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.