Re: Discussion last month
Audi: There are several issues that I see in questions raisied in your post. A few comments on the following topics first:
A. preventing the weight of an incoming push from landing on your body
B. pushing against the ground
C. friction against a contact surface
A. preventing the weight of an incoming push from landing on your body
Analogies that I find useful for getting an idea of the feeling involved here include the pendulum/bell clapper analogy and flowing water analogy. You are moving internally, so when an outside force comes into contact with you this force is diverted away from its original course. If this force does not cut off the source of your motion you can continue to move. If this force finds the source of your motion, said force can increase pressure on this source or position.
When touching an accomplished Taiji practitioner one feels like one is putting one's hand into a flowing stream; your hand is pushed along. When a boat is lowered into the stream it moves along with the flow of the water. If the water is not flowing the boat won't go anywhere. The 'flow' is one of waves of muscular activity aka, "jin4". The ability to understand what 'jin4' is, is what the Classics very specifically refer to as the beginning of one's Taiji journey.
The fundamental technique in Yang Style Taiji is to divert half of an incoming force away from your body and keep the other half in your control. This way the incoming force will be ready to 'fall' or miss its target and will be relying on you to maintain balance, but will be unable to land directly upon your "jin4yuan2" (source of jin4). You can also divert all of this off of your body which results in the opponent losing balance or simply being unable to push.
B. pushing against the ground
Having entered into the above state, one does not need to push against the ground with one's feet to 'off balance', 'throw', 'bounce', etc. the opponent away.
Often you see people pushing off the ground directly back at the opponent's force without having first off balanced them. In such a situation not only the force from the opponent being pushed away, but also the pusher's own force is reflected back onto the pusher's body. The result of this is that you completely lose your 'root' and you knock yourself off balance. (you can see this in the NYTaichi video at 0.28 where he shoves the student away so he can go check the video camera; whereas at 0.23 in the same video you see a nice push that uproots the student cleanly and where there appears to be much less pushing against the ground. You can also see the pusher having his push reflected back on himself in this clip:
http://www.searchcentertaichi.com/video1.gif)
One thing that I should clarify is that leg muscles are at all times very active; -loose and engaged- to create the feeling of (Audi's quote of Yang Zhenduo) "mutual constriction"; however, they are not pushing against the ground. The feet are the same as the hands, or other points of contact, with respect to softness and the requirement of "not creating gaps (losing contact) and not increasing pressure" (bu4 diu1 bu4 ding3). A push against the ground will create a state of "increasing pressure" at the point of contact.
The coin bouncing off of the drum is a good analogy in that, like the human body, the drum has a soft part, the head, and a hard part, the shell. To bounce the coin back the coin has to hit the head not the shell. Of course, if the head is not strung tightly across the mouth of the shell the head will lack elasticity. I take the drum shell to be the bones and the drum head to be the muscles and tendons. The Taiji adept is able to "hide" his bones, the 'mechanical parts' or the rigid part of the system. The opponent feels the elasticity of the soft component, but does not feel the rigid structure to which it is attached.
You can 'stack' your bones or line them up end-to-end, joint-by-joint, from the soles of your feet all the way to your hands. You can receive the weight of an external body on the hands and transfer this down, joint-by-joint to the bones in your feet. In this way the weight of the external body rests upon your bones. When you push back against this force the weight of the external body is still upon your bones. You can also take this external weight and put it on your muscles and tendons.
Living in China, the land of intense social drinking, I recently saw an example that relates to this discussion. At a very upscale seafood restaurant where few leave without a stagger, I went to the restroom and saw a row of 'dignitaries' lined up, one next to the other, each in front of his respective urinal with head against the wall above to prop themselves up. They had minimal control of their muscles and had no choice but to 'prop.' When we develop Taiji skills we try to do the extreme opposite of propping ourselves up; against the earth or against an opponent.
C. friction against a contact surface
When pushing or pulling, ideally, after an initial contact and connection, there should be no increase in pressure at the point of contact. There also should be little to no friction manifest on the skin (or garments) of the players at the point of contact. Movement/activity throughout the body as a whole instigate the off-balancing or other controlling effects. In like fashion, the contact of the feet with the ground should manifest -minimal friction- and -minimal pressure- increase (like walking on thin ice).
When done correctly, since players do not feel an increase in pressure and do not feel friction at point(s) of contact, there is often serious disbelief that the effect of the push was real. Since the opponents push was reflected back, there is the feeling of, "I didn't do anything. You just fell back on your own." As a result, players often find it difficult to accept training methods that do not involve increased pressure and friction at points of contact.
Louis:
Here is that same section with pertinent Chinese terms (in Pinyin) added.
With terms like 'rigid bodies', 'workings of a clock', it is clear that he is contrasting a system containing elasticity and fluidity with a system of cogs, gears and chains-what I translated as 'mechanical.'
"Biological transmission of force (sheng1wu4li4) differs from a mechanical system (ji1jian4; parts, workings of a clock, cogs) where force at one end must result in an equal force being applied on the opposite end. The human body is different. It is possible for the opposing force created by the push of the feet against the ground to be completely absorbed (or used up), due to the complex transmission system of the tendons, bones and joints (fu4za2de ji1jian4, gu3ge2, guan1jie2 deng3 sheng1wu4li4 de chuan2di4 xi4tong3). This force thus disappears without a trace (li4 ke3neng2 wan2quan2 bei4 chuan2di4 xi4tong3 suo3 xi1shou1 (xiao1hao4), bian4de wu2ying3 wu2zong1.) This is because the transmission of biological force does not rely on rigid bodies (gang1ti3), but on the contraction of tendons and the rotation of joints."
Jeff