The Science Behind Kiai

Kiai is a Japanese term that is used to refer to a short yell or shout uttered when performing an attacking move. Why kiai?

The following is a draft of a passage included in the conclusion to my The Science Behind Fighting Techniques which is in the process of being submitted to a publisher. The conclusion calls on others to build on my work in building a body of knowledge about why a technique works in addition to how to perform the technique.

As I was in the process of concluding this book, Australian Ashleigh Barty played Belorussian Aryna Sabalenka in the 2018 Australian Open (tennis). The Belorussian’s powerful hitting and loud ‘grunting’ was cause for numerous articles on the issue to be published, one of which was by Damian Farrow (2018), professor of sports science at Victoria University: ‘All the racquet: What science tells us about the pros and cons of grunting in tennis.’ He reports that a number of studies have shown that ball velocity increases with hits accompanied by grunting. Can the findings in those studies be extended to kiai, a short yell or shout uttered in Japanese martial arts when performing an attacking move? Increased ball velocity means increased force is being applied when hitting the ball accompanied by a grunt. Can those findings be extended to prove that punches accompanied by a kiai apply increased force on impact? If so, how does a grunt/kiai generate more force on impact with a punch? This is an example of the current lack of biomechanical information associated with martial arts methods and how we may need to be inventive in developing that knowledge base in the absence of direct research.

There are those, many, who will have opinions on this martial arts question, however, they are only opinions. Uninformed opinions at that. My book is designed to turn the many uninformed opinions into informed opinions, which in the process will debunk many opinions.

The studies associated with tennis grunting confirm the increased velocity of the tennis ball accompanied by grunting. They do not explain where the additional force that was applied to the tennis ball was generated from.

The answer to the increased force on impact lies within the concept of kinetic energy. KE is the energy of motion which is transferred on impact. KE is calculated as one half of the product of mass and velocity squared. So which one of the variables of KE does grunting/kiai impact on in order to increase the KE of the arm/racket thereby increasing the force on impact?

The tennis studies limited explanation is highly technical/incomprehensible, however, it would appear to point to grunting tightening the body core which increases the mass behind the tennis strike thereby increasing the force on impact resulting in the increased velocity of the tennis ball. In like manner, a kiai when punching might tighten the body core thereby increasing the mass behind a punch and the force on impact. 

This would fit in with other studies on punching techniques in the martial arts that confirm that the difference in the velocities of punches by experienced and inexperienced practitioners is insignificant but the difference in the force applied on impact is significantly different. This difference is down to the experienced practitioners knowing how to contribute more mass behind their punches.

1. The findings in the studies above goes against everything that has been advised in martial arts and biomechanical texts in relation to punching techniques when referring to the biomechanical concept of KE.

2. There is a study published on the effects of kiap, the Korean equivalent of kiai, on gripping strength. A martial arts 'authority' refers to this study to confirm that kiap increases punching force on impact. It does not, as even the authors of the study acknowledge. It simply confirms that kiap increases gripping strength, so kiap away when grabbing someone. The tennis studies have more to suggest that kiai increases the force on impact than does the kiap study.

3. All of the above is an example of the mindset that is required when attempting to use science to explain martial arts practice. A mindset that is sadly lacking in current martial arts literature. That mindset will be the subject of the next post.