Robert M Watson Jr
Do the twist but do not move the upper arm and as the radius and ulna twist the hand moves ~1/2 inch from the wall. Does this still illustrate your point without the need to include the shoulder?
Yes, but as in my response to Ahmad it is more comprehensive than the arms -- it is the whole body. It seems like a very short actuation, but it sums over the whole length of the structure (to the ground, I suppose
) as long as there are no kinks or discontinuities. Kinks or discontinuities create points of incipient collapse. Those are often compensated by actuating a counter-leverage to stablize, which creates adverse shear, which creates the need for more counter- leverage -- well, you get the picture. Trick is to compensate by the same mechanism and NOT to let leverage come into play. Most days, most ways I get it -- but then I'll get caught out in the odd point ...
And dynamically the length of actuation is not the key -- but the reflexive sharpness and, even more critically, the sensitivity of the more guided applications of the action, Since it is tactile in sense and in action -- no mind is really involved in doing it, just a feel that is also the action being felt -- and therfore very tightly recursive in neuro-muscular terms.