Tensegrity - its relevance to the human body
This article arises out a presentation given by Elisabeth Davies at the Sutherland Cranial College "In Reciprocal Tension" course, June 11-13 2004, at Hawkwood College, Stroud, England. It is intended to serve as a résumé of some of the available research on the topic, and is not claimed as original work.
To understand how our bodies support us, traditional thinking has drawn comparisons with classical architecture, seeing the body as composed of columns, beams and cantilevers, where the spine acts like a stack of bricks. But if bodies behave in the same way as this architectural model, we would not be able to bend very far before, like the leaning tower of Pisa, we would become structurally unsound. The kind of reinforcement needed to support just our own weight would be unwieldy, severely limiting our freedom and fluidity of motion. Bending or carrying additional loads would be out of the question.
Thoughts of this nature were in the mind of orthopaedic surgeon Dr Stephen Levin in the mid 1970's. He did an arthroscopy of a knee under local anaesthesia, with the patient standing, with help of a tilt table. He found that, as long as the ligaments are intact, the joint surfaces cannot be approximated. He later repeated this at the shoulder and at the radial head. Nothing in standard Newtonian mechanics could explain how this was possible. His quest for a greater understanding of human biomechanics led him to the Smithsonian Museum. Here, studying and measuring dinosaurs, he calculated that, according to accepted biomechanical thinking, they should never have existed, as they should have crumbled under their own weight. His Eureka moment came one day when he caught sight of Kenneth Snelson's Needle Tower, which stood opposite the museum.
Kenneth Snelson, born 1927 in Pendleton, Oregon, said "my art is concerned with nature in its primary aspect, the patterns of physical forces in three dimensional space." Snelson was fascinated by "the infinite perfection of connections" holding everything together. His curiosity about the structure of matter led him to study the two fundamental weave patterns: two-way fabric weave, forming squares, and three-way basket weave, forming triangles and hexagons. Favouring the three-way weave, which is infinitely more stable, he developed three-dimensional weave cells. These self-contained structural units, which he used as the components of his sculptures, consist of tubes and cables - rigid compression tubes pushing outward, held together by flexible tension cables pulling inward. These polyhedral units could be stacked together making larger "floating compression structures" which still maintained the characteristics of a single unit. The dynamic balance between the inward pull of the cables and the outward push of the tubes, which appear to float within the network, gives them enormous structural integrity, maintaining their shape in apparent defiance of gravity, whether vertical or horizontal. His Needle Tower is made from these components.
Although Snelson came up with the concept of tensegrity, it was Robert Buckminster Fuller who coined the term. The two met in 1948, when Snelson was in art school at Black Mountain College in North Carolina. They shared an interest in the geometry of structure, and when Snelson showed Fuller his early X piece, Fuller immediately saw the potential of this principle of opposing tensional and compressive forces, coining the term "tensegrity" (tension integrity).
Richard Buckminster Fuller (1895 - 1983), "Bucky"
for short, was an inspiring visionary, philanthropist, and passionate idealist.
A multi-talented and multi-faceted radical thinker, and as much a philosopher
as an engineer, he, like Snelson, was interested in what connects everything.
In 1948 Fuller was already developing his ideas on geodesics and the geodesic
dome. Geodesics is based on the mathematics of spatial relationships. Tetrahedra
and octahedra combine to fill space, creating the Isotropic Vector Matrix
("Everywhere the same energy"). The dome is all or part of a sphere, the shell
of which is made of rigid struts forming equilateral triangles. In fact all
geodesic domes are based on the same mathematics as the icosahedron,
which consists of twenty equilateral triangles forming an angulated sphere. The
surface can be broken up into many more triangles, smoothing out the curve into
something more spherical. The "frequency"
of a dome relates to the number of smaller triangles into which it is
subdivided. The struts are under both tension and compression, giving
"tensegrity", which means that the dome is extremely strong despite a relatively
lightweight framework, fulfilling Fuller's ecological dream of
"ephemeralisation" (doing more with less).
Fuller's thinking has had a wide sphere of influence, far beyond the world of architecture. Even a carbon molecule was named after him - the Buckyball, or buckminsterfullerene. The fact that his thinking goes way beyond architecture is underlined in his book written in 1975 in collaboration with E J Applewhite. It is entitled "Synergetics: Explorations in the Geometry of Thinking: The integration of geometry and philosopy in a single conceptual system providing a common language and accounting for both the physical and metaphysical". In it he explores the balance between tension and compression, synergy and energy, gravity and radiation, syntropy and entropy, growth and decay. "There is no up and down in the universe, only in and out". These counter-forces are both aspects of the same thing, existing only in relationship with each other. Compression components create tension and vice versa.
Fuller was developing the dome at the same time that Snelson was creating his tension-vectored sculptures, both different aspects of tensegrity. The geodesic dome is a tensegrity structure with an "exoskeleton" of struts on the outside, which are under both compression and tension. The compression and tension elements can be separated by "jitterbugging" the struts from the outside to the inside, resulting in Snelson's tension-vectored, "floating compression" forms, with an "endoskeleton" of compressive struts which no longer touch each other. In the same way, a rigid icosahedron can be transformed into one which is tension-vectored.
Tension-vectored forms provide discontinuous compression in a matrix of continuous tension. The tension is continuous both in space (i.e. all tensional elements connect) but is also in time, as it is permanently pre-stressed, exhibiting "pre-tension". This is the ingredient which provides great strength relative to the actual weight and substance of the structure. When the structure is under load (including gravity), the stress is shared throughout the tension network, making the whole stronger than its separate parts. Furthermore, the greater the load, the greater the tension and therefore the greater the strength.
Transforming the geodesic form into a tension-vectored form makes the structure much more dynamic. By now it should be clear that this model has more application to the human body than any structure made of columns and beams. Ida Rolf saw its potential, and worked with Fuller in the 60's and 70's. She treated the body "as if" it were a tensegrity structure, and there are a number of articles written by Rolfers at that time.
Dr Stephen Levin took this thinking one step further, maintaining that the body "is" a tensegrity structure, with tension provided by a matrix of connective tissues - ligaments, muscles, blood vessels, nerves and fascia (in sheets, making compartments), giving strength, integrity and pre-stress. Compression is provided by the bones and incompressible fluids in compartments. The bones act like spacers, providing the divergent forces needed to hold the spaces open. He sees the body as "A soft tissue entity, with local bony spacers, rather than a hard tissue entity with soft tissue motor units".
Muscles induce motion and help maintain the pre-stress which we call "tone". When muscles shorten, they also expand width-wise, which puts more tension on the fascial/tensional element, increasing stability. We can deliberately increase tone by contracting muscles, increasing pre-stress before lifting heavy objects. Water in its structured form contributes to tone. Enclosed in fascial compartments, it provides shock-absorption and resists deformation. The fact that joint facets cannot be forced into contact in live subjects is compatible with what we know about the properties of synovial fluid, alternating in state between sol and gel. Viscosity determines the rate at which fluid responds to motion demands and how it performs its role in the tensegrity matrix. Levin also maintains that ligaments act like rubber bands, their elastic rebound contributing to the "spring" in our joints, thus also acting as"movers", e.g. in the foot and knee when walking.
Stephen Levin's website www.biotensegrity.com contains a number of articles explaining the physiological support systems of the body as a whole. He compares both the shoulder girdle and the pelvic girdle to the wheel of a bicycle, where the rim is under compression and the spokes suspend the hub by holding it under tension. This is different from a cart wheel, where the spokes are under compression. In the case of the pelvic girdle, the ring of the pelvis, like the rim of the bicycle wheel, is under compression and the sacro-iliac ligaments act like spokes, suspending the"hub" of the sacrum in a soft-tissue tensional network. The pelvis, as the "rim" of the wheel, has evolved to resist forces from any direction: from above, below, within, distributing the load in any and every direction through its tensegrity network.
In the case of the spine, the model here is not a "tower of blocks" under compression, but of a "tensegrity-truss system that will model the spine right side up, upside-down or in any position, static or dynamic. In a tensegrity-truss model, the loads distribute through the system only in tension or compression. As in all truss systems, there are no levers and no moments at the joints. The model behaves non-linearly and is energy efficient." The ligaments provide a network of continuous tension, with the vertebrae acting like bony spacers. The cranium demonstrates another version of tensegrity, with the compression elements on the surface and the tensional elements (the reciprocal tension membrane) on the inside.
The ability of tensegrity structures to resist omnidirectional forces means that in our bodies balance is modified, and integrity maintained, whichever way up we are, to cope with traction or compression in any dimension. Our tensegrity structure works whether we are standing, lying, or upside down, also in space or deep-sea diving (even if our fluid dynamics find it harder to adapt). Gravity has an interesting part to play here. By giving us weight, it increases the pre-tension in our ligaments and fascia. We have observed how pre-tension strengthens a tensegrity structure. Our ligaments and postural muscles have evolved to hold us in correct balance. Therefore, when the body is in balance, gravity, by increasing the pre-tension, provides support, enabling us to stand upright with minimal muscular effort. This is the basis of the Alexander Technique.
Stephen Levin's interest in biotensegrity extended from the macroscopic to the microscopic level. At around this time, Donald Ingber was researching cell structure at Yale. With the synchronicity which often arises in the development of new ideas, both had a common interest in tensegrity in the body, at both microscopic and macroscopic levels. In January 1998 Ingber published an article "The Architecture of Life" in The Scientific American, proposing a universal set of building principles behind the design of organic structures, from carbon compounds to complex systems. "In living things, form has less to do with chemical composition than with architecture. The molecules and cells that form our tissues are continually removed and replaced; it is the maintenance of pattern and architecture, I reasoned, that we call life".
Here he describes the property of living tissues called self-assembly - a phenomenon in which small components group together to form larger ones. Atoms self-assemble into molecules which self-assemble into polymers, into gels, into organelles, cells and tissues. Self-assembly refers to the way organic structures grow synchronously, all at once, as opposed to the way we would construct a building, starting at the bottom and working up layer by layer. A property of self-assembly is that the more complex forms have new and unpredictable properties which could not be determined by observing the behaviour of their constituent parts. Sodium and chloride combine to make salt, whose properties are very different from either of its components. Living systems are dynamic and non-linear, and this unpredictability is called synergy, as described by Fuller.
Ingber observed "an intriguing and seemingly fundamental aspect of self-assembly: tensegrity". He describes the cytoskeleton as a tensegrity structure. Here, molecules self-assemble into gels or protein polymers, which provide the cell's infrastructure. Ingber describes three different types of protein polymers: microtubules, microfilaments, and intermediate filaments. The microtubules provide the compressive "girders", holding the lattice open and stabilising against lateral compression. The contractile microfilaments provide tension, stiffening and anchoring the nucleus, while the intermediate filaments connect everything, including the nucleus and the cell membrane.
Integrins are molecules that pass through the cell membrane, linking the cytoskeleton to the extracellular matrix. A class of adhesion molecule that binds the cell in place, they give tissue its shape and position, also its relationships. They link the cytoskeleton to the nuclear envelope, nuclear matrix and genes, providing a continuous network through all body tissues from nucleus to skin surface. The nuclear matrix, the cytoskeleton and the extra-cellular matrix together comprise a tissue matrix system which Dr James Oschman calls the "living matrix".
At every level, from microscopic to macroscopic, we are connected by this living matrix, a fundamental part of our tensegrity. On the smallest scale, atoms can be visualised as geometric or polyhedral tensegrity structures, where the opposing forces of the positive and negative charges both hold the atom together and hold open the space within it. Arranging themselves hierarchically, smaller units close-pack inside larger ones. The way in which molecules arrange themselves by "closest-packing" of atoms, and the way one structure will "jitterbug" into another, is a whole study in itself. Thus a bone is a tensegrity structure within itself at every level, atomic, molecular, cellular, tissue. Yet it also behaves as a strut in the larger tensegrity of the body. The body consists of tensegrities within tensegrities.
Tensegrity is inevitably linked with the way our structure evolves during growth and development. At each stage of development, the evolving structure optimises so that it functions with the least amount of energy expenditure, self-assembling into the most expedient, energy-efficient form. The less energy needed to maintain form (resist entropy), the more available for growth, development and propulsion. Tensional and compressional demands determine the alignment of fibres in the self-assembly of both the cell and the extra-cellular matrix. Tensional forces naturally transmit themselves over the shortest distance between two points, hence nature's preference for geodesic forms. (By experimentation, Ingber found that increasing tension within a cell will draw it down into this stress-resistant form.) Geodesic, icosahedral forms crop up everywhere, for example in molecules including structured water, pollen grains, dandelion balls, bee's eyes, and viruses. The double helix consists of icosahedra stacked together.
Another explanation for nature's preference for icosahedra can be found in Fritjof Capra's "The Hidden Connections". He proposes that the earliest cells were formed as bubbles in the scum of the primeval oceans. Pushed together, they became flat-planed icosahedra, creating an internal environment conducive to life. Ingber suggests that biological evolution began in layers of clay, which is itself arranged geodesically. Gerald Pollack, in his book "Cells, Gels and the Engines of Life", theorises that the earliest life forms were gels, created in estuary scum. He outlines the important part that structured water (itself an icosahedron) plays in the body's tensegrity. One of its roles is to hold the negatively-charged surfaces of protein polymers together, thus forming an integral part of the cytoskeleton and contributing to tensegrity on a microscopic scale.
The manner in which a molecule holds its sub-components together, by virtue of its tensegrity, defines the way it will behave. Whatever influences structure will also influence chemical behaviour, triggering a cascade of similar changes in adjacent molecules. This means that"changing cytoskeletal geometry and mechanics could affect biochemical reactions and even alter the genes that are activated, and thus the proteins that are made". This is the meeting point between mechanics and biochemistry. Members of Ingber's group found that by modifying the shape of the cell, they could switch cells between different genetic programmes. Cells that spread flat were more likely to divide, cells prevented from spreading committed suicide and, in between these extremes, cells that were not distorted or restricted behaved in healthy, tissue-specific ways. This process is called mechanotransduction, and it has been shown to mediate not only pathological but also essential biochemical functions in the cell. Thus it would appear that the tissue matrix system controls and co-ordinates cellular respiration. This has vast implications for our osteopathic treatment, and makes us ponder on just how far-reaching the effects are when we bring the body into balance, in an interplay between geometry and chemistry, structure and function.
Our present state of dynamic equilibrium is a result of our tensegrity seeking balance. This dynamic equilibrium is self-maintaining as long as our bodies remain intact and in structural and functional balance. Structure and function are so inextricably bound together in maintaining homeostasis that it becomes academic to separate them. A perpetual dance of compression and stretch, a dynamic interplay of structure and function, continues throughout life, so that it becomes difficult to separate the process of our formation from our current form. This is a self-maintaining cycle, which can go either way: the more balanced and flexible the pre-stressed tensegrity structure, the more readily it absorbs shocks and converts them into information rather than injury, and remains healthy and maintains its shape. But if we lose either postural balance or structural integrity (or both), we lose our tensegrity and the compression becomes continuous, with ensuing wear and tear: disc degeneration, arthritic joints, scoliosis/kyphosis. Enter the osteopath!
However, Ingber argues that tensegrity may be responsible for more than just structural and functional integrity, referring to research at John Hopkins School of Medicine which found that tensegrity is capable of mediating information transfer, utilising the vibrational characteristics of the whole tissue matrix. Different cells and tissues exhibit characteristic resonant frequencies. Tensegrities are natural oscillators, and Inber reported that "transmission of tension through a tensegrity array provides a means to distribute forces to all interconnected elements and, at the same time, to couple, or 'tune', the whole system mechanically as one." Oschman describes a plethora of possible media by which messages can be passed round the living matrix at high speed, independent of the nervous system. Fritz-Albert Popp found that the body emits light particles called photons, which switch on the body's processes. The question is, what is co-ordinating all this activity? This inter-connected web has no part which reigns supreme over the others; its properties depend on the integrated function of the whole.
The answer may lie in quantum physics. Quantum coherence is the ability of subatomic particles to co-operate. Dr Mae Wan-Ho in "The Rainbow and the Worm" says communication is mediated by "the body consciousness inhering in the liquid crystallising continuum of the body.... a special kind of coherence or wholeness which is characteristic of macroscopic quantum systems". Herbert Froehlich of the University of Liverpool introduced the idea that some sort of collective vibration was responsible for getting these processes to co-operate with each other. He maintained that coherence is molecules vibrating in unison, taking on certain qualities of quantum mechanics, including non-locality (the ability of a quantum entity to influence another quantum particle instantaneously over any distance). (Froehlich H: "Long-range coherence and energy storage in biological systems", International Journal of Quantum Chemistry, 1968; 2:641-649. Also Froehlich H: "Evidence for Bose condensation-like excitation of coherent modes in biological systems", Physics Letters, 1975; 51A: 21)
The body's tensegrity, including its quantum dimension, may explain some of our palpatory experiences. Pretension, structured water, the dynamic relationship between the "outward" and "inward" forces of compression and tension on macroscopic and microscopic level, the collective action potential of every cell, must all come within our sensory scope. The communication network of the whole matrix may explain both the immediate and global response to small adjustments in the tensional elements and our ability to sense what is happening in the body as a whole. Whatever our treatment modality, an understanding of the body's tensegrity can only enhance our work. As osteopaths we are in a unique position to explore at first hand the implications of these discoveries at the leading edge of quantum physics.
Elisabeth Davies DO ND MSCC, October 3 2004
tensegrity@edavies.co.uk