The “opening and closing” of the armpit is managed by using kyokotsu or sternum in the correct way. This is necessary to perform an efficient movement when aiming for a target.
Using kyokotsu and “koshi” in a correct way (koshi-mawari) is the key to send the power of the base (earth) through the arms into the opponent. About koshi mawari, you can consult: The influence of Chidori ashi.
Controlling “kyokotsu” or “sternum”
Controlling kyokotsu or sternum is explained by Akira Hino in his book: Don’t Think, Listen to the Body.
The picture on the left is a sort of simplification of the mechanism. It has also an influence on the utilization of the koshi.
When the sternum is moving, the spine is also moving. This creates a pelvic tilt.
The pelvic tilt has to be the result of a full body movement. Just doing a pelvic tilt has no influence on the movement of the upper body when there is no connection between upper and lower body. Also just doing a sternum movement has no effect on the lower body if there is tension around the spine.
Straight line and koshi mawari
Directing for the target is a simple action with a lot of difficulties. The skill of opening and closing the armpit has to be entirely understood, mentally and physically.
When there is no control of the armpit, there is a probability of missing the target.
To resume, we can point out:
- Rotation of the torso
- Extending the arm in a straight line aiming at the target.
- Opening and closing of the armpit.
Using a jo to perform taijū no dendō and koshi-mawari
During “corona” time it is necessary in a partner exercise to maintain distance, especially when you are practicing with someone not belonging to your nearest social contacts. The “jo” or medium range stick is the ideal tool to make contact and still maintaining a distance.
This video clip demonstrates taijū no dendō and koshi-mawari with the help of a jo or a medium range stick. It gives the opportunity to feel how partner is using power to push you back. There are some points to take into account on both sides of the stick.
How to push the stick forward?
Starting from a “chidori ashi” posture with the hand holding the stick near the body. Move the center line forward until you feel pressure in the ball of the front foot. Start turning the body while extending the arm forward.
How to receive the incoming stick?
Chidori ashi posture. Move the center line back until you feel pressure on the heel of the back foot. Start turning the body to absorb the power into the floor.
Relationship with compatible martial arts
A clear relationship with Jodo Kata “Suigetsu”. The straight line and koshi-mawari is only successful if there is a control of the armpit and the extended arm holding the stick.
Remark also the straight center line and the advice not to bend the body and arm.
There are of course more examples about opening and closing armpit in relationship with koshi mawari. Simply for the purpose to keep this post compact, my advice to find out by yourself and find similarities in other martial arts.
Study Group Tomiki Aikido 