Fundamentals of Force

Written by John Coles

All martial arts techniques can be explained using the description ‘push’ or ‘pull’ — or so says West Australian jujutsu instructor John Coles, who has devoted years to writing and researching a book on the biomechanics of martial arts techniques. Coles, a 3rd Dan in Tsutsumi Hozan- ryu jujutsu, 1st Dan in Yoseikan aikido and 3rd Degree in Suci Hati Pencak silat, all under the late, world-renowned sensei Jan de Jong, believes that a better understanding of the scientific basis for combative movements — or rather, their successful application — has long been buried in scientific texts. When revealed, he says, it could change the face of martial arts. He begins here by explaining the fundamentals of force.

Hans de Jong performing a hip-throw

Forces at Work
In Biomechanics: A Qualitative Approach for Studying Human Movement, Ellen Kreighbaum and Katharine Barthels suggest that the visualisation of forces is a necessary skill for, among others, teachers and coaches. This is because forces account for the changes in motion and shape of all things in the environment, including the body and body segments. So, they suggest, it is important to understand what forces are, and how they can be pictured as they are applied to or by a body. (The term ‘body’ is used here to refer to the body as a whole, a body segment, or an object.)

A change in motion refers to a body starting, stopping, speeding up, slowing down or changing direction. Any time a body starts, stops, speeds up, slows down or changes direction, a force has been applied. A change in shape is referred to as ‘deformation.’ The US Committee on Trauma Research’s report Injury in America: A continuing health problem explains that, ‘impact injuries of the human body occur by deformation of tissues beyond their failure limits, which results in damage to anatomic structures or alteration in function.’ Or, in simpler terms, a force acting on a body can deform tissues beyond their failure limits, resulting in an injury.

Think about every technique taught in the martial arts and you will see that they are designed to change the motion of an opponent’s body or to cause the deformation of their tissues in order to cause pain and/or injury. Forces cause those changes. Forces are involved in every technique taught in the martial arts. Forces are what makes every technique work, so it is important for those who teach and study those techniques to understand what forces are and how they can be pictured as they are applied to or by the body. The beauty of it all is that the biomechanical concept of force is very easy for the layperson to understand and apply.

A force is something that causes or tends to cause a change in the motion or shape of a body (‘tends to’ because sufficient force must be applied to cause that change). A force is a very specific action in mechanics. We can talk about a single force or a number of individual forces, each of which can be clearly distinguished. A force is applied to a body and from that body’s perspective, a force is exerted on it. For instance, an arm has internal forces applied to it to move a fist towards a target when punching. The fist then applies a force to the target at impact. The moving arm itself does not possess force.
Forces can be classified as contact or non-contact forces. Most of the forces we think about are contact forces, which occur when the bodies are touching each other. Non-contact forces are those that occur when the bodies are not touching each other. The non-contact force of interest when dealing with violence is gravity.

A force is generally thought of as a push or a pull — and that is it! A force is simply a push or a pull. Kreighbaum and Barthels refer to blows or impacts as examples of a force. Blows and impacts are pushing forces. A force is defined by its magnitude, direction and point of application. Magnitude refers to how much force is applied; but, rather than using a numerical value, we are more interested in relative measures of force when studying techniques from a practical perspective. Direction refers to the way the force is applied — e.g. forward, vertically upward, perpendicular to a surface, or at an angle of 60 degrees above the horizontal. When contact forces are considered, points of application are found by identifying the points of contact between the interacting bodies.
All the techniques taught in the martial arts involve a force or a combination of forces. How do we describe those forces? Very easily:

1.    Identify the points of application of the forces.
2.    Determine if they are a push or a pull.
3.    Determine the direction of the force.
4.    Determine the relative magnitude of the force.
5.    Determine the objective of the combined forces (either change the motion or shape/form of a body).

This simple analysis provides an explanation for every technique taught in all martial arts. It explains what makes a technique work and goes to the very heart of the technique. Jigoro Kano, founder of Kodokan judo, provides an example of the use of the concept of forces to understand martial arts techniques when describing kuzushi (unbalancing) in his 1986 manual Kodokan Judo:

“The basis of kuzushi is pushing and pulling, which are done with the whole body, not just the arms. At times this involves more than just a push or a pull. One may, for instance, push and let go, pull and let go, or push and then pull, or pull and then push. Kuzushi can be done in straight or curved lines and in every direction. Learning all eight basic forms and using them in combinations is indispensible to fundamental judo techniques.”

Kano was the quintessential martial arts biomechanist: ‘the basis of kuzushi is pushing and pulling.’ Kano goes to the very heart of the technique while others complicate the issue with convoluted explanations. The point of application of the applied forces is described by the ‘basic hold’ that a judoka takes on their opponent’s lapel and sleeve. The direction of the applied force(s) can be in straight or curved lines, and the ‘eight basic forms’ refers to happo no kuzushi (eight directions of unbalance), which corresponds to the eight directions on a compass. The use of the whole body rather than just the arms increases the magnitude of the forces applied to unbalance the opponent. The objective of the applied forces is to change the motion of an opponent in order to unbalance them, which enables the execution of a decisive technique.

Teaching With Forces
If students are first taught how to learn, their learning of new skills will be accelerated. First teach them the biomechanical concept of force. Explain that forces are what makes every technique in the martial arts work; that a force is either a push or a pull, and has a point of application, direction and magnitude; and that the purpose of applying a force is to change the motion of an opponent, or to deform their tissues in order to cause pain and/or injury. Then consistently teach techniques using this force-based approach.

In Kodokan Judo, Kano is very consistent in describing techniques in force terms. The descriptions provide succinct instruction as to how to execute the technique because they focus on what makes the technique work. Kano’s instruction for ogoshi (large hip throw) is representative of the better quality instruction provided by instructors: ‘To execute ogoshi, you break your opponent’s balance directly forward or to his right front corner, load him onto your right hip, then raise your hip and twist to throw him.’

Kano used an analytical method to understand and study his techniques. He divided the execution of a technique into stages: kuzushi (unbalancing), tsukuri (‘fitting-in’) and kake, (execution). Let’s analyse Kano’s description of ogoshi using these stages: kuzushi – break your opponent’s balance directly forward or to their right front corner; tsukuri – load them onto your right hip; kake – raise your hip and twist to throw the opponent. Now let’s look at each of these stages in force-related detail.

Kano provides the following force-specific instruction for the kuzushi stage: ‘Pull your opponent toward you with your right hand so that he steps forward with his left foot.’ The instruction covers the point of application (right hand on the opponent’s left lapel), whether it is a push or a pull, and the direction and objective of applied forces (change in motion).

The tsukuri stage: ‘Quickly slip your right arm around his waist and draw him toward your right hip...pivot around...bend your knees and pull him right against your right hip.’ Again we have point of application, whether or not the force is a push or pull, and the direction and objective of applied forces.

The kake stage: ‘Lift him up by straightening your knees. At the same time, pull with your left arm and twist to the left. Your opponent will turn over your hip and fall on his back in front of you.’ Again, we have point of application, whether or not the force is a push or pull, and the direction and objective of applied forces. It should be noted that straightening the knees in the kake stage is applying a pushing force with the back of the thrower’s hip to the front of the opponent’s hip in order to lift their feet off the ground.

I raise one question here: What is happening with the right arm during the kake stage? The left hand is pulling the right upper sleeve of the opponent around the body, but what is the right arm doing? The last we heard of the right arm was during the tsukuri stage, when it was placed around the opponent’s waist, drawing (pushing) them towards the hip.

In her book Judo: A Pictorial Manual, Aussie judo and jujutsu pioneer Sensei Patricia Harrington gives similar instruction for the tsukuri stage of the throw but provides the following instruction for the kake stage: ‘Throw your partner forward with a fast, explosive action.’ It has to be said that this instruction is not very helpful in explaining to a student how to throw their partner in a fast, explosive action, but throw their partner in a fast, explosive action is exactly what you want the student to do. When I was instructing jujutsu for Shihan Jan de Jong, OAM 9th Dan, I found that many students had difficulty in throwing their partner in a fast, explosive action with ogoshi. The reason for this was that the students were doing exactly what their instructors had instructed them to do.

The thrower loads the opponent onto their hip during the tsukuri stage by placing their right arm around the opponent’s waist and pushing them tight against their hip. The left hand pulls on the opponent’s right upper sleeve during the kake stage in order to turn the opponent over their hip. The force applied by the right arm during the tsukuri stage acts in opposition to the force applied by the left hand during the kake stage. When I changed the standard instruction to the right arm pushing around the thrower’s body during the kake stage, the students were then throwing their opponent forward and down with a fast, explosive action. The forces applied by the left hand and right arm were now working in unison during the kake stage to achieve the objective of the technique.
Everybody understands what a push or a pull is. If a student is told to push or pull in a certain direction, they will do so. If that instruction is not an accurate or complete description of the forces involved in the execution of a technique, do not be surprised if the student experiences difficulty in performing the technique.

A force-based approach ‘forces’ us to consider each and every point of contact where a force may be applied. All of these forces contribute to, or at times hinder, the execution of a technique. A complete analysis of the forces involved in the technique — and a complete analysis is so simple — avoids these issues.

Law of Reaction
Isaac Newton’s third law of motion states that for every action there is an equal and opposite reaction. Newton uses the words ‘action’ and ‘reaction’ to mean forces. When a force is applied to a body, that body responds with a reaction force that is equal in magnitude and opposite in direction to the action force. When we hit a body, that body ‘hits’ us back. The forces may be equal in magnitude but the effect of those forces may differ, because they are acting on different bodies with different characteristics. For instance, nothing may happen to a brick wall when we punch it and apply a force at impact, but the equal and opposite reaction force that the wall applies to our hand may result in an injury.

An understanding of action and reaction forces is particularly useful when understanding and studying striking, kicking and blocking techniques. The late head of JKA Shotokan and author of Dynamic Karate (1966), Sensei Masatoshi Nakayama, divided the stages of a karate technique into ‘before’, ‘during’ and ‘after’ impact. No forces are experienced during the before and after impact stages, but action and reaction forces are experienced during the impact stage. Stances need to have a higher degree of stability (resistance to unbalancing forces) during the impact stage to deal with action and reaction forces, and less stability (more mobility) during the before and after impact stages to facilitate evasion and/or moving into position to attack.

Force Simplified
Forces are involved in every martial arts technique and are what makes them work, by causing a change in motion or the shape/form of a body. A force involves the interaction of two bodies and is either a push or a pull, and has a point of application, direction and magnitude. Every action force has a reaction force. So, teach and learn with reference to the essence of techniques: forces.

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