So lately I have been struggling to integrate a couple of mind-'sploding (non-aikido) and possibly conflicting influences on my training. Struggling in the sense that the result is going to define the entire character of my training for the foreseeable future. In the attempt to fit square-peg and round-hole together, a long and rambling train of thought crossed my mind that I am curious if it makes sense, doesn't, or lines up with other peoples' training experience. If you can stomach reading the whole thing, please feel free to shoot down any of it.
It's easiest to show the idea through a few very badly drawn stick figures. Heavy use of your imagination is required to compensate for my lack of artistic talent. Ideally it represents an alternate 2D universe version of me. There is absolutely no engineering or physics rigor in what follows, just bad subjective argument, so please forgive me in advance.
This distinguished stick figure has only one arm and one leg (shown in black) which can only bend in any way at the points they attached to the spine (shown in green). The spine, however, is allowed to flex. Now imagine that I am actually facing to the left side of the image (towards the blue arrow), so my arm is extended out in front, and my leg slightly extended behind me. This is in no way meant to reflect all the degrees of freedom of my body (hopefully) and is very very simplified... Remember: imagination.
The blue arrow shows some force pushing forward against the arm. The red arrows show where I actually feel stress/struggle trying to resist and would ultimately deform me in vaguely those directions.
This stick figure also coincidentally shows how, in all my aikido career, I might have grossly organized myself to ground an incoming force: the spine (what I thought was) straight and vertical as possible.
I would feel my shoulders collapse backwards, my lower back cave in, and my butt push back out. It was later shown to me that even if my spine was actually straight and up, rather than a tense S-curve, it would have been the same. I was just making my spine a giant lever to easily attack my shoulder/hips at those convenient sharp angles.
This only started to make sense to me when I was asked to consider the range of motion of the spine to round out. If the spine is exaggeratedly caved in I feel something like:
Same rough patterns of stress I felt when I tried to keep myself "upright" in aikido. I would usually end up forcing myself into something like that anyway the harder I struggled to keep myself with "good posture".
Or in the opposite direction you end up with:
I'd feel stress bowing me back from below my rib cage while my arm was forced down and hips exaggeratedly tucked in. Also coincidentally, this is where I would end up a lot in aikido trying to compensate for the tendency to cave in.
So what's exaggerated rounding of my spine got to do with trying to keep straight up under that horizontal force? I was always thinking that this motion of the spine was somehow the enemy, only as those extremes to be avoided. The spine was the "central axis", right? That meant something like some infallible pathway between high and low that you could pivot around and was a magical source of power, I guess?
Going back to those nice sharp angles at the shoulder/hip in the first bad stick figure, the structure of the spine was never running into them, just across them, so they have no choice but to give in under heavy load. And once they give in, either the spine was going to go with them eventually if I would struggle to prevent that, or, I thought, to avoid struggling with the incoming force, I'd have to "get off the line" before that happened.
Then I was asked to consider something else:
Pure juice from foot to hand felt as the uniform act of extending throughout, but no stresses going across. Just extending through in a clean arc along the entire body without sharp angles. Extension, I think the word did not mean what I thought it meant.
Rounding could, in actuality, be used not only for evil, but also for good. So the spine has way more mobility to round out than the arm or leg, and here I was all this time trying to pretend it didn't. The entire body was grounding as a continuous unit, in which it didn't really make sense to peg something as an axis, or distinguish it as central for that matter - that didn't really express what was going on. But, okay, this was an idea from an outside source having nothing at all to do with aikido or Japanese MA...
But then it kinda dawned on me: I am not a 2D stick figure and not only can my spine curl and extend, it can torque and other manner of interesting ways at interesting places. So if the spine is being kept nicely vertical, the force applied is horizontal, and it is somehow being grounded... Then either the person has some monstrously strong abs, lower back, shoulder girdle, and hip muscles... Or if they don't, then force is not ideally going through in a line at the shoulder and hips, but is instead being carried a gentler path around, spirally-like, that... axis.
So if there was to be extension, it wasn't to be straight. If there was an axis and it was to be central, it's main job was never to act or ground out along that axis.
The Earth is not flat, it is round. Dots connected. Square peg meet round hole. Check and mate. Put a fork in it. QED. Somehow that made some sense to me, I think. If you have made it this far in my post, your mind is made of stronger stuff than mine.