The use of 'kiai'

(or a shout) in Karate is one aspect of a wide application of breath- control. In order to shout one must breathe out. The obvious point is that sharp exhalation tends to contract the muscles, and particularly the abdominal muscles the use of which is essential for any really solid technique. Another point is that by emphasizing the out-breath (by the same token as that by which one emphasizes the out-breath while laughing) one tends to increase one's confidence, and if this is communicated with the 'kiai' to your opponent his confidence will tend to be correspondingly undermined. A further point is that one's vision is clearer (look at a page of print and breathe out sharply) and reactions quicker during exhalation. It follows from all these points, not only that one should breathe out at the moment of attack, but also that the moment of attack should come when your opponent has just emptied his lungs and can therefore only breathe in.