Regarding your message:
“And when that happens pay attention to the nape of your neck, along your spine downward to the bottom of your shoulder blades.
When I perform this movement, I feel my chest and arms "open" in that they pull further away from each other, my back "close" in that my shoulder blades come closer together and a distinct, to me unmistakable, feeling of "opening" along my neck and spine at the same time.”
It’s great to see this. I think my whole objective in starting this thread was to explore the implications of T.Y. Pang’s highlighting of the feeling in this area of the spine, to pay attention to it and try to understand its importance. You’re clearly doing that. There have been lots of other good contributions to the discussion.
Some years back (2005), we had a “what have you been working on in your form” discussion thread. At the time, I was working in particular on “containing the chest” (han xiong). Here’s what I wrote at the time:
“I thought I had a fairly good grasp of the practice, but I’ve discovered that I was only really aware of it in certain postures. I’ve been trying to integrate it into the whole form, so that I focus on ‘containing the chest’ in movement and transition rather than in ending postures only. I’m finding that this focus is helping me to feel more of a connection between my two arms, and a greater sense of arm movement being integrated with my torso. I’ve also been noticing a difference in the way the more extended and stretched-out postures feel as a result of containing the chest. Overall, it seems to enhance the focus on the torso as opposed to the limbs, and on core movement as opposed to peripheral movement. It also occurs to me that the notion of containing the chest is just another aspect of the all important requirement to fangsong.”
I also dug up an old translation I did of Gu Liuxin’s explanation of hanxiong babei, from Taijiquan Shu (The Art of Taijiquan), from his section on the back and spine that I think relates to our discussion here, as he mentions the spinal vertebra between the shoulders:
“Contain the chest (hanxiong)” and “raise the back (babei)” are interconnected. When one is able to contain the chest, then one is able to raise the back. “Raising the back” is when the chest is contained slightly in, the musculature of the back loosen and sink downward (wang xia song chen), and the vertebra between the two shoulders (the spinal vertebra, the third fundamental beneath the neck), have an upward rising stimulus and a slight leading or drawing toward the rearward upward direction—it cannot simply pull toward the rear. In this manner, the muscles of the back have a certain elongative tension and springiness, the skin has a sensation of being drawn up. Since the spine, shoulders and arms are mutually linked, therefore the taijiquan treatise states: “the strength issues from the spine.” In actuality, it is the musculature of the shoulders and back working together in the application of strength, rather than one group of muscles working independently in the application of force.
—Gu Liuxin, Taijiquan Shu, p. 35