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?