#18 Principle of Leverage 梃子の原理


I think everyone knows that circular movement is an important element in Aikido. It’s easy to imagine that the centre of gravity becomes the centre point of circular movement when turning body.

However, it is not easy to use the principle of leverage at the same time as circular movement.

In the beginner's class, the following things are often seen.
> Step to the wrong place
> Fail to make a strong centre line
> Fail to set the fulcrum of the leverage
> Fail to connect continuous circular movement

Conversely, if you can enter a right place and create the strong centre line and set the fulcrum of the leverage at the correct position and successfully connect the movement of the continuous circle, it will be the perfect movement.

Well, it's easy to say, hard to do. Then here, let's recall the equation of motion, F=ma, you studied at school.

First, the principle of leverage and circular motion are the same things in physics. When drawing a circle, trace the circumference by firmly fixing the centre point. When playing with a seesaw, fix the fulcrum firmly and move up and down on the circumference. This is the same as rotating the lever with the fulcrum as the centre point.

Second, the velocity vector of the object moving on the circumference is in the direction of the tangent 90 degrees. This is because the centripetal force and the centrifugal force are balanced. If the balance collapses, the object will move away from the circumference and the circular movement will disappear.

Third, if the moment of inertia is large, the object will not be easy to rotate. The moment of inertia is determined by the position and direction of the axis of rotation.

Fourth, the principle of leverage is (weight of object) × (distance from fulcrum to action point) = (force) × (distance from fulcrum to force point). In order to ease using the lever, bring the fulcrum closer to the action point as much as possible, and make the force point as far as possible from the fulcrum.

From the above, we can understand the followings.

1. Create the strong centre line to set the centre point of circular movement.

2. When you turn the body by "Tenkan" movement, lead the opponent in a tangential direction.

3. In order to reduce the moment of inertia, bring the centre of gravity of the opponent as closely as possible to your centre line.

4. To use the principle of leverage, set the fulcrum as close as possible to the centre of gravity of the opponent, and set the force point as far as possible from the fulcrum.

If you cannot set the fulcrum to the correct position, let's practice the grappling techniques such as "Katate-tori", "Ryote-tori", "Morote-tori", "Kata-tori" with Static. Focus on finding the lever in movement rather than trying to throw the opponent.

It is important that the centre line does not shake when turning your body. After understanding the principle of leverage, you will add human physiology such as controlling the elbow.

Thanks for reading.




> 間違った場所に入身する
> 強い中心線がつくれない
> 梃子の支点を設定できない
> 連続した円運動ができない



第一に、円運動と梃子の原理は物理学において同じ意味です。 円を描くときは中心点をしっかり固定して円周をなぞります。 シーソーで遊ぶときは支点をしっかり固定して円周上を上下します。これは、支点を中心点として梃子を回転させているのと同じです。



第四に、梃子の原理は(おもりの重さ)×(支点から作用点までの距離)=(力)×(支点から力点までの距離) となります。梃子を使って楽をするためには、支点をできるだけ作用点に近づけ、力点はできるだけ支点から遠くします。


1. 円運動の中心点をつくるために強い体の中心線をつくる

2. 相手を伴って転換する場合は接線方向に相手を導く

3. 慣性モーメントを小さくするために相手の重心を自分の中心線に出来る限り近づける

4. 梃子の原理を使うには、相手の重心になるべく近いところに支点を設定し、支点からできるだけ遠いところを力点とする

梃子の支点を正しい位置に設定することができない人は、Static practiceで片手取りや両手取り、諸手取り、肩取りなどのつかみ技を繰り返し練習しましょう。相手を投げようとせず、動きの中に梃子を見つけることに集中しましょう。




テーマ : 合気道
ジャンル : スポーツ

#17 “Kuzushi” movement with Katate-tori 片手取りの崩し


"Kuzushi" (balance breaking) is movement which provides rotary or vertical motion to the body of the opponent.

With the "Katate-tori", you take "Tenshin" step by 90 degree to give a rotary motion, and take "Tenshin" step by 45 degree to give a vertical motion.

If you are able to control the opponent's movement by giving "Kesagiri-Atemi", you can do “Irimi Tenkan” step to give a dynamic rotary motion.

In particular, sink the whole body when you give the opponent a vertical motion. Don’t try to push his arm down by force.

When the opponent stops, he becomes stable in the centre of gravity. This is why you must not stop movement of the opponent. Let’s keep Uke’s movement alive.

Thanks for reading.









テーマ : 合気道
ジャンル : スポーツ

#16 Tenkan - Understanding of the inertia force 転換動作


If you bring the centre of gravity close to a centre axis, you make the moment of inertia smaller. Consequently, you can quicken the rotating speed of the object.

In other words, if you stretch out an arm and a foot, the centre of gravity moves to the outside, and the moment of inertia grows big. As a result, you cannot turn quickly.

The point of Tenkan move:

1. Stretch your chest and straighten your back.

2. Because a centre of gravity moves to the top when you turn, you need to bend knees and drop a waist. Prevent a body from lifting up.

3. The knee should touch the calf of another foot when cross the feet.

4. Don't open the arms to left or right.

5. Turn a face to the turning direction quickly.

There are Tenkan, Tenkai, Tenshin, Ayumi-ashi, Tsugi-ashi, etc. in the footwork. These are simple action but let's practice firmly with the details.

Thank you for reading.

転換 - 慣性モーメントを理解する 




1. 胸を張って背筋をまっすぐにする。

2. 回転運動をすると重心が上へと移動するため、軽く膝をまげ腰を落として体が浮き上がるのを防ぐ。

3. 膝はもう一方の足のふくらはぎ(膝の裏側)に触るように足を交差させる。

4. 腕を左右に広げたまま反転しない。

5. 顔は素早く反転する方向へと向ける。



テーマ : 合気道
ジャンル : スポーツ

#14 The life that was saved by people 皆さんに救われた命


Twelve weeks have passed since I left the hospital. I was worried about my two-time heart surgery, but now I will be able to return to practice in a few weeks. Thank you very much for your encouragement. I won't forget the feelings of gratitude.

In return, I want to tell you my thoughts about the heart surgery. I would be happy if it helps.

1. Physical strength:
I strongly felt that a result of the surgery depends on the amount of your physical strength. If you have the enough physical strength against the surgery, the hospital is able to make a good surgery plan. If you don't have it, your surgery would be postponed repeatedly. I underwent the heart surgery twice in two weeks. It wasn’t a plan, but I was trying to have recovery of physical strength as much as possible during the two weeks. Even if there was no appetite I ate by force, and I practiced walking as much as possible once I became able to walk.

2. Keep positive thinking:
When your body is connected to many tubes in the bed of the hospital, uneasiness and fear will attack you. At such time, I strongly thought that I absolutely return to the Aikido training, and I repeated the magic words “I won't give in” in a quiet voice. Before entering the operating room, my family said to me "see you soon" with a smile. Then, my mind became 100% positive and all fear completely disappeared. I think that there is the method in various ways, but I recommend that you practice the method regularly to keep positive thinking, if possible.

3. Deep breathing and relax:
When you undergo heart surgery, your rib cage is spread open and the heart and lung are stopped. Blood is detoured through a heart-lung machine. After the surgery, it is necessary for you to expand the lung again. If you fail to this, a part of your lungs wouldn't be restored. You may have a strong pain, but please do your best. It is scientifically proved that all things including a human are formed by energy. Take a deep breath and feel expansion of energy. Then you can be relaxed.

Economists and school teachers often tell you that you should look ahead to the far-off future. But, I think people's minds are different. The best way to get rid of fear is to make purpose of the near future rather than the far-off future, and to realize happiness in your hands. If you have an experience of the long night in the cold hospital, you know it.




1. 体力をつけること

2. ポジティブな考えで心を満たすこと

3. 深呼吸の有益さ



テーマ : 合気道
ジャンル : スポーツ

#13 Refractory Period 神経細胞の不応期


When the brain catches two recognitions, the prefrontal area is panicked and a nerve system is incapable of responding to stimulation. This conflict requires extra processing time (reaction time) for the brain to resolve, and the movement of the body stops suddenly when it really happens.

This reaction of the brain is called “refractory period”.

Refractory period in brain is a period during which a nerve or muscle is incapable of responding to stimulation, especially immediately following a previous stimulation.

In the martial arts, there are a lot of techniques using the refractory period. As soon as the opponent takes an action of attack, you make a reaction which is different from the prediction of the opponent. Your reaction will stop the movement of the opponent, and you will be able to take next move before the opponent responds.

In another example, if the predicted resistance disappears suddenly, the brain cannot respond immediately. You feel the illusion as if the arm of the opponent you grabbed suddenly became a sponge.

If you practice by solely relying on the feelings, sometimes you are unable to find the way how to make progress. In such cases, training with knowledge will help you.

Thank you for reading.

[ 神経細胞の活動電位が発生しない不応期 ]

脳が2つの異なる認識を続けて捉えると、前頭領域がパニックになり神経システムが刺激に応答できなくなります。 この障害は、脳が立て続けに起こった情報を処理するのに通常よりも長めの処理時間を必要とすることで発生します。また、実際に起こると身体の動きが突然停止します。



武道では、神経細胞の不応期を利用した技が多くあります。 相手が攻撃を仕掛けてきた瞬間に、相手の予測を裏切る反応をするようにしています。予想外な反応をすることで 相手の動きが瞬間的に止まり、再び反応する前に次の動きを繰り出すことができます。




テーマ : 合気道
ジャンル : スポーツ

#12 Nuki-waza  抜き技


The first step of understanding of the Aikido is to learn the method of draining of strength.

For example, if you put your hand at the corner of the desk and practice "Taisabaki" body movements, you naturally take a step and move a centre of the body to the corner of the desk without any force. You won't pull a heavy desk towards yourself, not even try it.

However, when the hand is grabbed by somebody, you reflexively pull or push the hand and try to move the opponent. That is just forced behaviour.

Once your hand is grabbed, please relax a shoulder and an arm instantly. When you instantly extract tension from the arm, the opponent also has a phenomenon that the force will fall out for 0.7 seconds.

At that moment, you can turn the hip and do "Taisabaki" body move without any force. If you practice carefully, beginners can experience this phenomenon too.

Nuki-waza” is the technique using the refractory period in brain. So, don’t be afraid of relaxing the grabbed arm.

You can see a reason why "Katatetori Kokyu-ho” (one handed standing throw) is always the first technique to learn.

Before practicing other techniques, it's better to understand the way of "Nuki-waza".

Thank you for reading.

Related article: Refractory Period

[ 抜き技と脱力の使い方 ]





抜き技は、リフラクトリーピリオド 「不応期」 という脳内で起きる現象を利用しています。ですから、つかまれた手と腕から一気に力を抜くことを怖がらないようにして下さい。



関連記事: 神経細胞の不応期

テーマ : 合気道
ジャンル : スポーツ

#11 Irimi-nage 入身投げ


When you drop the opponent's body down, his body often drift away from you due to the centrifugal force. If that happens, it’s difficult to draw his moves to your centreline.

The important point of Irimi-nage is to catch a head of the opponent on the shoulder naturally. We must avoid pulling the opponent by force.

When you drop the opponent at your feet, lead the opponent to the position that you can overlook his head from just above. If you don’t, the opponent moves in a direction away from your centreline.

When the opponent stood up, his head must come to the position of your shoulder naturally.
Thanks for reading.







テーマ : 合気道
ジャンル : スポーツ



初心者にも分かりやすく、理論的に基礎知識を説明します。なんとなく他人の動きを真似るのではなく、普段から考える力を育てていくことを目的としています。In this blog, I explain the basics in a theoretical way that is easy to understand for beginners. The aim is to help you to develop your ability to think, not to copy the movements somehow. Aikido is not magic. I will explain things that are not so clear, such as Ki and O-Sensei's philosophy.