Skipping straight to the end:
...Glad you found the post informative.
Tim, this is a landmark thread that will go up alongside the Baseline Skills thread as an IT reference. But this one gets down to nuts and bolts, more--or gears and pivots?
It seems you're describing a system where the feet are "attached" to the ground and the spine is a relatively freely-pivoting shaft on top of the arch between the legs. And right there, you have a sort of double-reel mechanism (right and left psoas muscles) that by alternately tightening and loosening rotate the vertical shaft of the spine. Plus, this area can be tilted forward or back, creating the ability of the center to move circularly in a limited range (limited as long as the feet remain in place). And at the upper part of the vertical shaft, the cross-piece of the shoulder-girdle turns with the turning of the shaft, which is operated by the double psoas reel at the bottom of the shaft (at the top of the arch between the legs). So reeling the psoas of the forward leg turns the spine and brings the rear shoulder forward (in this case, causing the spear to move forward).
So you're talking about thrusting the spear by rotating the vertical shaft with about a 2" diameter. And the rest of the body is not so much pushing the thrust as it is supporting it. And the reason to focus on the lower end is that it's the part that's connected to something--the ground. The shoulder girdle and arms are not connected to anything. But the intention is to bring them into contact with something else and to penetrate or move that other thing. I think the difference in internal and external martial arts comes in right here: in external arts, the power to penetrate or move the "other thing" is in the muscles of the arms and legs. The whole body is involved, of course, and maybe turning or pushing with the hips. But that is very different from rotating the spine, itself, on top of the arch between the legs. In the best external arts, these things will be happening, but they will be incidental and not the driving factors. Internal arts, on the other hand, work somewhat backward to logic: instead of pushing off with the rear foot, you're pulling from the front psoas...
Of course, the feet are "pushing" through all this. All the parts move together and contribute to the cumulative effect on the thing to be penetrated or moved, but it's not the kind of coordinated, even chaining sequential efforts we normally think of for achieving work. So it's not an easy thing to look into, but with this thread, I think you've stepped up a magnitude in the IS world (at least the intellectual side of it, and I hear that your physical ability is more advanced than that).
But now, I have this concern: is that dual reeling of the psoas, for side-to-side turning of the center, combined with the forward and backward tilting of the pelvis, the main way of moving and "rotating" the dantian? Certainly, the turning of the vertical shaft seems exactly consistent with what I understood Dan to be showing. And I probably wouldn't have to be asking this now if I'd watched more of Mike Sigman's IS videos....but there are a lot of muscles in the abdomen and you can exert a lot of them in trying to "rotate" the dantian. And all that can be eliminated if "rotating" the dantian is as simple as that vertical spine rotation combined with tilting the pelvis. That becomes like the little gear at the center of a Rubik's Cube, allowing universal movement (when you add stepping). And when the feet are fixed in place, it allows you to pass the push of the feet into the torso. The trick then is to get that push and the support of the earth all the way out to the hands.
I did the spear thrust as you describe it several times concentrating on the counter-reeling of the psoas muscles before I felt I could turn my attention to the shoulder girdle. And then I realized I had been letting the cross fold inward as I pushed the spear forward: the rear shoulder was coming toward the forward shoulder. When I concentrated on keeping the cross, I felt that the whole spear thrust came from the rotation of the vertical spine and it wanted to draw me into a forward step as in shintaijiku, to continue the forward movement of the spear. But I've just been holding that position with the feet in the original positions and the spear (bo) at the full extension of the thrust. Then I feel that the front of the body is sort of supporting while the skin of the whole back of my body seems to be crawling up and forward. As I hold that position, I try to feel the whole back (pretty easy, the way it feels) and then I think about Bernard's comments about lowering the elbows, rotating them downward, and everything seems to flow out a little more toward the tip of the spear without taking my balance forward. I keep awareness of the pelvis tilting forward, the dropping of the tailbone, trying to feel the rear foot in the front hand and the front foot in the "pushing" hand. And I stand there for a while like that. I'll do that three or four times each, alternating left and right. And I do that three or four times a day, getting someone to push me whenever I can...
I also use a slightly shorter staff which is about twice as heavy as my bo, much of that weight being at one end. I thrust the heavy end out and and stand, feeling the connections. It's very exciting.
After I first started doing the shoulder relaxation thing (246 times, now) I started getting flashes of how Ark stands and how relaxed his shoulders are. But when I started doing these thrusting exercises and felt the activation of the whole back side of the body going up and out, I started understanding something else about the way Ark stands and moves. It does seem like his back (back of the heels, back of the calves, back of the knees, all the way up to the back of his head) is all lifting. Is this what has been referred to as "dragon back"?
Thanks very much. More later.