Fa Jin is the process of effectively issuing power through movement. This type of power is not the conventional type that we assume regular movements to possess. The type of strike that a boxer throws is, in relation to mass and speed, directly relative to the force that is subsequently received by the target. These types strikes are what make up most combat. An arm's length of distance, or even a bit farther depending on how far back one winds up, is the majority of the distance that will be covered by the object hitting the target. In terms of a strike from a fist, this is limited to how long the individual's arm is. With Fa Jin, the whole body is used in the completing the strike. In the case of a punch: there is a twisting motion that involves the whole body, starting from a properly rooted position, that progresses up the legs toward the torso and shoulders, which is ultimately released at end of fist. This results in a devastatingly powerful blow that contains the wound up energy of not just an arm's length of distance, but the entire length of one's body.
Speed in fighting depends not just on your hands and feet in swiftness.. But other attributes such as nontelegraphic moves and awareness. Speed in fighting is to hit your foe without yourself being hit. This can only be done by hours of practice and being completely fit. Speed in fighting is no good without the power that goes with it.