Aside from joining along in a classic Tears for Fears song or yelling at your kid not to bolt across a busy street, you don’t have much occasion to shout it out in real life. Except, of course, if you spar or do forms in karate. Then you shout quite a bit. And that goes double for tournaments.
As explained in this post on Black Belt Wiki, the “shout” in traditional Japanese karate is called a kiai. It does a lot. The kiai generates power in the body. It helps you breathe (vs. tense up). It’s used to make your opponent hesitate, to draw back. To impress judges. To command inner and outer forces in one vehement summoning of spirit.
To put a point on the shout’s importance, think of your last attempt to call a group of rowdy or unengaged people to attention. It’s not easy. It can be intimidating. And you can’t go and whisper to each person one by one to “please quiet down and look up here.” It just doesn’t work.
Then think of Master Macy’s or Mr. Worth’s shouts. (Yeah, you can probably feel your nerves go taut just imagining them). They command the attention of 100 people, students and parents, passersby on the sidewalk outside. It’s like a thunderclap. You respect it. And you stand at attention for just one split second while you anticipate what’s coming next.
And when you’re dealing with the roar of a thousand karate voices at a tournament, your kiai has gotta cut through. Don’t just aim for the judges attention. Get your shout to bounce off the cinder block walls and back to the surrounding competitors, your teammates and the onlookers. You want them to watch. You need to make them feel it.
When you’re in command of your kiai you’ll feel your muscles ripple, you’ll feel the power in your chest. You’ll feel it radiate almost instantly through your whole body.
The rest is hard to define. Ultimately the kiai has to do with confidence, developing it as well as projecting it. Check out this post and the accompanying videos for help in finding your karate voice.