Shin Chook "伸縮"
I've been told I smile too much. What kind of criticism is that? As martial artists, we have a unique perspective on our body. We have the ability to generate an awareness of it unlike most people. Like other athletes (dancers, gymnasts, etc...) we know how to properly move our body to make it efficient in our endeavor. However, we differ in that we have (or should have) a functional knowledge of how to disrupt that movement and effectively destroy the body.
It is this ability that helps us develop true self-discipline. The martial artist can manipulate his/her body as he chooses (or at least, that's the goal... we get better and better with training). And if we can manipulate our body; our mind and emotions are next in line. Hence, martial artists are able (if they so choose) to develop contentedness.
Interestingly, this comes from balance. If the martial art you practice does not employ a balanced curriculum (offensive and defensive, physical and mental, hard and soft, etc..) then you will struggle with this self-discipline. When we talk about Tension and Relaxation we are specifically talking about a balance in the body.
伸 literally means to expand or stretch out; and 縮 literally means to contract or shrink. Clearly, if a technique is too stretched, and unable to contract at the right time with the right amount of tension the technique isn't as effective (and of course the opposite is true). This is very important, because not only does it allow us to employ power at the right time, but it also allows us to preserve energy when it isn't needed.
Funakoshi Gichin thought it was important enough to include it in his Niju Kun (20 Precepts)
十九、力の強弱、体の伸縮、技の緩急を忘るな.Chikara no kyojaku tai no shinshuku waza no kankyu wo wasaru na.Do not forget: the employment of power, the extension or contraction of the body, the swift or leisurely application of technique.
And Hwang Kee uses 伸縮 - 신축 (Shin Chook) specifically in his 8 Key Concepts.
So what is this "swift or leisurely application of technique" that Shin Chook implies? Well, I see it referred to many different ways, but one that seems to come up quite often is "fluid". I see a lot of people that see Dangsoodo and Karate as more rigid, and Soobahkdo and Taiji as more fluid. But is that really the case? When dealing with steels, especially for sword production, we are constantly looking for that perfect balance... a blade hard enough that it won't bend, but soft enough that it won't break. So, for simplicity's sake, I'm going to talk about 2 distinct types of "strength" in steel. You have tensile strength and yield strength. Tensile strength is the amount of deformation the steel can take before it breaks. Yield strength is the amount of stress the steel can withstand before it is permanently deformed.
Our bodies are similar in this regard. When we perform a technique, we must have a balance between Tensile and Yield strength. What this means is "Soft" does NOT automatically correlate with "Fluid". Even though, many people think so. Taiji is not "Soft", but it's balance of tensile and yield strength is good, so it looks fluid. It only looks soft because the techniques are done slowly. But the techniques are far from soft. If I speed up a Taiji technique, it will look like what most people consider a "rigid" martial art like Karate. Same the other way, if I slow down Karate or Dangsoodo, it looks like Taiji. And it does, because there is a good balance between tensile and yield strength in the techniques.
"Soft" does NOT automatically correlate with "Fluid"
But everything comes back to fundamentals, where does power come from? It doesn't come from speed or strength... it comes from stability. So if I perform what looks like a slow, fluid movement, but my body isn't stable (aka, sliding my rear "stable" foot while blocking or punching) then there is no power because there is no stability.
When we practice our martial art, it is incredibly important that we remember to balance our technique. We must remember that too much tensile strength means less yield strength, and too much yield strength means less tensile strength. Using Shin Chook on our martial movements will help us bring this balance, and achieve a TRUE fluid martial practice.