It is important to understand the concept of Kiai. The word is composed of two Japanese words, "ki" meaning "energy," and "ai" meaning "to meet with." "Ki" also means "breath." The kiai is a shout delivered by the karateka (karate practitioner) and is most usually heard when delivering a strike. The combined meaning of the words implies that kiai may be interpreted as a kind of energy that accompanies the strike.
There are two main reasons for using the kiai. One is to frighten, distract, or disconcert, the opponent. The other is to tighten the muscles and empty the breath from the body to prevent injury. This is why kiais are heard both when striking an opponent and when taking a fall.