Breaking (kyuko) is used as a way for martial art students to measures the precision and power of their hand strikes and kicks.
Most rank testing requires patterns, self-defense, sparring, and breaking. Because offensive techniques may be fatal, students are not able to use full power when practicing against an opponent. By breaking solid objects, such as boards and bricks, they may measure their accuracy, concentration of power, and strength of will. Breaking is not taught to beginners, only to color belts and black belts.
If asked about breaking, most people think about spectacular martial art demonstrations. However, this is only a superficial understanding of breaking. The purpose of breaking is to build confidence in students by letting them test their power and see immediate results. Breaking requires executing techniques with precision and power.
Demonstrating breaking in front of a crowd may boost the ego but the real benefit of breaking comes from the confidence it gives the breaker. To build this confidence, the breaking does not need spectators.
Anyone may break one board with brute strength, but strength alone begins to fail as the number of boards increases. Only concentrated power and precise techniques will prevail when breaking more than one board. Advanced breaking techniques are not measured by the number of boards broke, but instead by the difficulty of the technique itself. To break more than one board requires training and study of the wood itself, such as its composition, hardness, how the grain of the board is positioned, and the curvature of the board. To break consistently and with thicker mediums, you must learn to snap your body mass into the technique. For instance, if you only use your arm to punch, its power will be limited by its mass and the strength in its muscles. If you use body snap, you add the mass of the body to the power of the punch.
To train to break boards, the breaking surfaces, such as hands, feet, and elbows, should be conditioned by striking a padded board (forging post, tollyon-chu in Korean, makiwara in Japanese) to build callous, bone and joint strength, and pain tolerance. Practicing hyungs builds the timing, balance, breathing, focus, and strength needed for board breaking. Sparring also develops breathing, muscle contraction, timing, and focus. Along with the training proper nutrition is also important. Breaking is the culmination of everything you have learned in Taekwondo training.
Board breaking requires proper training and technique, but it more of a exercise in mental preparedness. You must overcome your fear and apprehension and break a board or boards with your little fragile hand. Remember that thousands of students just like you have broken boards with no injury, so it must not be as dangerous as it first appears. To break a board, you must mentally prepare yourself to hit the board with full speed and power with no regard to possible injury. Only then will you accomplish the break. Remember, it only hunts when the board does not break. I have never seen a student injured during rank testing breaking, but I have seen many students not complete their breaks because of a fear of injury.