This is used to describe the stabilization of the body for a solid position by locking the joints in the body (ankles knees and hips) and gripping the floor with the toes ankles, knees and hips, and by gripping the floor with your toes. Chin Kuchi is the concentration or focus of strength and power, by the simultaneous contraction of the muscles in the body at the point of impact that brings karate techniques from a fluid, relaxed stated designed for speed, to a solid, tense state that is designed for strength. The process of “whipping” out a technique, tensing upon impact, and then immediately relaxing again allows a practitioner to achieve maximum power while exerting minimal energy. As well, Chin Kuchi Kakin is the positioning of the body where, when combined, the muscular and skeletal alignment is at its strongest. That is, alignment of the Body is made from the feet, to the knees, to the waist (lower spine), to the shoulders, to the elbows, to the wrist, to the weapon – that is the “snap of the whip.”
This is one of the hardest concepts to grasp in Goju Ryu Keiko. That is, which muscles to use when doing a Tsuki as the best example, it is important to realise that this is where the term Go Ju will make itself clear. As it is necessary to tighten (Go) your joints to get the mass of your arm moving then you must totally relax (Ju) your body and use physics, in other words momentum. At the point of impact, you must than tighten all your body joints and have correct spinal alignment to get the most out of your punch.
There are many training practices in the Goju Ryu repertoire but the best examples are Sanchin Kata and Makiwara (巻藁Striking Post). On the Makiwara, you practice to achieve Chin Kuchi Kakin. The post allows you to develop the correct posturing; tightening and relaxing; and then tightening on impact and releasing immediately.