewing twist.
4) Newton's 3rd law - This is why while punching you forcefully push the ground with your rear leg at an angle and twist your waist. The rear leg pushing the ground causes the ground to push back with an equal and opposite force along the leg which is at an angle to the ground. This Force vector can be decomposed into two perpendicular vectors one acting vertically against gravity and the other horizontally in the direction of the strike. This horizontal force is then channeled by the twisting of the waist to the shoulder, hand and fist.
It is all just Physics and Body Dynamics; nothing "Superhuman" :-)