Today, a common injury among young boxers is called the “boxer’s fracture,” in which the outer two knuckles, and sometimes the outer metacarpals of the hand are broken from the impact of an unprotected punch. Even boxing greats like Mike Tyson have broken their fists in this way when engaging in street fights. The danger, however, is significantly reduced through the biomechanics of throwing a bare-fisted punch. Punching in old style boxing was based primarily upon linear action, which emulated the thrust of a sword. When a blow was thrown, a vertical fist was used, rather than today’s horizontal fist that is used in Taekwondo as well as boxing. Some martial art styles used the vertical punch as their primary punching method.
A vertical fist is thrown with the back of the hand facing away from the body, whereas a horizontal fist is thrown with the back of the hand facing upward. This is important due to the skeletal alignment of the arm when throwing a punch. With a vertical fist, the entire arm is extended in one line from the shoulder through to the fist. The elbow is tucked beneath the arm as opposed to jutting out, and the wrist is kept completely straight. This changes the angle at which the fist connects, and maximizes the striking surface by using the whole fist and not just a few knuckles. Even when throwing a “rounding blow,” an ancestor of today’s hook, the vertical fist was used, either normally or inverted (in which the hook is thrown with the thumb facing down, elevating the elbow).
Punching with a vertical fist does two things: there fewer places for the arm to lose energy (as in a bent elbow or wrist) and there is more protection for the arm. The result is that that more kinetic energy is realized as force, and is distributed evenly across the fist. This protects the hand more than if the force was concentrated in one area, while still providing a powerful blow.