Tai no Shinshuku – Compression and relaxation

                In Mechanical Physics compression is the application of balanced force inwards or Pushing forces to the center of material. This is the opposite of tension or traction, which is the application of balanced outward, or pulling forces. It is also different than shearing forces, which is the direction or displacement of material parallel in two different directions. The compression strength of material and structures is an important consideration in engineering as it defines part of the equation for strength of a specific material.

                For our purposes we will be looking at Compression as a unilateral compressive force, or compression of a material in a single direction as well as the spring effect of materials under a compressive force. My goal is to explain the reaction of the body as we use Tai no Shinshuku or compression and relaxation/extension of the body to generate power.

                When put under pressure any material will suffer some deformation, even if imperceptible, this causes the average relative position of the molecular structures of the item to change. In some cases, this deformation is permanent and in others it is temporary and when the compressive force is removed the reaction force that opposes the compressive force is normally equal and balanced to the initial force. This reaction is similar to the way a spring reacts to force.

                A spring is an elastic object that stores mechanical energy in the form of potential energy. Springs normally refer to a metallic substance that is coiled to crate the sprint, however there are many different kinds of springs. When a spring, with out stiffness variability, is compressed or stretched from its resting position, it exerts an opposing force approximately proportional to its change in length. It can load a great deal of potential energy over the range of the springs surface that can be stored and released as kinetic power.

                To make this more relevant to Karate we have to look at “Torsion springs”. A Torsion spring is a spring that works by twisting it, when it is twisted around its axis it produces a torque force proportional to the tension. This is loading potential energy that can be used to create torsion power around its access once it is released. Think of the twisting in the back leg as you extend your lead hand and prepare to execute a reverse punch, this is using the torsion spring effect as you release the tension in your back leg and straighten it. The turning of the hip and straightening of the back leg simulate this kind of loading and unloading of the leg to generate torsion power.

                Generally, contraction and relaxation or contraction and expansion of the body refers to the compression of a joint using the muscles of the Agonist muscles to create pressure and then using the antagonist muscles to release this compression. However, the muscles are only really able to do two mechanical things; contract and relax. So the contraction and relaxation principle is not about single muscles but more about the joints and muscle groups that work to affect movements in these joints.

                There is a symbiotic relationship between contraction and expansion in the body. If one only contracts the body or uses tension, then the amount of actual force that someone can execute and put towards and attacker will be limited, and the amount of energy used to maintain the tension will deplete the body of energy. In the symbiotic relationship it is often seen that Contraction is the act of storing the energy that the body can create, and expansion is the act of releasing the energy. For good Karate you must be able to use both of these forms of energy storage/expression to make power in your techniques.

               

                When you realize that muscles can basically only contract or expand you start to realize that the idea of a muscle storing energy is a tough sell. Instead you have to look at the muscles in their agonist/antagonist relationship and realize that the power is actually stored in the form of potential energy because of the muscle’s compression/contraction around specific joints. So, the “Potential energy” is in the joint not the muscles. However, the muscles must behave in a specific way to use the spring force or extension to generate greater power.        

                One more thing that has to be stated is that your body should never be sitting in 100% of either state. If you are totally relaxed in the center, then you are totally not ready to move. If you are to tense you limit your speed and the power, you generate will be limited greatly because you will lack the speed/acceleration component of movement. One should feel as if their body is much like a traditional mouse trap, the spring-loaded kind. Your center should always hold a bit of tension but the second that you are called to move you use a total contraction of the body to move to the point of strike, the agonist muscles contract completely and the antagonists relax to allow for complete movement, prior to this however the muscles are use in the opposite way. So, in your ready position the muscles that pull you away from the target are compressed/contract while the muscles that would propel you towards the target are relaxed, then instantaneously you reverse this and propel yourself towards the target with great speed and greater impact force.

                The goal of each Karate practitioner is to develop and improve “Explosive power” in their techniques. To do this you must master the art of relaxation and contraction or expansion and contraction. Dingman Sensei used to say that you should be at 20-30% tension in your torso at all times and the same in your limbs, then when it comes to the movement you should be zipping up to 80-90% tension for a split second then returning to the original tension levels. Keeping the agonist at 30% allows for control and creation of pressure or compression in the muscles. Then you will contract the opposing muscles that move your striking limb towards your opponent.

                 The almost complete “natural” Contraction and relaxation is required to build up speed and in crease the impact force of any technique. This is the nature of contraction and relaxation in Karate.