Understanding The Forces Involved in Judo

by : Jimmy Cox

We know that there are many kinds of force around us. How are they made use of in judo? Let us now study two of them.

Muscular force

According to Newton's second law of motion, you have an advantage over your opponent when your body is larger than his. Besides that law, however, there is another factor that gives you advantage over a smaller opponent. This is the large muscular force with which a big man is usually gifted. He can carry a heavy block or lift it easily with both hands, whereas the same feat may be difficult for a smaller man.

Although we can say that large muscular force is very convenient for breaking the opponent's posture in judo, muscular force alone does not encompass all the forces used in judo. To make use of muscular force normally and effectively, you must study its nature.

One of the important facts about judo is that successful employment of techniques is the result of total body muscular movement - as, for example, in the execution of an over-shoulder throw.

The same thing can be said about making one's opponent fall or about strangling him. Defensively, too, it might be difficult to save yourself from your opponent's attack were it not for your ability to use all your muscular force. In bending your opponent's joints in reverse, the same rule applies. We can therefore understand that the exertion of a strong force means that muscles must act together by the use of the force of the waist and abdominal region.

Expert judo is characterized by a large variety of techniques. As you observe, you will notice that the expert makes good use of many kinds of forces. Since judo employs many forces, such as those of gravity, momentum, and friction, you must not mistake muscular force for the only effective one. If you do, your judo will become hard, heavy, slow, and ineffective.


In judo it is important to throw your opponent by making use of his loss of balance. One of the laws at work here is the law of gravity. We know that Sir Isaac Newton discovered the law of gravitation by seeing an apple fall from a tree. All bodies in the universe attract one another.

Now let us consider the application of the law of gravity to judo. The heavier the opponent, the more difficult it is for you to move him horizontally. It is even more difficult for you to move him vertically. On the other hand, a larger gravity acts on him to make him fall.

In judo gravity may be represented as a force pulling the opponent downward. If you want to make him fall, you make him lose his balance; that is, you cause his center of gravity to go outside the base. Then the gravity that acts on him works for you to make him lean or fall. Let us study the action of the law of gravity by illustrations.

You (A) and your opponent (B) are standing face to face. He advances toward you to take hold of you by the left lapel. At the same time you withdraw as much as he advances. If he is mentally or physically unable to let his advanced foot advance again, he will lean forward, lose his balance, and fall. Also, it is obvious that the same thing will happen when the stability of the legs supporting the trunk is taken away.

When your opponent takes a larger step forward than usual, you merely sweep his advanced foot away in the direction of his advance (de-ashi-harai, or advanced foot sweep). By doing this, you will drop him with the gravity acting on him directly.

Many forces can be used in judo, but muscular force and the force of gravity are two of the most crucial.