View Single Post
Old 12-01-2006, 01:32 PM   #317
Erick Mead
Erick Mead's Avatar
Dojo: Big Green Drum (W. Florida Aikikai)
Location: West Florida
Join Date: Jun 2005
Posts: 2,616
Re: Aikido: The learning of natural movement

Mike Sigman wrote:
... the basic ideas can be conveyed with the ideas of "force vectors" ('jin', BTW, can also be translated as "force vector") and mental sourcing.
That is better. And this is how I have understood what you are talking about. I get your position, and I'll explain why it is right as far as it goes and why it cannot be applied to address the problems that concern me.

I get, and have always gotten, the points you have made about how this functions in jin terms, and my own conception of it in mechanical terms. I can do many of the things you represent as jin manipulation in just this way, understood mechanically. I have no problem generalizing the mechnical description of it in common terms. I just wanted your mechnical description for comparison. I would still like to hear your description of the manner of propagation or conversion of those vectors from input to output, if I have assessed your position incorrectly below.

We continue to talk past one another, nonetheless, because you all seem to equate these uses of kokyu and ki to their use according to the principles of aiki or aikido, as O Sensei developed it. And that just is not so.

As I was saying before, we are dancing around a category argument. Just because what you are doing is an exercise of kokyu and ki (or jin) -- does not mean, ipso facto, that it is sound as a desciption, mechnically or otherwise, of aikido or the aiki principles by which techniques function, even though they may incorporate some of the kokyu (jin) skills you are training in. This is so even if Daito-ryu or Angier Sensei teach related techniques from their branches of the jujutsu arts that do function in that way...

In that context, the kokyu practice you are illustrating with force vectors has a great deal of relevance, which I have never disputed. It is channeling the reaction of the ground from joint to joint according to the middle third rule, as an catenary (or inverted catenary) profile across linkages.

It would thus use, as you say, the inherent material tension strength or "spring" potential of the ligatures to constrain the forces ( like a hanging cable or catenary arch) within the equilibrated tension sheath of the joint connections, and thus guide the ground reaction directly back at the input vector - thus avoiding any force couple rotation at the point of contact, and keeping any mechanism (rotating hinge) from forming between the two bodies.
Cady Goldfield wrote:
Michael McCaslin's basic, simplified overview of structural integrity and conveyance of energy through the bones (Training forum, "Opening the Joints" thread) might be a good starting point for you in understanding some of the fundamentals.
Tohei Shihan supplied a number of ki exercises and related explanations of them for improvement of aikido training. That does not mean that the ki exercises, which do very well in training ki and kokyu skills, are themselves necessarily aikido technique, or that they themselves necessarily apply aikido principles when developing appropriate ki or kokyu skills. I will describe below my mechanical interpretaiton of the "opening the joints" image as the formation of a catenary path.

Weight training and stretching, and dancing for that matter, certainly all improve critical physical elements of the game of basketball and help increase the level of play. They are not basketball. That does not denigrate either weight training, stretching or dancing, each of which have merits in their own right.

Aikido is a particular applicaiton of ki and kokyu. Gravity is the same everywhere, but the uses of it differ markedly. A 747 and the Empire State Building both allow one to reach a height of some 1250 feet, so they are obviously equivalent, neh?

The problem with this as aikido is not with the channeling and intergation of the path of forces toward the center (which are very much part of kokyu and good training), but with the use of the ground reaction from the center by that means.

If O Sensei is to be believed, the practice you describe is certainly training in kokyu (or jin) and certainly ki -- but it is not based on aikido principles. Aikido does work on the basis of the proper shape and control of forces in the manner by which Mike seems to suggests in channelling ground reaction. Aikido just doesn't operate on the basis of ground reaction.

To do so requires there to be in-line resistance at the point of contact to oppose the input force. The rooting, grounding and vectors references seem to strongly suggest that. If you all mean otherwise, please elaborate. Ultimately, as you describe the grounding of forces or channeling the ground reaction -- there must be linearly opposed forces at the point of contact, and thus --- resistance.

In aikido there is no resistance. This statement is the key to the problem and the solution to it. If there were not this direct opposition, there would be a force couple, rotation and mechanism. And if there is rotation then the input force cannot be met with the ground reaction; there can be no ground reaction because there is no longer any direct force path to ground. That is where the aikido comes in, and what it in fact exploits.
Cady Goldfield wrote:
... these things have nothing to do with mystical "secrets," they are technical skills that can be learned. People have varying degrees of talent for learning them, but these biomechanics are within the realm of pretty much any normally-formed human body.
We agree on this.

Aikido technique and the kokyu involved there just isn't a statics ground reaction problem, is it is a dynamic angular momentum problem. There is turning about a center -- many centers, individual joints and tanden, and on more than one axis simultaneously since we have (relatively) flexible connections to work with.

Joints are tension strap-linked mechanisms. Those linkages are mostly all actuated on opposed ligatures (on several axes of different linear input capacities). They all form a number of potential force-couples at a joint. If there is a force couple it has a center of action, there is either a torque or angular momentum there, and it has an vector of orientation.

If there is any offset in the opposing forces at the point of contact (and thus no direct resistance), there is a force couple and a rotation occurs. There is, accordingly, no transmission of the input force linearly in the static middle-third path through the joints toward the ground since that force is being applied to the rotation of the joint couple.

If a torque (vice free rotation) is experienced in the joint, because the force couple is being countered by muscle or tissue tension, then the force is transmitted not linearly through the bone, as with the ahngin chain or stable arch, but by a lever moment from one joint to the next, which is created by the resistance of each joint to the applied lever moment.

If the joint maintains the catenary (or parabolic) path by means of the middle third rule (which you are training for in "opening the joints") then it produces no leverage or counterforce but merely communicates the free rotation along a progessively larger moment arm. That means more inertia for the input force to have to rotate, or conversely it diminishes the effective moment of the input force couple at the other end of the moment arm it is rotating.

Essentially, this uses the integration of the individual joint moments according to the training you are talking about but by moment conversion, not ground reaction -- distributing the applied moment to a progressively larger inverse moment arm on the other side of the force couple -- which it has to rotate. It is working towards the "whole-body" tanden-centered motion that requires but a very small out of plane moment to radically displace the incoming moment along that very large whole-body moment arm, and in a plane that the input force couple does not act on at all.

The final reversal of the moment arm occurs in the change of eccentricity from one hip to the other, either in the uchi or soto (tanemura-ha /shimamura- ha) motion of the technique. Thus the input moment is effectively reduced to nothing at the tanden of the intended victim, and reversed to transmit the moment back to the attacker from a different axis without any resistance developing anywhere, and without any resistance by the attacker because his force is necessarily occupied elsewhere.

Imagine a giant sphere in the bottom of a large bowl. If you try to push it straight out of the center it will freely rotate and roll up the side of the bowl as far the input force allows up the slope of the bowl. But if in the course of that push an internal mass damper inside the sphere shifts just slighty off-center, the new center of rotation causes the sphere to rotate laterally one way or the other as well as vertically and basically deliver all the pushing power back onto the pusher from the side, where he has no resistance, as it rolls around and spirals back into him toward the lowest point of potential energy, but all the while it is still rolling away from his push and not resisting at all.
Mike Sigman wrote:
... sort of like riding a bicycle.... trying to describe how to do it on paper is futile, even though it can be taught fairly easily.
By definition, no forces involved in the couple operate in the plane of the torque or angular momentum vector. The angular momentum of a coupled rotation creates inertia about this axis vector that resists displacement in the plane of the axis vector -- even though no active forces operate their directly.

That is why a bike does not fall down and can be steered without hands, by the way. And that fact -- that riding bike can be learned easily says there is a fundamental relationship between the stability systems involved in both bicyclic and bipedal motion.

There is something exceedingly useful to be learned there about how ikkyo works , for instance, in communicating displacements through joint articulations without direct forces (resistance) being employed at any point -- even while standing (like a top) on the ball of one foot, a la Shioda's conception of chushin ryoku and the importance of the big toe as the axis of the chushin power. The mechanical "power" on that axis of the body is either applied torque or angular momentum about the tanden.
Mike Sigman wrote:
To compound the problem, you want some form of mathematical modelling so that we can discuss this on some form of elitist plane. ... this is not the "let's impress 'em with mathematics" forum.
That's not what I'm talking about, nor is it necessary to get into diffy-q or higher algebra. What I have done here is the classical narrative approach to these types of mechanics. It is essentially a narrative form of dynamic geometry, more than anything. To see how that tradition has been revived in the feild of plastic mechanics and architectural engineering. read Jacques Heyman's "The Stone Skeleton" or "The Masonry Arch" That precise analysis according to Coulomb's method addresses what you are doing in channeleing ground reactions through an inverted catenary path formed at each joint successively. It has a definite shape, equivalent to tegatana, which you can manipulate mentally.

Heyman's approach, extended to the mechanisms of collapse, allows essentially non-linear moments and plastic mechanics to be assessed within useful confidence limits in situations where FEM or differential analysis cannot easily, if at all, generate instantaneous solutions across the same range.


Erick Mead
  Reply With Quote