Why You Should Kiai

There was some UFC card the other weekend where many female fighters were kiai-ing with every strike, and I saw an unrelated debate on an online forum about the value of the kiai. Most of the commentary kind of missed the point of the kiai, so I thought I'd weigh in.

What is a kiai?
In case not everyone means the same thing when they say 'kiai,' allow me to clarify. A kiai is a quick, loud (more or less as loud as you can make it) shout that is done pretty much at the point of contact for a strike (or block, I guess, though more often a strike). A proper kiai should have no hard consonant sounds in it, though some people kiai with some 's' sounds in it. A super loud 'ha' usually does the trick. The louder the better, and it should not drag on for several seconds (you do see that long drawn out scream in some performance kata, but I believe that is a mistake). And the shout is supposed to come from the belly, not the upper chest (which is necessary if you want to make the loudest sound).

What are the benefits of a kiai during a match? (short answer: not much)
It's a fun little trick to stand close to somebody who isn't ready for it and kiai, to demonstrate the way their body locks up. It would be nice if performing a kiai during a sparring match or a 'real' fight would have the same effect, and maybe it could, but I rather doubt it. When someone is ready for you, facing you, and psychologically prepared for some kind of combat, I highly doubt yelling at them is going to have any significant impact.

A secondary possible benefit of the kiai during a sport competition is to help convince judges that you have, in fact, scored a point or a significant blow. I have heard this from more experienced competitors, and I'll put it out there as a possible good reason to kiai during point fighting or even contact fighting (in situations where judges sometimes render decisions about the fight outcome).

What are the (psychological) benefits of a kiai during training?
Some people (maybe most?) can feel energized by being in a class full of like minded people shouting loudly as they execute techniques. Some feel this is a display of strong karate spirit.

I am absolutely on board with anyone who sees this as a benefit. On its own, I don't see that it justifies the importance we place on the kiai in training, but there are other reasons (see below!)

What are the physical benefits of a kiai during training?
Now we get to the bread and butter of this post.

I don't talk about the 'core' enough, but here's the idea in a nutshell:
1. Your upper body (ribs, shoulders, arms) is connected to your lower body (hips and legs) by your spine.
2. Your spine is not rigid. It can bend and twist in all kinds of directions.
3. When generating power from your lower body, and transmitting it to your upper body, the more your spine twists and bends the less efficient the power transmission. Imagine trying to hammer in a nail with a pool noodle.
4. When transmitting power through your spine, you need the muscles in that region to contract, making the link between your upper and lower body as rigid as possible (it won't be perfectly rigid, that's okay, but you don't want to be floppy either).
5. Those muscles are collectively referred to as the 'core.' The core is a bunch of muscles, some of which you can see (if you're lean enough, like what people call 'abs' and lats) and some of which are 'deep' (meaning closer to the spine).
6. Even if your core muscles are strong, you have to be able to contract the right ones at the right times in the right pattern to get the most stiffness in your core.

Why am I saying all this now? Because one of the best ways to make sure that those deep core muscles are activated (working) is to make a hard, deep exhalation (blow out), using the diaphragm (so breathing from the belly, more than from the upper chest).

In fact, in sports performance, lots of strength coaches are making a big deal out of having their athletes exhale forcefully, from their bellies, when they want to perform high force movements.

Now guess what?

You can't kiai without making a forceful, deep, diaphragmatic exhalation. The exact kind of exhalation that maximally engages the deep core muscles and stabilizes your core.

Now of course you can contract those muscles without exhaling, and you can exhale without shouting. But the cue (the instruction) to kiai is an external cue, which is generally better than an internal cue (like, "squeeze your abs really hard"). For many people, especially not-great-athletes, shouting comes fairly naturally, while controlling the deep core muscles requires a lot of concentration.

Another advantage of the kiai is that an instructor can hear it. You can sort of tell if a student has a floppy core when they punch, but it's much easier to hear that someone's kiai is weak. It's a fast diagnostic that can help you figure out quickly if there is something particularly wrong with the way a student is executing a technique.

In short:
1. A kiai, because it requires a hard exhalation, will force the core to contract, stabilizing the torso and improving power transmission from the lower body;
2. A kiai can be heard, making it easy for an instructor to make sure the student is exhaling at the proper time, with the proper force.

When you should kiai
I wouldn't argue that students should kiai with every repetition of their training, every class. I think it would make your throat hurt and make classes kind of annoying. And I think that our goal should be to learn from the kiai how to use our core, so that we are able to do it without thinking and without shouting. In other words, I think the kiai should be seen as a great training tool for relatively newer students, and something to be used more sparingly with more advanced students.

But for those who think the kiai is 'just dumb' or 'pointless,' I say that it's a very effective and simple way to teach students how to use their deep core muscles, and that's extremely valuable for instructors.