Interesting posts! After reading them, re-reading my previous one, and teaching a few classes, I had some additional thoughts I wanted to share about (1) helpful exercises, (2) holding the head up, and (3) how I have recently used the Shen/spirit in push hands and in the form.
To get a feel for this, we have an exercise I have described before. You hold an arm in the typical Ward Off shape and have your partner rapidly and rhythmically push on it, like a boat bobby in the water, but with a faster cadence. You want to respond like water, yielding only to as much force as is felt and returning to the original position as the force is withdrawn.
I think this exercise accurately translates the quality of muscle and tendon action we want; however, it does not really describe tactically how to use these qualities. In our way of thinking, if you try only to absorb the energy of a push or pull, you will always reach a limit to what you can absorb and so must do more than just this to succeed. The exercise above gives an idea of the principle you use in responding, but does not tell you what tactics to use to supplement it. To learn the tactics, you need to study applications and counters.
In doing applications and counters, you will generally go through those extremes of light and heavy, but not really during normal circling drills or while doing form, where the Yin/Yang extremes are much narrower or even hardly visible from outside. I find that, as a result of this difference, some people do not quite know how to translate these feelings into their normal practice.
You can also test whether you are too limp or too stiff using another similar exercise. If your partner can give a sudden moderate push to your arm and simultaneously affect your torso and balance, you are too stiff. If your partner, on the other hand, can immediately collapse your arm and reach your torso, you are too limp. This exercise is not about "grounding" force as some teachers talk about, but rather about the quality of your muscles and tendons. Water does not ground itself or actively neutralize incoming force. You want all your joints to have this quality as you do the form.
When I begin to teach moving push hands, I often teach a variation of the above exercise, and some of my students and friends seem to react more clearly to the competitive aspect it offers. This exercise works even with partners who know little or no Tai Chi.
Stand with your partner so that you both have your right arms bent in about a ¾ circle, like you normally use for the Cross Hands Posture or at the beginning of our vertical circling. Touch the back of your right wrists to each other along your joint center line with your forearms angled at about 45 degrees from vertical. Adjust the distances of your stances if necessary to maintain the right arm shape. Then, each of you should touch your left palm to your partner’s right elbow. Adjust your pressure at the three contact points so that your partner cannot easily disengage at any of the three and move to strike you without having the path of the strike altered. These means that you must not merely touch, but must give light pressure. Now repeat the same process, but end up by lifting your right leg off the ground and standing only on your left leg, keeping it straight, but not locked. Adjust your distance, if necessary, so that both of you are standing upright and feel comfortable.
If you feel your partner’s structure is too stiff, or merely to test it, give it a sudden pulse of energy (i.e., Fajin) without changing any of the contact points. If the partner loses balance and has to put the other foot down, they were too stiff. Even if you can shake your partner’s torso or affect its position, he or she is still too stiff and is giving you too much control of his or her empty and full. As another option, you can simply withdraw your pressure suddenly and see if your partner falls forward toward you.
If you feel your partner’s structure is too limp, see if you can push all the way to their torso and make them lose balance. These means you have to be standing close enough to make this possible. In this scenario the person receiving the push should be able to simply redirect it to the side without losing balance or setting the other foot down and without the pushing energy reaching the torso. If you just try to receive the push in your torso and elbow, you cannot avoid being pushed over or having to gyrate so much that you will lose your balance and have to put your right foot on the ground.
What this exercise shows is that if you are too stiff and too limp, you give your opponent some control over your torsom your stepping, and you yourself.
I do not want to give the impression that you should never allow the opponent’s hands to reach your torso or to collapse your arms. This is indeed part of the exercises I just described, but is not true for our Tai Chi in general. In fact, our standard elbow application requires that you figure out how to guide the opponent into a push against your torso and even pin your opponent’s hand against your torso. Other applications require similar motions. Even though you do this, you do it in a way that allows your opponent to touch your torso or squeeze your wrist against your torso, but not to send energy there. You have to begin to understand full and empty to do it right. Although applications and counters are a major area of our study, they are in a way not fundamentally what we study. What we really study is energy and the diversity of its full and empty.
I also seem to be discussing only “pushing” energy and not “pulling” energy; however, as I understand it, Peng energy has only to do with different amounts of expansion, not really with contracting. In this sense, Peng can only push out from the center and cannot pull in toward it. This is similar to how water only floats objects and does not sink them. Boats sink because gravity pulls them down and the water fails to float them enough to counteract the force. This lack of “pulling” does not mean, however, that Peng and its derived energies are limited in direction, just as water can bob you up and down or from side to side, or a wave at the beach can knock you downward, or the current of a riptide can carry you underwater, even though water has no hands to pull you anywhere. Of our eight “standard” applications, at least half (the Ward Off one included) involve the opponent ending up behind you as if "pulled," even though in all cases you end up sending energy away from your center and not inward towards it.
I do use one or two overt pulling exercises to teach about how to manage full and empty between the legs and arms and how the outward aspect of the energy needs to come from down to up, but they have a different purpose from what I describe above.
As for keeping the head up as prescribed by the first of the Ten Essentials, I can add a few thoughts to what has already been said.
First, there is an external and internal part to this requirement. The external deals with the placement of the head and its effect on the body shape. The internal part deals with the use of the Shen/spirit and its effect on the Qi. These two also affect each other.
What is required is often described as pulling the head up as if suspended from above. This is a process that results in a dynamic that is fundamentally different from just "keeping the head or neck straight," regardless of the level of force used.
From an external point of view, the head is a very heavy part of the body, and you need to keep it aligned so that its weight does not put undue strain on the alignment of your muscles and skew the energy dynamic they manifest.
Pulling your head up allows you to let your shoulders sink properly, which in turn allows your elbows to droop. If you let your head bend forward, your shoulders will tend to come up. This contrasting feeling is a major thing I look for in trying to pull the head up.
You pull your head up, but do not bend it backward. Pulling it up allows you to feel your chest sink in and your upper back be pulled up. Bending your head backward does the opposite: puffing up the chest and depressing the upper back. Again, I try to feel this contrast.
Bending your head forward will also begin to limit the ability of your spine to store energy like a bow. The Peng in your spine comes from your tendency to pull your head up. The movement characteristics of our flavor of Tai Chi do not show much external bending of the spine, but internally, our spine does indeed change.
From an internal perspective, bending your head forward begins to compress your lungs and obstruct your breathing, affecting your Qi. In fact, “Sinking the shoulders and letting the elbows droop” and “Enfolding the chest and plucking out the upper back” both have an aspect of encouraging the Qi to sink down the front of the body and collect in the Dantian. For similar reasons, we do not want to pull the tail bone too far forward or resort to intentionally clenching the abdominal muscles. Both of these actions tend to squeeze out the Qi or limit what can be stored.
Raising your Shen/spirit and keeping it calm also helps you sink your Qi to the Dantian. Up must compensate for down; therefore as your Qi sinks down the front of the body into the Dantian, the Shen/spirit needs to rise up the back to the crown of the head. Qi tends to rise, especially with activity; and therefore keeping calm allows it to stay down better.
Your spirit and/or mood also have a relationship with how you tend to hold your body. Depression inside tends to manifest as depression outside, and vice versa. Energy inside tends to manifest as energy outside, and vice versa. Therefore, you also want to try to use your mood to raise your spirit directly in order to raise the level of the energy you can manifest externally.
As for recent experiences, I can describe two incidents with my students.
In one case, a student was having difficulty doing our standard Rollback application, which comes out of a vertical circle. As I experienced the student’s energy, I judged that I felt more of a pull than a push and tried to convey this correction. It didn’t help. I then decided to try an “internal” correction, since I noticed that the student’s eyes were leading the application in a way that screamed “pull” to me. After accepting the correction, the student again failed to execute the technique properly, but I noticed that even though the gaze was now correct, the head angle was still wrong and still seemed to scream “pull.” In other words, “Internal and external were not united,” as required. After a few more tries, the student finally managed to make eyes, head angle, and spirit agree, and I felt the energy spring out as I was sent flying out of control like a rag doll.
A place in the form to look for similar problems is at the end of Single Whip. Because of our body position, which is open about 60-70 degrees to the right, it can be somewhat uncomfortable to turn the head fully to the left. Our requirement is that the gaze end up looking through the Tiger’s Mouth in the left hand and that the face itself be pointing directly in that same direction. Without this, it is hard to generate the correct energy with the final technique in the left hand.
Another student was also having trouble with the Rollback application. My requirement is often that the student be able to generate enough force to be able to slam me around, even if they don’t actually do it. This student seemed to have the externals fairly correct, but still I could feel that the Shen/spirit was off and that the application did not have enough power. What I related the problem to was the requirement “to use stillness to control movement” or “to find stillness in movement.” This is a matter of Shen/spirit, according to my understanding. In the simplified dialog I often use in class, I usually describe this matter of theory as the requirement not to feel that you are moving somewhere to do something that will affect the opponent, but rather to feel that you stay comfortable where you are and make the opponent move instead. As the student made a repeat attempt to do Rollback, I began to make my usual explanation of this principle. The student, who is used to my blathering on, understood immediately what I was talking about, made the correction in mid speech, and sent me flying away with a big grin as I had to shut up and make sure that I could safely come to a stop before encountering a wall, stray furniture, or the not-too-welcoming floor. What I felt this time was that the student stayed in place and that all the energy moved into me to set me flying.
Places to look in the form for this problem include whenever the hands are executing a push or an open-hand strike. The head and the spirit need to feel anchored or even almost as if they are moving away from the striking hand, just as the hand and fingers releasing a bowstring stay in place or even move away from an arrow that is shot. The general that is the spirit closely observes and assesses the effect of the attack and the flow of battle, but does not rush forward to take part.
Again a long post. Trying to describe physical things accurately and unambiguously takes a lot of words. Describing theory effectively seems to take even more. In any case, I hope what I wrote was correct, clear, and helpful.