Traditionally, Taekwondo, as do most hard Karate styles, uses single bone forearm blocks where the edges of the forearm make contact, such the inner forearm block and the outer forearm block. Blocks are viewed as also being strikes that may do damage as well as block. If you block correctly, the pain may cause the attacker to reconsider any more attacks. Some Karate styles, such as Isshin-Ryu, block using double bone blocks where the top or bottom bones and muscles of the forearm make contact. These stylists train using arm conditioning exercises until their muscles seem as hard as bones.
With the inner forearm block, the inner forearm (and palm) faces upward and, if the block moves outward, the striking surface is the radius bone that extends down the thumb side of the forearm. If the block moves inward, the striking surface is the ulna bone that extends down the little finger side of the forearm. With the outer forearm block, the outer forearm (and knuckles) faces upward. If the block moves outward, the striking surface is the ulna; if moving inward the striking surface is the radius.
At and near the wrist, these bones have little muscle or fat padding them. However, as you move upward along the top or bottom of the forearm, the muscles (including the extendor digitorum communis and the extendor carpa ulnaris) and fat layers thicken and serve to protect the underlying bones. However, the sides of the forearm have very little muscle or fat padding covering the bones, with the ulna having the least.
When traditional forearms blocks are used, only one of the forearm bones makes contact with the attacking weapon, and the bone will have little padding. The reasoning is that the bone acts as an edge that will cut into the attacking limb, causing pain and/or injury. However, sometimes the pain and injury happens to the blocking arm.On both sides of the forearm, next to the two forearm bones, are nerves: the lateral and medial antibrachial cutaneous. If struck during a block, these nerves may cause extreme pain. Through Taekwondo training, the forearms are gradually toughened so the pain of impact is lessened.
On either side of the forearm are two major arteries (radial and ulner) and branches of another (brachial). The largest artery is the ulnar, itself having four branches in the forearm. The arteries are relatively close to the surface of the arm near the wrist, and they lay next to the bones. Likewise, major veins run through the forearm and wrist. If either of the two bones in the forearm is broken, a sharp or jagged edge of broken bone may easily tear, penetrate, or sever a nearby artery, vein, or nerve.
A double bone block is when the forearm is turned 90 degrees so that the striking surface is either the inner (bottom) or outer (top) forearm. With this type of block, both forearm bones make contact with the attacking object. A double bone block is much stronger, since any impact is spread across two bones. With two bones blocking, structural strength is essentially doubled. Impact is further dissipated by the extra muscle and fat padding.Anatomically, the double bone block provides more strength and leverage to the block. To demonstrate this on yourself, hold your forearm in a middle inner forearm block (palm upward) and have a friend try to pull or push your arm horizontally. Then try the same thing with the palm facing inward. Which is stronger?
So, should we change our Taekwondo single bone blocks to double bone blocks? The answer is no. Since both the single and double bone block have their own purpose, advantages, and disadvantages, each has its place in Taekwondo. For example, with single bone blocks, if the hand strikes the attacking object, the contact area will be the padded ends of the fist, so the chance of injury will be slight. With a double bone block, the contact area will be either the fragile back of the hand or all the fingers on the front of the hand, which are more susceptible to injury. Also, you would not want to use a double bone inside block against a thrusting knife attack since this would expose the arteries, nerves, and ligaments of the inside of the wrist and lower arm to injury. On the other hand, double bone blocks offer extra structural strength and padding when blocking powerful kicks or hard surface weapons. The single edge of a forearm is useful in striking soft nerve areas or pressure points.
Do you have the time or desire to harden your muscles to the degree necessary to use double bone blocks effectively and consistently? I think not. I use my arms for delicate work, not to mention typing information into TKDTutor.com all day. Also, why punish yourself so you can defend yourself against a specific self-defense situation that for most people will never occur in their lifetimes. It is much wiser to use the single bone to block and use the time saved to work on perfecting other techniques and getting on with the rest of your life.Single bone blocks will continue to be the primary Taekwondo blocks. However, when blocking powerful kicks or hard surface objects, remember the advantages of a double bone block.