An important aspect of martial arts that relates to breathing properly is what we call the “Kiai.” When you hear a student give out a loud yell during the execution of a move, you are hearing them “Kiai.” It is pronounced Key-Eye.

One of the reasons we develop and deliver the Kiai as a martial artist is that it can be tool to distract, startle or intimidate an opponent, giving us a strategic advantage. It can also be used to “psych ourselves up” – to inspire us to fight with everything we have to protect ourselves or a loved one.

There is also a physical aspect to the Kiai. When you throw a punch or a kick or deliver a block, by also delviering a Kiai at the moment of impact, you increase the force of the blow and its effectiveness. Additionally, if you deliver a Kiai when you get hit, it reduces the damage done to your body by the attack. A Kiai is a short, sharp, loud breath that begins in the navel or diaphragm (not the lungs). The word you say when you Kiai is less important than the proper physiological technique in its delivery. Many people say “Hup” or “Kiyap” or something similar.

Great article on the Kiai & Fighting Spirit:

What Every Karate-ka Should Know About “Kiai!”