A Kaia does a couple of things. First it throws off your adversary for a couple of crucial seconds at the beginning of your action sequence. His brain will be burning up valuable seconds trying to process what all the yelling is about (Whats he doing!?) while your attack is under way. Very Effective.

The second function of the Kiai is to prompt your brain into action. There's a big difference between thinking of taking action and actually taking action - and its easy for most people to get "locked down" in planning.

Your brain needs a kick to transfer its energy from the thinking and planning mode into the action mode - the Kiai is a verbal "GO" that's imperative to getting yourself moving forward. It's nothing new - Soldiers have been using this for thousands of years moving forward. It overcomes freezing and to strike fear into there enemies.

You will want to use this verbal Kiai in training when you launch into an attack so that it holds power and is an "internal trigger".