It varies depending on the technique, but in most Japanese martial arts, the "shouts" are kiai and serve two functions: It tightens the diaphragm and chest, making it easier to take a hit. It adds "energy" to the strike by causing you to focus on the moment of impact. There are several types of shouts in Aikido. The most common type is the "release" shout. This is used at the end of a move to let out the tension and preserve energy for the next attack. The release shout is often accompanied by hand gestures to further accentuate the release of energy. For example, before throwing someone into a wall, an attacker might yell "oho!" (or some similar word) to signal their intention and then follow up with the release shout as they throw their victim toward the wall. Another type of shout is the "stop" shout. When you use this type of shout, you are telling your opponent that they should stop what they are doing right now! The stop shout is usually followed by a verbal command such as "backdown," "surrender," or "attack me." Yet another type of shout is the "challenge" shout. With this type of shout, you are calling out to your opponent to come at you so that you can practice your skills against them. Most often, the challenge shout is followed by a request for permission to attack.