Physics of the punch In TaeKwon Do, the punch first begins with the fist at the chest high, though this differs between schools, in the chambered position. It is then accelerated forward at about the height of the shoulder, striking the target with the first two knuckles. The punch, when executed properly, ends it's acceleration with a snap approximately six inches behind the target with the arm slightly bent and with the shoulder in line with the torso, not in front of it. By positioning yourself so that upon contact your arm is slightly bent, the punch will strike the target at a greater velocity than if your arm has already been straightened. This is because your arm will still be accelerating toward the target and will not have stopped its forward momentum. While breaking it is imperative that you do this, otherwise you will probably not create enough force or energy to break the board and it will likely end in an injury to the hand.