There are 9 weapons on the human body - the two hands, the two feet, the two elbows, the two knees and the head. Some martial arts also use the shoulder while the hips play a really important role in an art like Judo. On this page, the discussion will focus on the hands primarily.
Hands may be used fully open, partially open or completely closed, tensed or relaxed, in a forehand or backhand motion. An open, relaxed hand may used as a slap (forehand) or as a whip (backhand). A rigid hand may be used in a chopping action to the throat, a ridge hand to the carotid artery, or as a stab to the solar plexus. Partially closed and relatively relaxed, the tips of the fingers may be used in a side-to-side motion as a rake to the eyes, with only some fingers extended as a eye poke (index or thumbs) or eye hook. Fully closed, the fist may be used as a hammer to the groin, a whipping back knuckle to side of the temple, or as a punch to the face. And these are not all of the uses of the human hand as a weapon.
When using the hands as a weapon, consider the target. A relaxed open or partially closed hand should only be used on soft targets and nerve endings as fingers can be broken. And remember that bone on bone targets are to be avoided, while bone on flesh targets are usually safe. Flesh on bone targets won't work at all.
The key to power in any strike is speed, not mass. This comes from the laws of physics about kinetic energy, the energy possessed by a moving body.
E = 1/2 mv2
E = kinetic energy
m = mass of the object
v = velocity of the object
In this equation, one cannot change the mass of the hand or foot, so the only quantity that can be changed is the velocity (speed in a particular direction). The key to speed is relaxation. Any motion within the human body is controlled by muscular contraction. For every muscle assisting in a forward motion (agonist), there is a muscle that controls the reverse motion (antagonist). When agonists and antagonist are contracted in equal measure, the physical body doesn't move, but becomes rigid because the forces applied are equal. If the antagonist is relaxed (force applied = 0), then the agonist moves the body member. Similarly, when the agonist is relaxed, the body member reverses direction because of the unbalanced force of the antagonist.
A punch works by extending the arm, and tightening the fist at the end, then flexing the arm to retract it. The agonist for extending the arm is the tricep on the back of the arm, and the antagonist is the bicep (very simply put as there are other muscles involved). To experience this yourself, curl your right arm so that your fist is near your shoulder. Gently squeeze your upper right arm between the four fingers and thumb of your left hand. The bicep will feel harder (front of the arm), tighter than your tricep (back of the arm). Now extend your arm as if punching at shoulder height. The bicep will soften while the tricep will harden. So if you want to punch more quickly, you have to relax the bicep. To snap it back, you have to relax the tricep and contract the tricep.
Rigid, Closed Hands - The Fist
The most basic formation of the hand is the full fist. While there are some variations in the fist, a beginner should use only one. To properly make a fist, start with the hand completely open. Close the fingers into the center of the palm as tightly as possible. Close the thumb over the middle bones of the first two fingers. Do not put the thumb inside the fist. If you hit something hard with your fist and the thumb is inside, you will break it. Do not leave the thumb hanging freely in its normal position as you might catch on something and break it. The only place for the thumb is over the outside of the middle bones of the first two fingers. The fist must also be tight. You can check this by quickly opening your fist - the palm will be white and will return to normal color as blood flow is re-established.
The striking areas of the full fist are the first two knuckles in a punch (jab, reverse, hook, uppercut), and a back knuckle strike, OR the butt of the fist used in a hammer fist strike (striking as if holding a hammer and using the butt of the hammer handle as the weapon). Any time the fist is used, the back of the hand must be flat and match the line of the forearm. It should not be cocked forward to the inside of the wrist or be allowed to fold backward toward the elbow as that will cause a sprained or broken wrist. It is important to use your tools wisely, and not break them.
There a couple of variations on the full fist. The first is known as the half-fist. Instead of curling the fingers entirely into the palm, then closing the thumb, only the first two joints of the fingers are bent, and the last joint (nearest to the palm) is left straight. The thumb is tucked into the palm with the nail just inside the edge of the palm. The striking surface are the second knuckles of the index and second finger.
The second variation is called a middle finger fist. In this variation, the middle finger is left slightly uncurled than the rest of the fingers and is braced by the index and fourth fingers so that it protrudes from between those fingers and becomes the principal striking surface. It is important to remember not to strike that finger from the side as it will suffer the same fate as an extended thumb. So any strike must by straight forward in line with the wrist, or just through the palm.
Rigid, Open Hands - The Sword Hand, Ridge Hand et Al
While the fist is the safest, rigid hand strike, it does not fit with all of the possible targets because it is rather blunt (hence, the usage of the word "mace" in self-defenses using hammer fists like "Alternating Maces"). An open, rigid hand with the thumb tucked into the palm works better for other targets like the throat, the solar plexus, and the eyes.
It may be used as a ridge hand (using the bone at the base of the thumb), a sword hand (using the side of the hand next to the smallest finger), a 1, 2 or 4 finger stab or a 2 finger hook with the hand in line with the flat of the forearm and the fingers either completely straight, or with the tips slightly bent. With the wrist bent 90° back towards the elbow, it may be used in a palm heel strike (known as a "Salute" in Kenpo), or as a slice using the finger tips. With the thumb extended, it may be used as a claw or rake with the fingers and thumb bent, or with all the fingers and thumb clustered together in an eagle's beak (used in a frictional pull in Snapping Twig, Purple, Level 1). And finally, the thumb may used as a jabbing weapon with all of the fingers closed, and the thumb extended and braced against the side of the first finger. That is why the Finger Sets exist in Kenpo (in Blue, Level 1, and Purple, Level 2) to illustrate some of these alternative uses and prepare the student for new ideas. See the pictures of some of these alternatives below.
It is also important to note, that almost without exception, the thumb is tucked inside the palm. Retracing the thumb to the inside of the palm is part of making the hand into a rigid body. It also has a safety aspect.If an opponent can grab an exposed thumb, they can either break it or use it to force you to the ground. With the thumb hidden, it is much harder to grab.
Relaxed, Open Hands - The Parry and Check
If your hands are open, they can be used to change the direction of an opponent's attack (the parry) or to maintain the position of an opponent's weapons (the check). If you practice the four count, "Block, Parry, Check" drill (the fourth count being the returning strike), you can see examples of both the parry and the check. The block stops the incoming blow, the parry repositions the weapon, and the check sets the weapon in the new position while you return a blow of your own. Both the parry and the check do not have the same force behind them as the block. They are much lighter, the circles or lines much smaller. That is why they are safe for an open hand.
The open hand can also be used as a finger whip to the eyes or the groin. In particular, the whip to the eyes will distract the opponent, and as the late Dave Hayes (Kick Boxing, Kung Fu, Goju Ryu and Boxing) used to say, "Anything that can distract you, can knock you out". The autonomic reaction of the eyes to incoming fingers will force the lids shut, a blink ,and give you the opportunity to put a more devastating strike behind it. Timing is everything.
Sensei Doug Reed and Sempai Tony Reed demonstrate the "Block, Parry, Check" drill.