Traditional Japanese Dojo generally use single syllables beginning with a vowel. The concept has become a notable part of Asian martial arts in popular culture, especially in martial arts films, in writing rendered in variants such as Hi-yah!, Aiyah!, Eeee-yah!, or Hyah!.
The term is a compound of ki (気) meaning energy or mood, a(u)(合), an emphatic marker. The same concept is known as K'ihap in many Korean martial arts, such as taekwondo and Tang Soo Do, ki being the energy and hap meaning to join, to harmonize, or to amplify, based on the Korean reading of the same characters; its Hangul spelling is 기합.
Students of Japanese martial arts such as aikido, karate, kobudo, kendo, or judo (or related arts such as taiko drumming) use kiai to startle an opponent, intimidate, express confidence, or express victory. In kendo, for example, a point is only given by the Shinpan (referees) if the hit is accompanied by a strong, convincing kiai. A kiai can also be used in addition with tightening the core muscles to prevent damage to the stomach. The physical aspects of a kiai are often thought to teach a student proper breathing technique when executing an attack which is a common trait adopted by many other foreign martial arts and combat sports.
This is especially useful for longer series of attacks such as kirikaeshi, Kakari geiko (rapid partner exercise creating openings) and uchikomi geiko (responding fast to openings made by the partner).
Mental imagery techniques are used to teach the martial artist to imagine starting a kiai in the hara or dantian; from a physiological perspective, this means the yell should start in the diaphragm, not the throat.