The Reaction Arm

The reaction arm in traditional martial arts punching and other fundamental movements is quite controversial. The reaction arm is, for instance when doing a front punch, the arm that is pulled back to the hip, while the other fist is flung to the target. Although controversial, for the traditional martial artist there are many proposed reasons for employing the reaction arm. In this post I will mention the two most prominent reasons that I am aware of, as this topic is viewed within ITF Taekwon-Do.

A front fore fist punch with the
reverse arm pulled back towards
the hip. (Image Source)

First, the “reaction arm” functions exactly as its name implies, as a reaction to the punching arm's action. This has a counter-balancing effect. If you were to punch with all your strength and with your whole body weight behind the punch, the resultant force will actually jerk you off balance. Always keeping good structural balance and good posture is paramount in traditional martial arts as the moment you are off-balance or your body structure is unsound, you are strategically disadvantaged, something that your enemy can exploit.

A lot of Taekwon-Do training occurs without hitting an actual target and many of the punches and kicks are done in the air, without any contact. During such training the reaction arm is crucial for keeping good balance and structural alignment. Not doing so may lead to bad habits and overextension of joints, which could lead to long term ailments. However, when you actually do hit something, the reaction arm is not necessarily required because the object you are hitting is providing the reaction force as we know, based on Newton's Third Law of Motion. In other words, when you train against a punching bag or when you actually hit a person, you may at times, and sometimes should, opt to do it without the reaction arm. In ITF Taekwon-Do we actually see this. Certain training is done with the reaction arm (e.g. fundamental technique training), while other exercises are done without the reaction arm (e.g. tournament sparring drills). The discrepancy doesn't mean that the one is “traditional” and the other “practical,” it merely means that one form of training assumes more force that could affect your structure and another form of training that assumes that you will be hitting actual objects.

A knife-hand inward strike with
the reverse arm covering the torso.
(Image Source)

Furthermore, some reaction arm techniques, while aiming to ensure proper balance, also act as guards, covering vital spots on your anatomy. Take for instance the knife hand inward strike where the reaction arm covers the front of your body which has many targets that are potentially easy for your opponent to reach at this close distance. There are quite a number of techniques where the reaction arm seem to have this auxiliary defensive function.

Me demonstrating an arm
bar: pulling with one hand,
while pressing with the other.

The second interpretation for the use of the reaction arm is that it functions as a pull. This is another example where ITF Taekwon-Do seem to base its technical philosophy on Newtonion physics. In this case it suggests that a technique will be more forceful if one combines the oncoming (pulled) momentum of your opponent plus the forward momentum of your own strike. Basically, one can actually pull your opponent into your punch and this will theoretically increase the effectiveness of the strike. It also prevents your opponent from dodging the attack. This is not something one see in most combat sports, not because it is not feasible, but probably because of the nature of the sport and sport equipment—sport rules that discourage grabbing or gloves preventing you from grabbing. When one look at gloveless combat sports like certain forms of Karate, one does occasionally see such pulling-while-punching techniques as in the video below. I personally also like to teach applications where the reaction arm is used to great effect as a grab and pull while attacking with the other arm. This combination of pulling and pushing is a common theme in martial arts.




These are the two main ideas regarding the reaction arm in ITF Taekwon-Do. The first is that it acts as a reaction force that helps with proper balance and postural structure, which is especially necessary when practicing without the presence of a physical target. If you do hit an actual target you may often omit the reaction arm because the object will provide the reaction force according to Newton's Third Law of Motion. The second interpretation of the reaction arm is that it functions as a pull, which combines with the forward momentum of your attack, resulting in a more forceful collision. The reaction arm may also be part of other pull-push combination techniques.

What are your thoughts on the reaction arm?

Read my follow-up post on the reaction arm, which presents a third view based on centrifugal force: "Another Perspective on the Reaction Arm."