Breathing connects all bodily functions. If you stop breathing for more than five minutes you will die. Breathing is life. Through breathing correctly into your lower abdomen (Ha-Danjeon) you can control your mood and state of mind. The more deeply you breathe the calmer you become.
In martial arts training you must be able to extend one breath to between one and five minutes. This can only be achieved by practicing exercises using your lower abdomen.
This is why in the martial arts you wear a belt. The knot should be placed over your abdomen and you should be able to just place your palm under the knot. When you inhaling push your abdomen out against the knot and when you exhale release the pressure.
Every traditional oriental martial art is based on breathing control not only for health benefits but by moving your internal energy around your body you can generate incredible power.
By breathing into your Danjeon (about three inches below the navel) and breathing out in time with your Taekwondo movements you can maximise your power. Consequently by breathing using your Danjeon you relax the top half of your body so are automatically faster with your upper body and kicking techniques.
Controlling your breathing is the only way you will have full 100% control over your body, which is the overall aim of any martial art. Learning to be in full control of your body and your mind and not letting your emotions rule you takes a long time to master hence the years needed between Dan Grading.