Your belly button is important!
Twisting the waist against the hips and releasing it is the biggest power source we have in the martial arts, but far too few practitioners are able to use it.
When twisting the waist most practitioners turn either the hips or shoulders instead, either collapsing the knees and/or leaving the waist motionless. Kata like Naihanchi and exercises like Chan Si Jing in Tai Chi are structured to learn this skill.
If you adopt an internally rotated stance like Naihanchi Dachi in Karate or Ma Bu in Tai Chi fixing the hips to face forward and then twist the waist against the hips so you end up with your belly button facing the corner and your hips to the front you will feel the powerful twisting power build up in your waist ready to be released.
Wado Ryu founder Hirinori Ohtsuka described it as ‘firing a bow and arrow whilst on horseback’ when describing its use in Naihanchi. In my experience karateka tend to focus on the hips and the waist is usually frozen stiff.
The psoas muscles are the biggest and most powerful muscles in the body, connected from the diaphragm to the inside of the upper thigh and when you turn your belly button to the corner with the hips front facing and then release the twist, you will feel them stimulate store and then release energy, lending power to your arms and hands and most importantly sending energy right through the body engendering good health and vitality.

