Karate - Budo The key features and principles for understanding karate The Book >>
Contents

Physical principles of karate

 Introduction History Styles of karate Aims of karate Kihon, kata, kumite Physical principes Bunkai Combat Aggression and stress Kumite in pratice Dangerous spots Japan, Buddhism & Zen Karate and emptiness Precepts Quotations Conclusions References Author Contact The book Annexes JKA Shotokan kata Shitoryu kata Goju-ryu kata Kumite Takedown & MMA Physical training Links

Kinetic Energy: 1/2 mv²

Kinetic energy, i.e. the energy of a moving body, depends on its mass and velocity. In physics, kinetic energy is defined by the following formula: KE = 1/2 mv² where KE is kinetic energy, m mass and v velocity. Kinetic energy is expressed in joules.

We understand, therefore, that the greater the mass and velocity of a blow, the greater the kinetic energy will be.
Mass is linked to the weight of an individual and the technique employed. For example, with a gyaku tsuki, the mass involved is the mass of the arm; but if we add a twist of the hips, the mass of our moving trunk will significantly increase the kinetic energy.

The speed of a blow is very important because it is squared when calculating the kinetic energy. Muscle relaxation, coordination and explosiveness are crucial for increasing the speed. Technique is also important, because in the gyaku tsuki (for example) the speed at which the hips are twisted is added to the speed of the arm extension and the rotation of the fist. If we look at a moving oi tsuki, the entire body advances and the speed of the lower limbs intensifies the energy delivered.

Potential energy: mgh

Gravitational potential energy is the energy of a body resulting from its position in the gravity field. As with any other form of energy, its unit is the joule and it obeys the following formula: PE = mgh where PE is the potential energy, m the mass of the body (in kg), g the acceleration due to gravity (9.81 m/s²) and h the height relative to sea level (in m).

According to the theory of energy conservation, the change in potential energy of a body that moves from height z0 to z1 is transformed into kinetic energy: mg (z0-z1) = 1/2 m (v1²-v0²)

Accordingly, muscle strength and the field of gravity can be used to increase kinetic energy on impact.

During an oi tsuki, the work of the force of the quadriceps whilst moving forward is substantial. Gravity is also used through a controlled forward fall of the body employing a technique based on the anterior flexion of the knee (knee above the big toe) coupled with a very slight forward bending of the trunk.

The technique known as “empty leg” uses the potential energy of the body. The kiba dachi and shiko dachi stances are often used to lower the body in a controlled manner, as at the end of the Heian Sandan kata, to free oneself from a rear hold.

In Tekki Shodan, after the nami gaeshi, the practitioner takes advantage of the controlled fall of the body in a kiba dachi to increase the energy of the sokumen uke. Faced with an opponent who is more powerful, or when muscle strength decreases with age, it is important to refine your technique and learn to use potential energy.

Collision and Kime

It is possible to understand the conservation of the quantity of movement by observing two objects colliding. When, for example, two billiard balls strike each other, the first ball stops moving when it hits a stationary ball, which then begins to move (the energy is transferred). For optimal energy transfer, two non-deformable, non-elastic objects are used. When a ball of dough and a billiard ball strike each other, only some of the kinetic energy of the former is transmitted to the latter; the remaining energy is found in the shape-altering work on the dough.

A contraction of the body (called kime) and a good position at the moment of impact are fundamental in karate. The aim is to make the body of the tori inelastic and “crush-proof”. This allows a better transfer of energy to the uke and avoids the tori’s body being deformed or injured(for example via a dorsiflexion of the wrist during a tsuki).

Pressure: F/A

Pressure is a force acting on the surface area on which it is applied. In the case of a force F perpendicular to a flat surface area A, pressure P is defined by the following formula: P = F/A.

In practice, the pressure exerted on a body is greater when the surface on which the force acts is small. Furthermore, pressure is at its greatest if the force vector is perpendicular to the surface (cos 90° = 1). Conversely, pressure is nearly zero if the force vector is almost parallel to the surface (cos 0°= 0).

In karate, some techniques tend to reduce the impact area in order to maximise the pressure. With a tsuki, it is possible to strike using one or two kentos, in ippon ken, nakadaka ken or hiraken. A further example: with a mae geri or a mawashi geri, it is possible to strike with the koshi.

Ideally, each blow should be close to a trajectory that is perpendicular to the target area. The same applies to a block if maximum pressure is desired (e.g. uchi ude uke or oi tsuki jodan or gedan barai on mae geri chudan). Conversely, if one wishes to absorb an attack, the trajectory of the block must be nearly parallel (for example gedan kake uke on mae geri chudan or nagashi uke on oi tsuki jodan).

Moment of Force

The rotation of a board around a fulcrum (known as a pivot) depends on the intensity of the force and the position of the point of application of the force in relation to the pivot. The greater the force applied at a distance from the pivot, the more efficient it will be. To see for yourself, try to open a door by pushing it near its hinge; next, push it further away from the pivot, for example on its latch.

The above three elements are incorporated into the moment of force, which represents the capacity of a force to rotate a mechanical system around a pivot.

MF = Fp x dop where MF is the moment of force F, Fp the force applied at point p situated at a distance dop from the pivot o.

This principle is useful for understanding how to perform a lock or throw effectively. With an elbow lock, one hand is positioned behind the elbow in order to fix the pivot area. The other hand hyper-extends the elbow by grabbing the wrist or hand at a distance from the pivot in order to increase the moment of force.

Stability and Centre of Gravity

In karate, each part of the body is positioned precisely in order to achieve the stability required for blocking or attacking.
Karate includes multiple positions. In general, if the feet are apart, the knees slightly bent and the centre of gravity low, the body’s stability will be good. Conversely, if the feet are close together and the centre of gravity high, stability will not be so good. However, this second stance allows great mobility and speed of movement.

The search for stability is important in karate. So, during a gyaku tsuki, the back heal should not leave the ground. This error of technique is often committed because the extra height instinctively helps to gain distance and speed. Conversely, at the moment of impact - due to a lack of stability - the heel rise may be accompanied by a step back and an absorption by the tori of some of the kinetic energy that should have been transmitted to the uke.