John Riggs wrote:
An observation I have held for some time is that the arm position and vectors appear to be similar to the tetrahedron shape used in the geodesic dome concept-a strong structure for dissipating energy. This appears to ground the forces in my observation. Maybe Bucky was on to something.
That's a great observation and I've heard a number of people suggest that relationship where the body is a tensegrity structure.
If you want to look at it like that, it's not a bad example and *none* of the simple models of how this stuff works are very complete anyway. So why not use it in this discussion of baseline skills? Maybe it will lead somewhere.
The essence of a geodesic dome or a "tensegrity" structure is that it represents a number of forces that balance such that all forces involved are satisfied. There is actually a saying in Tai Chi about the body being balanced in all directions (same as our 6-directions comments) so that if a force attempts to offset a body in this kind of balance, it will automatically (take that with a grain of salt... it's a trained response) move to rebalance in all directions and throw the opponent. I.e., the opponent throws himself in his attempt to disrupt a stable tensegrity structure.
A geodesic dome is more or less spherical, which makes its ability to satisfy all forces reasonably straightforward. There are tensions across the various structural members and the panels holding the structural members together. If you start pulling out panels and struts from the overall spherical structure, you have to compensate by adjusting your tensions... i.e., the number of forces, the directions of the forces, and the magnitude of the forces.
A human figure can be thought of as a set of struts (the bones in the skeletal structure) that is cohesive if you allow the "tensions" or the "connectivity" in conjunction with the muscles to hold everything together as a whole. Most views of the body as a structure look at the skeleton and muscles as the main elements of the structure, but if you change the perspective so that it is the skeleton, muscles, AND the fascial layers that comprise the structure, you have a more complete picture. Then when you factor in the idea that the body is capable of micro-adjustments that can change the direction and magnitude of forces within the structure, you're closer to seeing what's going on.
In the two videos, both Ueshiba and Sum are taking incoming forces against a tensegrity structure, with a focus of the forces going to the base of the structure. Sum is younger and fitter and has worked more on the structure (and a couple of very cute mechanical tricks that augment his reaction)... you can see that there is more "tension" and coherence to his structure, which greatly increases his ability to bounce his uke away.
BTW.... think how much easier it is to do a forward roll with a nice tensegrity structure, rather than just strong muscles or worse, a semi-limp body.