The katana is such a dangerous weapon that it could not even be handed out for to look at it. Even a check on the sharpness of the blade would lead to serious injury. So uncontrolled swinging of the sword is enough for a deadly stroke, but it is not enough for correct Iaido.
Form follows function
A special feature of the Japanese sword is its curved shape. I don’t want to point out the origin of this, but the correct use of the blade. Imagine if you spontaneously had to take up a weapon, you would grab the next best rough stick to defend yourself. The stick increases the range of an attack, increases the force of a blow due to the leverage effect and keeps you at the other end of the danger side.
A katana is not a stick
Using a Japanese sword like a (straight) stick will not work properly. It is always enough to injure an opponent (see above). You hit something with a stick, you don’t cut through something like a sword. Tenouchi requires the correct guidance of a curved blade. This turns a strike into a real cut. Both hands are turned inwards during the pulling through and thus the ulna and spoke of the arms are turned.
Perfect sword control
This has several effects: By turning the hands in, the force of the arms on the handle is reduced, which stabilizes the blade guide. At the end of a cut, the hands sit slightly above the handle and it is easier to stop the sword in the end position. This allows the shoulder to relax. Ultimately, for each position of the cutting sword, the optimal position is achieved in relation to the cutting edge and the force applied.
Certain version of Tenouchi
Performing a good tenouchi takes a lot of practice time and results in constant improvement over time. First of all, it is all about changing the position of the handle, then the arm position is improved. The shoulders relax, the hands become loose. Then there is the question of the right time for tenouchi use. A good brand is: at eye level at the latest. Tenouchi can also be started overhead – but it is more difficult because you have to feel it.
Use the whole body
Then, at the latest, one wonders when this starting point has been reached. Now the high school of tenouchi begins. The entire body movement in the vertical flow of force is behind the Tenouchi and finally the question of the right moment during a Kata. The whole body is stronger than just the arms, so the swinging of the sword is easier and looks light and relaxed. It is clear that the head has to play along. With this, the correct preparation of a tenouchi finally takes place from there.
Conclusion
In the end, the good ›twist of the handle‹ was not the beginning of a better technique, but the result of your efforts.