Why Do Muay Thai Fighters Shout?

September 29, 2020

Walk into any Muay Thai gym or watch any Muay Thai video online, you’ll hear the distinct shout that embodies Muay Thai.


The sound echos around the gym followed by a loud *thud* against the heavy bag or pads. You may wonder why they must make so much sound while training. You may even compare it to the heavy grunter in the commercial gym who’s trying to let everyone know he’s doing a “heavy” bench press.

But Muay Thai sounds and grunts are more than just show. They actually serve a specific purpose when striking.

The Muay Thai scream, grunt, or shout is known as an ‘energy shout’ or ‘kiai’ in Japanese martial arts. Muay Thai fighters make these sounds to ‘stiffen’ the body at impact, increasing the impact force of the strike.

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Utilizing the ‘kiai’ or ‘energy shout’ is a sure-fire way to instantly increase the power of your strikes. But how does shouting make you hit harder?

The Science Behind The Muay Thai Shout

Before explaining how energy shout or kiai helps to develop Muay Thai striking power, it’s important to understand some scientific terms. These being effective mass and double-peak muscle activation. You can read my article “How To Punch Harder” for an in-depth read.

As a brief overview, effective mass when striking is the transfer of momentum throughout the body to the target. The only way that as much momentum is transferred as possible is if the body is completely stiff at impact. Soft structures will deform at impact which decreases the effective mass.

Double peak muscle activation refers to the involved muscle groups in the strike activating just before, or during the first initiation of movement. The muscles then ‘relax,’ and re-activate close to impact. Hence the double peak activation [1].

Why does this occur? The inverse relationship between force and velocity means if you try and throw a strike as fast as possible, little force will be generated. If you try and strike with as much force as possible, velocity is much slower. The double peak muscle activation allows the fighter to simultaneously maximize force and velocity of the strike.

So where does the energy shout fit into this? The energy shout seems to bring upon the second peak in muscle activation [1]. Essentially, by shouting “OH-WAY,” Muay Thai fighters are able to stiffen in the last possible moments of the strike enhancing their effective mass of the strike and therefore, how hard they hit.

The energy shout facilitates the rate of force development (how quickly you can produce force) to go from muscle relaxation during the strike to muscle activation upon impact as quickly as possible to enhance impact force and velocity of the strike [2].

Here’s an exercise you can do at home. Simply breathe out of your mouth as hard and as fast as you can. You should feel your trunk brace like someone was going to punch you or like you just sneezed. This is the stiffness that is created by the ‘energy shout’

What Are Other Benefits Of The Muay Thai Shout?

By performing the energy shout, you’re not only improving how hard you hit, but you are controlling your breathing. Exhaling when throwing a strike will make sure you don’t forget to breathe especially when throwing combinations.

Not breathing while striking will cause you to gas out quickly as you have to try to catch your breath while your opponent is coming at you.

If you want to go down the spiritual side of kiai, kiai is a declaration of your fighting spirit. It is your war cry. It expresses your internal desire to succeed in the current circumstance. All the more reason to use the kiai!

How Should You Develop Your Own Energy Shout?

When developing your own energy shout, don’t try and force a particular sound. Use whatever comes naturally and you will have your own unique shout. There is no wrong sound you can make when striking!

If you feel shy in the beginning, you’ll find you’ll naturally perform a kiai during intense pad work or heavy bag sessions. As you get tired, you will likely shout or grunt as you try and put in the extra effort to keep the power behind your strikes. Now you have discovered your unique energy shout.

While it can be fun shouting loudly during pad work or heavy bag work, it’s a good idea to build good habits for when you face an opponent. Having your mouth wide open while striking can put you in a vulnerable position to get knocked out. Rather, performing kiai with your teeth firmly pressed against your mouthpiece makes sure your jaw and neck are stiff to take any unwanted impact.

Now go develop your war cry!


1. McGill, S. M., Chaimberg, J. D., Frost, D. M., & Fenwick, C. M. (2010). Evidence of a double peak in muscle activation to enhance strike speed and force: an example with elite mixed martial arts fighters. The Journal of Strength & Conditioning Research, 24(2), 348-357.

2. Turner, A., Baker, E. D., & Miller, S. (2011). Increasing the impact force of the rear hand punch. Strength & Conditioning Journal, 33(6), 2-9.

About the author 

James de Lacey

I am a professional strength & conditioning coach that works with professional and international level teams and athletes. I am a published scientific researcher and have completed my Masters in Sport & Exercise Science. I've combined my knowledge of research and experience to bring you the most practical bites to be applied to your combat training.


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