Many of my kendo friends are aware that I drone on endlessly about sae or snap. Often kendoka who have good kihon and timing, fail to make decisive ippon because they do not finish the strike sharply.

This could be because they are using the too much right hand power or because they are pushing the shinai forward rather than cutting down. Often though, lack of sae is caused by ineffective kiai. It’s hard to explain this without demonstrating, but if your kiai is slow, lacks energy or comes before or after the point of impact, then it will not help you make a successful attack.

Kiai should be sharp and explosive and delivered exactly at the moment you hit the target. Its purpose is to focus all your physical and mental energy on the cut. It emphasises that nothing else exists for you at that moment, only your total commitment to the strike. Some people believe that kiai is made to alert the shinpan that they have scored a point, or that it is a declaration of intent, a bit like naming the pocket in a game of pool. This is far from the truth. Premature kiai means that your energy tails off too early. Using it to claim your point means that your energy peaks after you need it most.

Your kiai should be made in the spirit of sutemi, throwing every last particle of air into a totally unselfconscious scream as you hit. It will naturally continue briefly as you move through into zanshin. In fact a sharp single kiai will automatically make you accelerate past your opponent. Do not be tempted to elongate your kiai into something like the noise of a car with starter motor problems. Me-e-e-e-e-en simply makes you sound needy.

The mechanics of good kiai are simple. We have looked at them when we talked about seme and tame. You take a big breath in through your nose when you are still in safe distance, then let half the air out as a kakegoe shout; something simple like” ya”. Holding the remainder of your breath in your abdomen you step into your striking distance. Once you have broken your opponent’s centre or pre-empted his attack, raise your shinai and strike down at the target in the timing of one, expelling your remaining breath as kiai. The idea is not just to focus your shout but to commit your entire spirit.

（原文http://kendoinfo.wordpress.com/2013/08/26/kiai-and-sae/）