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12-16-2006, 09:47 AM
Being controversial is fun, but offending people is collateral damage I would prefer to avoid.
This thread is intended to be used to discuss a scientific model of human structure to develop a common language that all might be able to use to understand and discuss basic martial art's concepts.
On a personal level, it is a joy finding someone to argue with. Not all people can argue vigorously, then smile, win lose or draw, and walk away having learned something. That is the real point of 'intellectual argument', or so I was told in school.
Please join in, or ignore as you see fit.
Erick, pushing a chain is a ridiculous idea - and your suggestion that it must 'want' to be pushed is 'Deus ex machina'. I love that you suggest kokyu forces may be compared to the unexpected way a chain behaves when dropped - outstripping gravity merely because of its basic structure. However - you commit an error when you say tensegrity can only describe static structures. If you review the link - http://www.biotensegrity.com/index2.php?option=com_content&task=view&id=16&Itemid=29&pop=1&page=0
you will read under figure 13 that: "Icosahedra are stable even with frictionless hinges and, at the same time, can easily be altered in shape or stiffness merely by shortening or lengthening one or several tension elements. Icosahedra can be linked in an infinite variety of sizes or shapes in a modular or hierarchical pattern with the tension elements, (the muscles, ligaments, and fascia), forming a continuous interconnecting network and with the compression elements, (the bones), suspended within that network (fig. 13)."
You dismissed a gem of an idea with the wave of your hand. For my amusement I'll tell you why I know this about chains - funnest job I ever had was bike mechanic. The parent company came out with a bicycle that could be shifted without pedalling as long as the bicycle was rolling. Ready? Because there was a tensioner at the bottom of the rear wheel gear cluster the only thing that kept the chain always moving independent of the pedals was a slip gear up front where the pedals moved. It spun because the Top of the chain rolled across it - the chain "pushed" the gear. I looked at it and stared until I announced 'won't work'. The boss said, 'get it ready for sale'. What a debacle. As soon as the merest contamination got in the front free wheel it would snag and skip, making the chain jump up and down. One of the bicycles came back folded in half - the chain had locked the back wheel, and since the rider (hospitalized rider) was going down hill, the wheel wrapped the chain and kept pulling until the frame pretzeled. Not fun, but a story I love to tell.
Find another model Erick - you can't push a chain!
12-16-2006, 08:42 PM
After looking deeper into the biotensegrity model from that thread using the icosahedra I think those folks may be onto something.
Makes me want to research the concept even more. The linkages that icosahedra have with other building blocks of life are very interesting and follows a common pattern found in other elements of nature where basic building blocks manifest themselves in more complex structures while still maintaining the definite identifiable pattern of the original element.
As far as the chain concept goes, I don't think the human limbs and muscles operate under the same principles as that of a chain. Sounds more like someone trying to force a theory to fit to something it is not designed for instead of redesigning the theory. The icosahedra concept imho parallels quite nicely how the bones and muscle structures interoperate to create form and function imho.
Just my 2 cents I'm no scientist.
12-17-2006, 12:41 AM
Erick, pushing a chain is a ridiculous idea Go read Heyman's translation of Coulomb's Memoir on Statics (or the orignla if your prefer, but it is French) and then come back and tell me it's nonsense. I assure you it is not. Devilishly sensitive structure, but all compression and no nosense.
I love that you suggest kokyu forces may be compared to the unexpected way a chain behaves when dropped - outstripping gravity merely because of its basic structure. However - you commit an error when you say tensegrity can only describe static structures. If you review the link - http://www.biotensegrity.com/index2.php?option=com_content&task=view&id=16&Itemid=29&pop=1&page=0
I buy it for the spine. Tensegrity does not deal with rotary joints, however. In any event, if I connect together, with rotary joints, several sub elements of tensegrity structures, I still have -- a chain ...
.... you will read under figure 13 that: "Icosahedra are stable even with frictionless hinges and, at the same time, can easily be altered in shape or stiffness merely by shortening or lengthening one or several tension elements. A chain is a linear structure made up of linked sub-elements. The human body is, ipso facto, made up of forms of chain. You need a whole lot more in the way of anatomy to demostrate that mammalian joints possess icosahedral structure. Your article did not even attempt that. It is an interesting concept, but in need of factual support.
And moreover, focussing on the joint behavior does not say anything about the validity of the chain model -- whatever the nature of the joint, steel link, rubber bands, flesh, or EVEN icosahedral complexes -- it is still a form of chain. Chains can be made of many things.
Find another model Erick - you can't push a chain! Says he, oh so certainly! Not a passive one. But an actively stabilized chain - yep, you betcha!
12-17-2006, 10:17 AM
Grrrrr. You're smarter, so I rise to train at your level. ggrrrrr some more.
I stand corrected, and must revise my statement: "Pushing a chain is impractical."
However, before you argue may I suggest a synthesis? I'll keep your chain/kokyu concept, if you allow tensegrity to describe what you are calling 'rotation'. You agree the spine works in tensegrity, but not the appendages - you are cutting the arms and legs off your own arguement! (couldn't resist that).
My joints do not rotate like the monster in star wars iii, they translate somewhat, but do not go all the way around. If I took my icosahedron (six sticks) and broke one in the middle to make a ball and socket joint, I'd have to have other supports around it - so it still was integral to the structure as a whole. The resulting supports might look very much like strings supporting a tentpole indeed, or to the trained eye (not mine) the soft tissues around the shoulder.
But, if we unite tensegrity with your, from my admittedly limited perspective, understanding of the multiplicative forces acting in a chain to describe 'kokyu', we may have something worth thinking about.
12-17-2006, 09:05 PM
I stand corrected, and must revise my statement: "Pushing a chain is impractical." That's what makes kokyu so valuable -- it is hard to push back against an unwilling chain. :p And very few people learn the one and only one way to push like a chain.
However, before you argue may I suggest a synthesis? I'll keep your chain/kokyu concept, if you allow tensegrity to describe what you are calling 'rotation'. You agree the spine works in tensegrity, but not the appendages - you are cutting the arms and legs off your own arguement! (couldn't resist that). Science is also not negotiation. :D The spine is the best biological model for tensegrity.
My joints do not rotate like the monster in star wars iii, they translate somewhat, but do not go all the way around. A matter of degree, not kind. Literally, "degrees of freedom." Wrist has two, elbow has two, (but not the same two as the wrist), the shoulder proper has three degrees of freedom (universal); and the scapula/collar joint has two. Going down -- the hip is also a universal joint (three degrees of freedom). The knee has only one degree of freedom, and the ankle has two proper degrees of freedom but some limited flexure that lets is operate as very limited universal joint.
The resulting supports might look very much like strings supporting a tentpole indeed, or to the trained eye (not mine) the soft tissues around the shoulder. You need the descriptive anatomy to show any icosahedral strutural relationship in any joint.
12-18-2006, 09:04 AM
"degrees of freedom.
A quick question:
Why does the elbow have 2 degrees of freedom, and the knee only one?
12-18-2006, 01:46 PM
only bends one way?
12-18-2006, 04:16 PM
only bends one way?In one plane, but yeah.
12-18-2006, 05:27 PM
No negative no.
Science is also not negotiation. If you are a human being, then negotiation is second to learning to work a nipple as an infant. Scientists argue like children - and we are discussing a model, not doing experimental science - too early for that stage. May I say to you one more word: Hegel.
Heaven's man! Imagine your favorite dog as a child with a chain drooping from his shoulder. Got it? The poor thing would fall over and look at you with baleful eyes - pleading that you would give a more sensible model a chance! Do it for Rover Erick!
You surf. You can tell when there is a sea change. I can see the tide running - not everyone can - at first. You are focused on the bones. See a bigger picture than the bones - look at the tensegrity icosahedron and imagine it strung with rubber bands. If I link several of them - then deform them in a spiral movement - then let go - they spring back. I have just extended my (tensegrity) arm in the rowing exercise.
Your chain hangs limply from my shoulder. Limp is bad Erick, in more ways than one.
12-19-2006, 10:58 AM
I thought these models might help keep things moving.
12-19-2006, 06:51 PM
To show I'm not just playing I read an introduction to static physics. I got spooked reading about 'dynamics' because hydraulics may play a part in how we move, and that physics gets even tougher.
Erick, I assert that in the human body - there is no such thing as 'rotation'. There is only 'translation'. Rotation would be non integral to the structure as a whole. A friend of mine had a compound fracture and the leg 'laid over to the side' of where it was supposed to. That is the rotation in chained joints that you suggest.
In kokyu modelling, when I suggest we merge tensegrity and your chain - I can't help but think of the old gag with the boxing glove on the multiple pivots. The chain multiplication happens within an integral framework. I don't understand the chain analogy fully, but it's not just speed that koky develops - it's power. By merging the models we may have a decent start, and you can keep explaining 'deflection' to me.
12-19-2006, 07:50 PM
That's really interesting. Especially the pelvis and torso models.
Do you notice that in the torso model, there are two "crosses," and upper cross and a lower cross? That would be an upper "tanden" and a lower "tanden."
12-19-2006, 08:13 PM
A quick question:
Why does the elbow have 2 degrees of freedom, and the knee only one?
Pull out your favourite anatomy reference and you will see that the elbow is made up of 2 different types of joints (encapsulated in a common joint capsule) - the humeroulnar joint, which is a uniaxial hinge joint for extension and flexion of the elbow, and the superior radioulnar joint, which is a uniaxial pivot joint for pronation and supination of the forearm.
The knee, OTOH, is a uniaxial hinge joint....
12-20-2006, 05:59 AM
Perhaps Erick is busy.
Traditional physiology sees human structure in traditional terms - load bearing members, and sees our joints in terms of 'box joints', and 'ball joints', and 'gliding joints'. The 'sea change' I am shamelessly begging Erick to have is a paradigm shift. This shift incorporates the 'fascia' that Mike Sigman always mentions.
I am also trying to get Erick to perceive that the 'immovability' and 'translation to ground' that our talented friends mention is easily explained by tensegrity. Buckminster Fuller designed a book case that used tensegrity and was suspended from the ceiling. The more books, the higher the weight, the harder the book case is to push sideways. Can't find a picture right now.
If one pushes ONE member of a tensegrity structure one is pushing ALL members of a tensegrity structure.
A monk might notice a flower and become enlightened - a nerd such as myself, sees unity in diversity in these models, and stops talking for five minutes.
The book Structure of Scientific Revolutions by Thomas S Kuhn is a must read for all scientists and nerds, and describes 'normal science' and 'revolutionary science', and paradigm shifts. Erick, if you don't have a copy pm me your address and I will send you one!
One more thing - the simplest inherently rigid structure is the triangle. If our bones are the 'sticks' in tensegrity and our fascia are the 'strings' - then our body is full of triangles! With this structure I can stand effortlessly - I can load for koshinage almost effortlessly, and a master can act very powerfully and seem to do it without straining - because no strain is required.
12-20-2006, 09:26 AM
I hadn't clued in on the crosses. Talk about hidden in plain sight! What did grab me, though, is the quicktime animation of the pelvis and femurs. There is one movement in particular that looks like a power release. The torso winds and stores, then releases. Too bad the models are so expensive... I think with some tweaking they would be good teaching aids.
12-20-2006, 11:04 AM
Pull out your favourite anatomy reference and you will see ....
If I had a favourite anatomy reference I probably wouldn't have had to ask the question! But after a bit of rummaging around on the internet I get it now. Thanks. :)
12-20-2006, 11:43 AM
No worries about the crosses. I am still a beginner too and so I miss a lot of things.
Yeah that animation is really thought provoking. Recently I saw a newspaper article (no link, b/c the link broke) about a laboratory that has built a model of human walking. You can really see the "sway" in how a normal person walks, and this is similar to the walking you see in the torso/pelvis model.
Definitely I think that if we want to improve our ability to train, and to develop better training methodologies one start is by modeling the movement that we see, either by somehow digitizing the video, or by motion capture, etc. of willing test subjects.
12-20-2006, 06:54 PM
I can't load a lot of the cooler graphics and vids, but I can offer that the icosahedron is easy and cheap to make. I'm no expert, but we made a six stick icosahedron as a study of tensegrity out of admiration for Bucky Fuller, and to try to design a product for sale. We failed BUT:
If you buy a 1/2" dowel and cut it into six lengths - then hammer finish nails into both ends, you can easily string together the six stick icosahedron. Careful! It takes two people and five hands to manage the damn thing. We used nylon string, which is cheap and doesn't stretch much. I think the knots were two half hitches, which are easy and agreeable to the task.
Start out with rubber bands for ease, but if you make an icosahedron out of nylon string - you can really play with the properties. Ours 'kicked' just like a soccer ball.
I looked up the one link you suggested with the 'two tantiens'. I wonder, would the human tantien correspond to the end of a stick, or to a point where lots of strings cross?
12-20-2006, 09:02 PM
My understanding is that it is where the sticks cross. Hence, "juji." That's what I was looking at.
At least, that is my understanding...there are ppl here with a lot more experience than me, who can probably comment more.
12-21-2006, 05:24 AM
Interesting. My physical therapist has been practicing for twenty years. He is still working out how everything ties together, and how maladies present. BUT, he is an extremely meticulous fellow. His partner looked at me for ten seconds and knew exactly what was wrong; he sees the big picture.
12-21-2006, 03:07 PM
You might also be interested in checking out the book "Anatomy Trains" by Thomas W. Meyers. This book maintains that the fascia layers of the body and the bones form a tensegrity structure. It's an interesting read. I don't have my copy in front of me, but there is a drawing of a small animal (a rabbit if I remember right) which shows the skeleton with tension lines superimposed on it.
I think the idea has merit. If the human body is not a tensegrity structure per se, it as at least stabilized and operated by tension members operating on relatively rigid compression members.
12-21-2006, 05:05 PM
Thanks Michael. I'll look for it. The trouble with models is they, well, are models.
After playing with these a lot in college I concluded that we humans just don't think in three dimensions very well.
12-23-2006, 12:05 AM
Perhaps Erick is busy. How perceptive.
Traditional physiology sees human structure in traditional terms - load bearing members, and sees our joints in terms of 'box joints', and 'ball joints', and 'gliding joints'.
The 'sea change' I am shamelessly begging Erick to have is a paradigm shift. This shift incorporates the 'fascia' that Mike Sigman always mentions. My chief issues with this line of thought is not with what asserts, but with what it denies. What Chesterton called the "clean, well-lit prison of one idea." What makes sense statically, often does not dynamically.
I read Kuhn back in high school in the early eighties. Tensegrity is not that new, nor revolutionary. Its basic principles are used in guyed masts. My father was setting up and taking down guyed radio towers of several hundred feet since the late fifties. The practical use of tensegrity. I climbed them to change light bulbs for money in the summer during high school and college. The name and Snelson's nifty discontinuous compression spaceframes are of the same vintage as Kuhn's book. They have been around since the late sixties. While this application was novel, nothing in the underlying principles is.
I am also trying to get Erick to perceive that the 'immovability' and 'translation to ground' that our talented friends mention is easily explained by tensegrity. ...If one pushes ONE member of a tensegrity structure one is pushing ALL members of a tensegrity structure. I built a hybrid tensegrity treehouse that I designed. Hung from a single tree as a center pivot. Roof was a radial pentagonal spaceframe with a compression bottom chords, concentric inner and outer radial compression rings, all suspended by eyebolts into the trunk with a tension chain top member. The chain runs vertically down through the outer compression ring to hold the outer end of lower radial floor beams and the outer ringframe with the inner beam and ringframe suspended on another set of radial eyebolts. It survived direct hits from Ivan 2004 and Dennis 2005. All because it moved differentially, flexibly and NOT rigidly.
One more thing - the simplest inherently rigid structure is the triangle. If our bones are the 'sticks' in tensegrity and our fascia are the 'strings' - then our body is full of triangles! You'll need to draw that one for me. I don't see it. More critically, rigidity is a static strategy for handling dynamic loads to limit movement in response to imposed load. There lies a philosophical difference of opinion about what is aikido and what isn't, in terms of movement or "not being moved."
I fall in the "movement" camp -- that aikido is fundamentally about movement, internal and external. Applied power is far easier to generate, dissipate and to manipulate dynamically in a moving framework, and even easier in a rotary framework. Movement allows the use of kinetic terms, where the energy is the square of the velocity. In rotation, the angular velocity increase as the inverse square of the radius. Combined in aciton this is amplificaiton or dissption on the order of the fourth power.
Energy can be equally applied or dissipated (positive/negative) by movment combined with rotation. Thus, in purely passive terms, movement and rotation allows one to offset a positive attacking input by dissipating it with the square of the square of the inertial moment of the body's natural rotation, cleverly oriented, all without directly opposing it. You see that principle of geometric dissipation illustrated in the hyper-accelerating falling chain.
That's why I think that the dynamic function of the structure controls far more than its static nature. If it acts like a chain, regardless of the static nature of the fexible joints between rigid subelements, all chains basically function the same way. The nature of the joints just tempers the efficiency of the dynamic.
Square terms in energy equations allow tremendous amounts of concentration or dispersion of energy. Depending how they are applied they can seem grossly disproportionate if viewed in linear additive terms (like trusses and their single sign (tension or compression but no both) structural members. Maybe you can show me a term that flows from the tensegrity structure, as opposed to its dynamics, that generates anything to the fourth power.
With this structure I can stand effortlessly - I can load for koshinage almost effortlessly, and a master can act very powerfully and seem to do it without straining - because no strain is required. No doubt. A truss is very strong for its weight. But NOT mobile. And you have not defined any antomy that answers to the icosahedral structure of joints posited for a tensegrity model.
So then please explain from that perspective why the instinctive (and martially correct) biomechanics for an incipient fight is to lower weight, crouch slightly, placing the legs in curve, rather than a column, complementary to the tegatana arm shape.
12-23-2006, 12:31 AM
Erick, I assert that in the human body - there is no such thing as 'rotation'. There is only 'translation'. Rotation would be non integral to the structure as a whole. Rotation is a body movement which keeps a point fixed. Since Aikido is about "center" and every rotation is fixed about a center, I think I have the better of the argument with regard to Aikido.
Every limb moves as a rotation fixed around a joint, but not always the same joint. The fixed point need not even be within the body being rotated. Every limb has a center of mass about which its own three axis inertial radius and moments are computed.
If a limb begins rotation in one direction from one joint, it can easily be manipulated by causing the "fixed" end to move as it would move if were free to rotate about the center of mass of the limb without changing its interial moment at all. (I really wish Jun allowed diagrams) All that energy is still stored in rotating the same way, but he is now on the moving end, and the energy he was feeding to you -- he is now eating.
I don't understand the chain analogy fully, but it's not just speed that koky develops - it's power. I have addressed power elsewhere. If squared squares or fourth power terms don't do it for you, I can't help.
As to the analogy -- perhaps because it is not analogy, but mere description.
"Dem bones, dem bones, dem dry bones,
Headbone connected to the neck bone,
Neckbone connected to the shoulderbone,
Shoulderbone connected to the armbone,
Armbone connected to the wrist bone,
Wrist bone connected to the handbone,
Now hear the word of the Lord."
Link+connection+ link+ connection+ .... a chain.
12-23-2006, 12:44 AM
I thought these models might help keep things moving.
Good models. Answers some of my questions about plausible joint structure. Needs anatomical correlation, yet. As I have said, however, static description does not equal dynamic description. That skeleton is still a chain in dynamic function --- ESPECIALLY IF --- you relax tension out of it. I think I may have heard something about this somewhere before ...
12-23-2006, 02:01 AM
Heaven's man! Imagine your favorite dog as a child with a chain drooping from his shoulder. Got it? The poor thing would fall over and look at you with baleful eyes - pleading that you would give a more sensible model a chance! Do it for Rover Erick! A chain of solid spheres having no bending resistance and no cohesion will bear compressive load without buckling if it maintains the funicular (hanging cable) curve for that load. This was Coulomb's proof of the function of the catenary shape.
Under self-weight it is an inverted catenary. Externally the funicular load may appear very different for different loads, but internally it is always the same. If the funicular shape is attained, the load path runs in the precise center of the load member. An intriguing observation for Aikido.
If it runs outside the center, relative bending stress develops -- tension on one side of the limb and compression on the other. If it moves outside the limb in the right way then the side of the limb that is in tension to generate load resistance, comes into compression, and the attacker's push cancels itself out. The limb develops an unopposed rotational moment and tends to rotate and buckle. This is how kokyu tanden ho functions mechanically.
See a bigger picture than the bones - look at the tensegrity icosahedron and imagine it strung with rubber bands. If I link several of them - then deform them in a spiral movement - then let go - they spring back. I have just extended my (tensegrity) arm in the rowing exercise. ... Your chain hangs limply from my shoulder. Limp is bad Erick, in more ways than one. Then we do it differently. Flexible motion propagates internal rotations freely, and concentrates (or dissipates) energy with greater efficiency than rigid rotation or translation. I rotate my hips forward which propagates up my spine, through my shoulders and down to my hands throwing them out. No arm muscle involved, They rise without me lifting them without any arm muscle. As a counterexample -- try suriage in a rigid mode. It won't work, or you will overshoot -- you do not generate nearly enough deflection potential in the blade velocity by rigid rotation.
I can accept tensegrity joints hypothetically or not (since you have a few holes to fill), and it does not affect the dynamic structural model I propose. You yourself have illustrated that tensegrity icosahedra are fair approximations of solid spheres. If I understand the premise and the models, then the limbs/ligament assemblies are just stretched icosahedra, and you posit the joints as proper icosahedra. I can even accept, if demonstrated, that tensegrity manipulation may allow for adaptive adjustment of the structure's shaee under load. But it answers none of the other salient points.
Falling chains, whipping and compressive chains are premised on relaxed (i.e. -- not in tension from external load) structure (which tensegrity is NOT), disproportionate manipulation of dynamic energy (which tensegrity does not obviously do), and supercritical responses under load (which tensegrity also does not) (and therefore making reaction or point of load response diffcult to predict and anticipate).
Merely standing quietly is FAR more dynamic, active, chaotic and counterintuitive than your static tensegrity model would suggest.
The leg muscles and ligaments operate in reverse of the direction of the static model "tension spring" model would have to if they directly provided an uprighting force, which I understand your tensegrity model would also do.
And having seen the models, actual anatomy is missing a significant class of structural necessity in the model - the little compressive members (bones?) forming the three coordinate planes of the icosahedra around all of the joints ...
12-23-2006, 09:07 AM
I appreciate the way you answered all relevant points, and were willing to see at least some potential in the tensegrity model. I may not cover all points in my response, but I trust you will bring them back up if they continue to be at issue.
The big 'IF'. Coulomb's spheres are proven mathematically and beyond my skill to dispute, if even understand. But: A chain of solid spheres having no bending resistance and no cohesion will bear compressive load without buckling if it maintains the funicular (hanging cable) curve for that load. This was Coulomb's proof of the function of the catenary shape.
Keeping spheres lined up is pretty darn tricky. It's a big IF.
I would submit that mast rigging and radio towers do not display tensegrity. B. Fuller uses an analogy: Two people dive from opposite ends of a pool, they meet in the middle, turn and push off of one another, and head in opposite directions. No 'ground' is required for tensegrity. He goes on to liken it to 'a balloon':
"The balloon is indeed not only full of holes, but it is in fact utterly discontinuous. It is a net and not a bag. In fact, it is a spherical galaxy of critically neighboring energy events."
"In the geodesic tensegrity sphere, each of the entirely independent, compressional chord struts represents two oppositely directioned and force-paired molecules. The tensegrity compressional chords do not touch one another. They operate independently, trying to escape outwardly from the sphere, but are held in by the spherical-tensional integrity's closed network system of great-circle connectors"
Flexible motion propagates internal rotations freely, and concentrates (or dissipates) energy with greater efficiency than rigid rotation or translation. I rotate my hips forward which propagates up my spine, through my shoulders and down to my hands throwing them out.
The propagation of energy from turning your hip does NOT propagate up your spine. It propagates through your framework as a coordinated whole. Your spine would experience displacement to the side and blow apart if you tried using it like a rigid member.
Source for Bucky quotes:
I liked the reference to 'motion' being necessary to stay standing in a human. My physical therapist said "If you want stability - you'd better be mobile." I had NO idea what the man was talking about. I've disagreed with him before. I like to form my own ideas - to a fault.
Here is a picture of triangles in the human body: http://www.thebodyworker.com/neckmusclesdeep.gif
Going forward, I'll keep reading about statics, and running your ideas past my best friend the engineer and former aikido instructor. He's Real patient about explaining stuff to me.
12-23-2006, 01:36 PM
The big 'IF'. Coulomb's spheres are proven mathematically and beyond my skill to dispute, if even understand. But:
Keeping spheres lined up is pretty darn tricky. It's a big IF. So is kokyu. That's what makes it so powerful, it can both supprt structure and collapse it without warning. If the connection is sound, and the energy of the attack is accepted, the attacker has borne part of his center into the attack, and therefore the combined structure, and his center must also goes with the collapse of that structure. That's how the unliftable body works. The trick is to maintain that structure in this supercritical (top of the hill) mode until the critical moment when he has committed to a place where there is no place to go but the downhill slide.
I would submit that mast rigging and radio towers do not display tensegrity. .... No 'ground' is required for tensegrity. He goes on to liken it to 'a balloon': They don't need ground. I can guy a mast off the ceiling as easily as the ground.
The propagation of energy from turning your hip does NOT propagate up your spine. It propagates through your framework as a coordinated whole. Your spine would experience displacement to the side and blow apart if you tried using it like a rigid member. It is not a sideways turn of the hips. It is the rotation of the hips forward in the sagittal plane and then the stop that causes the top-torso to flex forward also, cascading little internal rotations of the vertebral connections delivering a pulse of that internal rotation down the arms, rotating the limbs at progressively smaller radii and with greater effective moment as a result, and up they come.
The spine can transmit both a relatively rigid rotation of the whole under low impulse, and a wave of small internal rotations up or down the chain of vertebrae for larger impulses. In torsion, for the sideways trunk rotation you speak of, the whole torso acts as stressed skin tube.
There, your balloon image actually works. Breathing in makes the structure stronger in torsion by expanding the inertial radius, and statically pretensioning the intercostal ligaments and abdomen fabric, so that it can absorb compression loads in bending or torsional buckling without opposing muscular tension.
12-23-2006, 03:17 PM
Reference diagram: http://www.ancient-egypt.de/assets/images/image0041.jpg
You can see that the person represented here has a line drawn down the middle. The spine is Behind that line. What supports the weight of the human? The space in the middle of the 'tube'. Note where Fuller speaks of the 'discontinuity' of the tensegrity structure...'the compression members do not touch'. Compression members are the 'sticks' in the icosahedron model.
Ref: this photo: http://www.uni-kassel.de/fb14/stahlbau/tensegrity/tense3.gif
Now, ref this diagram: http://www.bartelby.net/107/Images/small/image409.jpg
Tensegrity structures are like balloons - tension and compression are in balance. They can be represented as spheres, icosahedra, tubes, ad infinitum. They have the advantages of your rigged mast, without needing to be tied down on one side. The structure is independent and whole by itself.
Note this: http://www.fibersource.com/Textile_Arch/Prize_Picturers/Tensegrity%201.jpg
I'm belaboring this point so you can see that the main 'line' of load bearing power in a tensegrity structure may be Empty Space! It is counterintuitive, and I think it is also not how we are ennervated. In balance we feel very little - off balance and we get alarm bells.
Culturally, we like our work ethic! Fie on a kokyu that feels natural! Calisthenics in football and the Navy - were supposed to hurt. Ouch.
You ask And having seen the models, actual anatomy is missing a significant class of structural necessity in the model - the little compressive members (bones?) forming the three coordinate planes of the icosahedra around all of the joints ...
It's a model. The necessity for finding what was doing the work of supporting the human may have come from the observation of the first diagram I mention - the spine is Behind the central line of a human. What holds us up?
12-23-2006, 05:14 PM
To help in looking at this diagram: http://www.bartelby.net/107/Images/small/image409.jpg
I should mention something. Before plywood was invented, wood frame homes had boards nailed Diagonally, at the corners, to keep the box structure from folding up, like parallelograms do without being made of thick materials to take those forces. With plywood, a light frame structure can be used and then 'sheathed' with plywood. I built a lightweight, but large shed in my yard this way - I only had to sheath the outside of the structure.
So, when you look at this: http://www.bartelby.net/107/Images/small/image409.jpg - see the triangles Contained in the plane of the muscle wrapping. The triangle is Inherent in the plane of the plywood. This isn't 'cheating' on using tensegrity to descrbe the human body, because I'm talking about lines of force, not necessarily about finding tension lines and 'little bone' structures that match one to one with the models we use.
The human body is complex, but seems to be based on some simple structures (echoing an early post in the thread). Pulling these out and thinking in three dimensions is tough for us.
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