In many contemporary martial training systems, the concept of kiai has unfortunately been reduced to a mere shout accompanying aggressive action. There is of course a physiological benefit to the kiai shout, though the true concept of kiai goes far beyond shouting alone. Energy naturally produces noise with its release. Crackling fires, thunder claps, fire cracker blasts, and electrical short circuits are all examples of "kiai shouts" from nature. The energy generated and expelled with a lunge, a kick, a throw, or a slash naturally creates a rush of air from the lungs in a similar manner. This rush of air coupled with the momentary tension of the body, including the throat, produces the roaring growl of the true kiai shout

Beginning students of karate, judo, and kendo can be made to shout with the delivery of techniques as a means of learning proper breathing and mental focus. The expelled air prevents the habit of nervously holding the breath with a strike application. The violent noise temporarily diverts the student from worrying about being hit or thrown with a counter technique as he makes his move. The shout can also divert the attention of the student's opponent for a crucial fraction of a second. Until the kiai release of breath becomes a natural part of the fighter, however, it will remain merely an uncomfortable training hand tool, used only in the dojo, and will only contribute to the feeling of artificiality in the martial arts practice session. However, the training hall must reflect the actual world if one is working at learning a combat-oriented fighting art such as Aibudo, and there can be no room for any inhibiting factors whatsoever. Without a feeling of natural spontaneity, a kiai shout is a worthless endeavor. Without thoroughly understanding the point of the shout, and lots of uninhibited practice, naturalness will never be reached.

To create the most effective kiai shout, use a low, open throated vowel sound, and avoid high-pitched shrieks or squealing noises. You want a harsh, totally committed roar, and not a scream of fright The shout is a vocalization of your emotions, and comes up from the diaphragm instead of from the back of your throat

Based on natural emotional conditions, there are four general types of kiai, as observed by past masters.

Attacking Shout

The attacking kiai shout is a fierce explosive noise that causes the adversary to drop his concentration momentarily. Grounded from the .lower abdomen, the shout resonates through the' body to startle, terrify, and over whelm the enemy. Though there are no specific words associated with the attacking shout, a low, drawn-out, almost growling "ehy!" sound is typical for native speakers of Japanese. .

Reacting Shout

The reacting kiai shout is a heavy, intense noise that creates a sense of disappointment in the enemy as his tactics are thwarted. From the tightened midsection, the shout hisses up through the body to accompany the mental charge upon discovering the enemy's hidden weapon, or successfully avoiding his attack The hollow sounding exhalation usually takes a "toh!" form with Japanese speaking practitioners.

Victorious Sound

The victorious shout is a boisterous, triumphant noise that celebrates the overpowering of the enemy. The ringing shouts come from the solar plexus with the exuberance of a laugh, to discourage and bewilder the adversary after a series of blows have been dealt "Yah!" or "yoh!" sounds are natural for Japanese speakers, although the sounds have no word meanings. Native speakers of other languages will produce noises more fitting with their own tonal qualities.

"Shadow" Shout

The fourth shout, or "shadow  kiai!" is not necessarily a vocal shout at all, but rather a total plunging of the body, mind, and feelings into the destiny of the fight If any sound at all were emitted, it might take a "uhmm" sort of quality as this kiai form takes over the ninja's fighting presence by spontaneously blending the characteristics of the attacking, reacting, and victorious kiai shouts in the martial artist consciousness. This is the highest level of Involvement Attackers are used at the crucial moment before a defense is needed, so that the attack is in reality a protection. In touch with the adversary's intentions, there is no surprise and therefore no need to react, in the true sense of the word Finally, even as the victor, one is in danger, in that by defeating another, the desire of revenge is created in the vanquished. Comparisons and classifications fade in their distinctiveness as you immerse yourself in the totalness of the fight, oblivious to the past or future. The only sound left is your breathing in rhythm with the events.

An experience of Toshitsugu Takamatsu illustrates the effectiveness of the living kiai.  Years ago when studying under his teacher, the training hall was disturbed by a huge student from the Sekiguchi ryu bujutsu school. The big man issued a challenge to the togakure ryu dojo of grand master Toda as Toda sensei's highest ranking student, Toshitsugu Takamatsu would naturally have been the one to take on the Sekiguchi fighter. Before the match could even be acknowledged, however, a junior student of Takamatsu sensei leaped to his feet and insisted on meeting the challenger.

The student moved to the fighting area without hesitation and leaped up onto the hardwood floor with a roaring shout and a thunderous stamping of feet Though an older man, the students wide shoulders, scar-crossed face, and neck with its bulging veins gave him a fierce look.  Even though the student was not really a good fighter, according to Takamatsu sensei, he must have seemed convincing to the Sekiguchi ryu man, who visibly flinched backwards in shock as the togakure dojo representative headed for him without any formalities. Realizing what he had done without even thinking, the Seki-guchi student held up his hands, and then bowed in defeat before his opponent had gotten half way across the floor towards him.  When questioned by Toda sensei, the sekiguchi ryu fighter replied that he had been totally taken aback by the little man's scream of indignation and the demonic look on his face. Though probably a better skilled technician than the togakure ryu man, the intruder had been soundly defeated by the power of pure intention alone. ,

The harmony with the universal force implied in the concept of kiai is in no way limited to the body of each individual alone. As in the foregoing story, we can often feel the force of intentions themselves, far ahead of any physical action that may involve us subsequently. Even if no actions follow, we have no doubt experienced the other person's intention. We know they were committed and that they later chose not to follow through with their actions. This bending of the ki force is known as sakki, or "force of the killer." It is the feeling that our intentions project when we are determined to destroy someone else. Animals as well as humans project this sakki as a natural part of their determination to overtake another being. In real life self-protection situations, the ability to blend in with the ki of another and pick up the sakki directed at the target is a crucial skill for emerging alive from the conflict.  That skill is perhaps the most significant difference that separates Aibudo training from the more popular, sport,  martial arts training.

I am unaware of the original source of this Kiai information of which has been modified somewhat.