This discussion of tensegrity attempts to simplify the dizzying mechanical complexity of our living structures through the extensive use of metaphor.

Tensegrity

In the field of Structural Integration (SI), tensegrity is a commonly used term. We hear about sailboat masts, tents and the like as metaphors to compare with the more familiar compression model. The compression model is based on placing one thing on top of another, building something that will hold its shape in stasis in an environment held in place by a gravitational force. Earthquakes and storms tumble these things down all the time, though, so this model is hardly adequate for something that is built for motion, let alone the living form in a random world. I am a sailor and have pitched many tents over the years, but I found these concepts inadequate. Perhaps this is because neither the tent fastened to the ground, nor the sailboat mast tacked to its deck is in motion. It has always been very difficult to successfully explain the concept of tensegrity to all but engineering clients until an ubiquitous tensegrity structure came to mind one day: the bicycle wheel. This is a wonderful and simple example of tensile strength and balance in a structure otherwise too light to carry the compressive loads implicit in cycling.

The bicycle wheel is basically composed of a hub (or axle), a rim, many spokes and a tire full of compressed air. The central hub is powerfully constructed. The rim and spokes, though, are very flimsy by comparison. To sit on a rim would crash it to the ground as it promptly crumpled. It is, after all, cleverly shaped and made of extremely lightweight materials, but as a stand-alone, useless for weight bearing. If the rim is laced to the hub by thin tethers of flexible spokes and the tension of these spokes is balanced by a method called truing, the hub maintains its central position in space within the circle of the rim. The entire system is further stabilized around its perimeter by a rubber casing filled with compressed air. Put together in just this way, the wheel stays true and holds its shape without any wobble when it is rolled. Moreover, when its axle is fastened to the forks of the bicycle, the combined weight of the bike and rider do not collapse the wheel and smack the hub into the rim against the ground.  It actually stays in place!  Furthermore, this arrangement is so strong that the rider can ride it right up a curb, causing momentary deformation, but leaving the wheels none the worse for wear.

Eventually, a wheel goes out of true or in more extreme circumstances, a spoke breaks leaving the entire system in danger of transforming into a compressive one and buckling swiftly. The spoke must be replaced and the system must be rebalanced before the wheel can roll down the road again safely as it was originally designed. This is a perfect example of a tensegrity structure, designed for adaptation and efficiency while exposed to random force and motion.

Our bodies are fundamentally designed for the same purpose: adaptation and efficiency while exposed to random force and motion. In other words, our bodies are living tensegrity systems. Instead of rims, spokes, hubs and tires filled with air, though, structurally we are principally made of bone and connective tissue, powered by muscle, nutrition and our nervous systems. Finally, there is a way to simplify this concept and to explain it to our clients in a way in which they can grasp it.

Bone

Bone is unique as a connective tissue especially because of its mineralization. This gives bone quite different characteristics as a material than fascia, the most obvious being that it is less pliable. There is tremendous variability between individual bones in a given human being, but there are also variations between individual human beings.  Proportion, age, sex, health, history and lifestyle are only a few variables that begin to shed light on this overwhelming complexity. There have been papers published over the years in an attempt to describe the mechanical properties and failure rates of bone, but they have necessarily been simplistic in their scope. The irregular shape of any given bone, the combination of compact and cancellous bone, the irregular nature of trabeculae and the close associations with other forms of fibrous connective tissues make analysis all but impossible in any real sense.  Understand that these variables exist even if we all were made of simply one bone. The fact that each of our bones is different from any other within our own bodies compounds this enormously.  Studies have been done on compression and tensile strength along a pure vector (usually the long axis and usually a cadaveric femur) as well as a few on bending load limits. Also, there have been a multitude of studies done on the architecture of bone failure due to these “pure” loads.(3,5,15) This has been analyzed molecularly with great interest. Bone healing, too, has been a hot topic.

What is clear, however, when considering bone as a material, is the fact that it is so exceedingly complex in nature. It even remodels itself based on need, as do the rest of our tissues and systems. So far, few studies have been done to assess load in vivo under normal circumstances, as oversimplification is necessary in developing experimental models for investigation. In one such study,(10)roseate strain gauges were used to assess the deformation characteristics of the calcanei in live sheep. Through these results, bone was at least shown to be elastic in motion and this elasticity was further demonstrated to vary with locomotive speed. There is still so little scientifically proven about the true function of bone as a living structural element.

Throughout the literature, our skeleton is regularly compared to static, compressive structures, such as bridges, buildings, etc. It is expected that we were designed to resist gravity rather than make use of it and that great effort is made to outlast the burdensome effects of the assumed loads.  Note that so many published bone studies are about failure rate and the molecular architecture of failure in bone.

The issue is that we are not compressive structures. First of all, we move. Second of all, our joints are lined with cartilage, a substance soft enough to wear far too quickly under constant compressive loading even with surfaces almost impossibly smooth regularly being lubricated by a substance as unique and efficient as synovial fluid. In fact, we are designed to move efficiently under properly balanced tension in order to accept our compressive loading more gracefully like the bicycle wheel. Figuratively, though, when our spokes fail, we are subject to degeneration into hybridized compressive structures. Our joints consequently wear improperly, and eventually we get them replaced. Isn’t it curious that while the prevailing viewpoint is one of bones and joints resisting chronic compressive forces, x-rays are first consulted to evaluate joint space?  How do these two conflicting expectations coexist?

Still, gravity has been a punishing reality at times in all of our lives and it is difficult to let go of thinking differently. After all, our bodies have weight and those diagrams of bridges and buildings have an appeal. It is not until it is clear that our bones are designed to deform with motion – and even bend in accommodation under certain circumstances, that the brilliance and magnificent design of bone as a tensegrity element becomes not only simpler to accept, but the clear reality.  It is a matter of logic after all.(7,8)

Given what we know and what we do not know to date, let us look at bone from a tensegrity based perspective; the perspective of practitioners of SI.  Let us consider bones as relatively stiff tensegrity elements, resisting (and even using) compression, tension, bending, torsion, torque, shear and all combinations of these as a consequence of living under the influence of a gravitational field while in random motion in a random world.

Using our bicycle wheel metaphor for simplicity, consider the bony elements somewhat analogous to the rim and hub. They resist otherwise impossible compressive and tensile force even when not in motion, but are able to resist a multitude, variety and combination of forces from random vectors in motion while maintaining structural integrity. As a consequence of loading, the rim deforms and the hub changes its relative position to the rim slightly as needed although the deformation is not really visible. The inherent stress involved is dissipated by the motion itself, the air-filled tire and the spokes.

Muscle

Now, how about the muscles?  Don’t we all talk at length about the muscles? How do muscles figure into this tensegrity system? It is best to use yet another metaphor. This time, we will go halibut fishing…

Fishing for halibut involves going out in a boat and fishing on the bottom of the sea. A fishing rig is used, which generally includes a rod, a reel and a fishing line of appropriate length and strength, terminating in something considered irresistible to fish. For bottom fishing, the line is weighted with a lead sinker in order to keep the line at the bottom, regardless of currents and boat drift. The fisher lets line out until the sinker rests just on the bottom. Any slack in the line is taken up and then the reel is stopped in place with a click.

Boats float on the surface of the water, though, and the surface is always changing. Even in calm water, there are excursions the boat takes, up and down, relative to the bottom of the sea while it remains in place relative to the surface.  With the reel stopped, this up and down excursion is adapted to by the flexibility built into the fishing rod. In other words, the rod bends and straightens in order to maintain tension in the line while the sinker and bait rest on the bottom.

When a fish is hooked, however, no amount of rod flexibility and adaptability will bring the fish to the surface. More power is needed in the form of the reel, which is the motor in the system. There are bigger and smaller engines, according to absolute power and speed requirements, just as there are different reels for different kinds and sizes of fish. Using the reel on the rod, the fisher brings the halibut up to the boat and so, finishes the job.

In this metaphor, the rod is likened to fascia, as it is able to adapt and keep the system in stasis and balance by bending and straightening as needed. In fascia, there are contractile elements as well as neurological input and measuring systems that enable this to happen.(11) Fascia, like the fishing rod itself, is able to contract and relax, changing tension and shape to some degree and to do so as randomly needed.

The reel, the motor in the system, is representative of muscle. If a reel were to be removed from the rod, stripped of line and placed in the boat, it could do nothing (the fisher would conversely be hard pressed to bring the halibut to the surface without the reel). The reel functions necessarily by association to the rod and line.  It is sophisticated, in that it can modulate its power and speed of application easily through the input of the fisher, but as a stand-alone part, an engine without a machine, not terribly effective here. Clearly, to complete the metaphor, the fishing line is the epimysium, endomysium and perimysium, connecting the muscle to connective tissue.  The halibut and the boat are the ends this system acts upon. We will call the fisher nervous system input and receptivity.

Muscle enables our tensegrity-based structures to move and to do so quickly. It is an incredible machine in itself, made use of through the fascia and modulated and synchronized by the nervous system. Without it, we would be mostly still, whatever movement could take place would be very slow and the whole point of being lucky enough to be built on the tensegrity model would be wasted.

Given this, it is clear that speaking in terms of musculature while working in the human tensegrity system is not only unclear, but also incorrect. By changing the commonly used language of SI, practitioners clarify to themselves and their clientele the intent of an intervention and complex of interventions, enabling change to take place far more efficiently.

Fascia

The vital importance of fascial tissue as a shaper, connecter and keeper of possibility in and of itself needs to be stressed once more. Within the philosophy of SI, fascia is often referred to as the organ of form. What does that mean and how does it work?  What do we mean by form?  How can we use that to open the whole system to change and greater ease?  Well, now things can really begin to get complicated – and they do – but every effort will be made to be methodical in describing at least the major factors in operation here.

The SI view of the structure is a plastic one of continuous accommodation with bones acting as spacers and the skeleton as a rudimentary shape. Muscles create the possibility of movement around bony articulations by acting as highly sophisticated fascial tensioning devices. Dimensional change of muscles, through sequential and coupled contraction of particular motor units, tensions the fascia enwrapping them, precipitating a change in overall length of tissue and often, movement about a joint. How these things connect up to each other and how they act in concert is the way we take shape and move.  It is infinitesimally complex, so certainly too much for this discussion, but certainly, we can begin.

First we will consider that the bones, the stiffest tensegrity elements in our bodies, articulate about joints of different designs. These joints are pivot points about which torque occurs through the use of leverage. In its most basic sense, this means that movement occurs about the joints through use of effort applied by contractile elements attached at different distances from the joints. Where the attachments are is vital as placement is a determinant of leverage. Officially, torque = force x distance. Another way to understand this is to apply it to a seesaw. Consider that two people who are of identical weight can be functionally heavier or lighter by varying how close to the pivot they sit. Sitting closer, they seem lighter. Sitting farther away, they seem heavier. Getting a grasp of this conceptually allows the practitioner to more precisely understand the effect of a particular individual structure in the whole system (as an example, consider the possibilities of finger flexors versus the adductor of the thumb).

Also, a given amount of effort (force) may be applied over a smaller attachment to the bone, thereby exerting greater, more concentrated effect (more pressure) or may be spread out over a longer, wider attachment (greater surface area), yielding less apparent effect (less pressure). Force can be a pushing or a pulling force and still follow the same rules. Traditionally, this concept is expressed thusly: pressure = force/surface area. Try looking at it this way: imagine two objects of the same mass, but shaped very differently. One is shaped like a dowel resting on end and one like a wide flat board. The dowel will seem heavier than the wide, flat object even though their mass is identical. This is because all of the dowel’s mass is experienced through a small contact area.  The wide, flat object’s mass is experienced as spread out over its far broader contact area.

To illustrate this in our structures practically, imagine how efficiently tensile force is dissipated at any tendinous attachment to bone, since the tendon is continuous with the periosteum and even the bony fibers. Thus, part of the tensile force translates into girdle-like support of the bone itself.

If we know even just these things, it gives us the tools to understand quite a bit more about what is really going on. Bones work through attachments, and where and how these are mean everything in terms of what they can do. Our movement (other than visceral motility and the beating of our hearts) is accomplished through the positional changes taking place about our joints. Understanding the basic concept of torque, or motion about a pivot, it is clear that motion over greater distance will require more force, or contractile capacity. We now grasp that this contractile capacity can increase by using bigger muscles (more motor units) and/or concentrating the power of the muscle available by attaching it to its action point by a precision tendon of smaller surface area that is well placed. So, as we already know, smaller, shorter span muscles are deeper in our bodies and closer to the skeleton. They attach nearer to the actual joints. We have classically called these “being” muscles.

As the need for larger range and quicker movement increases, the muscles available for it are larger, higher volume and generally (but not always) more superficially located. We have classically called these “doing muscles”.  Note that as the span of a given motor system (myofascial unit) increases, the sheer weight of what it is moving also increases.  A fine example of this is the IT band, involving both the gluteus maximus and the tensor of fascia lata muscles.  It originates at the iliac crest and acts as distally as a facet on the lateral tibial condyle, or Gerdy’s Tubercle. It can mediate lifting the entire leg, which weighs quite a bit and is far away from the hip joint, making it seem even heavier. This is impressive. It also helps to guide the entire femur directly through a longitudinal investment to the periosteum along much of its length. Given the fanned fibers of the muscle involved and the infinite possibility in directional action along fascia, it is fascinating to explore all that this system can actually do. This is only the beginning.

Fascia is, of course, integral to each myofascial unit, but also exists as septae, or sheets defining compartments (even in the braincase and visceral space) and periosteum surrounding bone (including here fascial membranes such as interosseus membranes). Connective tissue, in myriad forms, takes the necessary shape and load of our systems. The truly remarkable part is that it is even able to self-regulate and incorporate necessary adjustments when we are out of “true”. As put by Dr. Helene Langevin, “…one can envisage the whole body web of connective tissue involved in a dynamic, body-wide pattern of cellular activity fluctuating over seconds to minutes reflecting all externally and internally generated mechanical forces acting upon the body.”(9)

Fascia as the Organ of Form

To review, deepest are the bony segments and integral with them, the deepest ligamentous attachments between bony segments.  In a basic sense, this order is necessary to keep the structure attached to itself so it can act as a continuous, adaptive string. The deepest muscular structures span the smallest distances by necessity; it is common sense that shorter structures cannot attach to bone through deeper structures that are longer.  Longer and longer spans are achieved through progressively superficial myofascial units, thereby allowing for greater range of motion over increasingly larger regions of the body. This is an important mechanical concept, especially because the same situation is operative when applied to fascial structures.

We have classically called the large, more superficial muscles “doing” muscles.  Perhaps we might need to adjust our own classical viewpoint to see fascia as “being” and muscle as “doing”.  As musculature functions as short time frame motion engines (“doing”, structures), the fasciae functions more as a longer term stabilizer of shape (“being” structures) and center of mass, through which shorter term random motion may successfully occur within a tensegrity framework.

So, let us go back to the fascia as the organ of form.  This is particularly apparent in the superficial fascia. The superficial fascia has been especially disparaged as a functional tissue. Structurally, superficial fascia may in fact, be the Big Kahuna.

Superficial fascia is unique and wondrous in that it can create or amend its shape depending on the needs of the organism at a given time. That it incorporates contractile structures (9,11,12,13,14) which can be modulated and called to action chemically and neurologically(4) through numerous mechanoreceptors(2,7,8) strongly suggests its function as one of continuous accommodation.  Superficial fascia is also the longest-spanning continuous organ with attachments involving strategically vital leverage points. It can change globally or specifically as the need arises. Note that when it is removed, the human loses its greatest tag of uniqueness; in effect, its “self” expression. Certainly, the superficial fascia models itself to our postural and motion habits as well as our structural deficits, tightening itself between surface tacking points to both contain and brace our structures. Mirroring the astonishingly adaptive capacity of all the systems of our human selves, it is capable of changing this “form” as needed and allowed, as new possibilities become available. As sure as the research done to date on the contractile elements endemic to fascia sheds light on this organ’s true function and capacity, the research yet to emerge on the complexity of the collaboration between fascia and our nervous systems will be revolutionary.

Consider the places in the human structure where bone reaches up toward the surface: the crests of the pelvis, the spinous processes of the vertebrae, the sacrum, the cranial base (and indeed, the entire cranium, neural and visceral), the mandibular arch, the spine of the scapulae, the acromions, the clavicles, the rib cage, including the sternum and manubrium, the ends of the long bones of the limbs and finally, the feet and hands. Note that many of these are effective leverage points. Then, consider areas of especially thickened fasciae, just deep to the superficial fascia as tacking points:  the fascia overlaying the sternum and manubrium, the fascia of the superior nuchal line, again, the spine of the scapulae and acromions, the thoraco-lumbar fascia extending up the spine and down to the sacral apex affixing itself firmly to the sacrum, the linea alba and the pubis and inguinal ligaments in association with the rectus sheath. These fasciae have at least one basic function: one of providing the entire structure a reference point. They provide a place from which to move. By adding to this view the septae investing from superficial fascial structures to the periostea of the long bones, the mechanical action available becomes full of possibilities.

Structurally, the serious consideration of superficial fascia is vital to the SI practitioner. As an example, consider the fascia of the ribs and lower trunk.  These fasciae involve, to a greater or lesser extent, individual muscle fibers embedded within them, adding greatly to their contractile capacity and specificity.  They originate and insert on the rib cage and crest of the pelvis, completely surrounding the torso. When these fasciae are released, the relative positional change between the rib cage and pelvic girdle can be dramatic as well as resulting in a considerable amount of decompression of the lumbar spine. The source of considerable compression need not always be deep.

Again, as a review, reconsider the myofasciae superficial to deep. The longest lever arms are necessary for general shape considerations, so superficial fascia functions in that role. Just deep to that are fascial structures that have a far more active role in both shape determination and smaller time frame (quicker) motion. I will call these fasciae hybridized. They incorporate not only myofibroblasts capable of contraction, but muscle fibers, too. These muscles can be as different as stray muscle fibers/bundles or quite massive and powerful, but as “hybrids”, are associated with fascial ends so large or long that their function goes beyond that of tendons. Examples of these are the ilio-tibial band, the abdominal layers and interestingly, many of the structures associated with our limbs. In this light, one must reconsider the function of the psoas minor muscle and perhaps see its function as more like the muscles of the limbs and digits (whose proportion of muscle to fascia is more analogous than the iliopsoas itself).

Certainly, the myofascial needs of the digits are unique, but other hybrid myofascial structures are posited in this discussion which carry out both the maintenance of positional balance within the tensegrity network, as well as perform long range motor movement.

The deepest myofascial layers consist of tissues that (in general) involve more postural functions as they descend as well as contain a higher proportion of muscle to fascia.  A unique, exceptionally deeply located myofascial structure is the heart; the ultimate motor. Suspended both between the cervical fascia (via the mediastinum) and the fascia of the central tendon of the diaphram, it is also directly connected to nearly every cell in our bodies.

<center>Bone Bending as a Tensegrity Strategy</center>

In a previous paper(1) the innominate bones and the myofascial structures arising from their surfaces were compared metaphorically to a bicycle wheel.(Within our whole structures, there are infinite ways to look at segments comprising it as tensegrity subsets, right down to the architecture of single cells.) In this case, the metaphor likened the rim to the crest of the pelvis and the spokes to the origins of both iliacus and gluteal fascia. The abdominal attachments to the crest can be seen as the tire filled with air. These connective tissue structures have their origins over large surface areas, both distributing the forces involved in contracting such powerful tools and providing numerous points at which deformation of the bone can happen. As with truing a wheel, small disparities in balance easily create bowing in the rim. Bending is sometimes necessary in order to hold balance in tension. Thus, it is strongly suggested that the ilium, by its very nature and design, bends.

Once we accept that the ilia bend, we must wonder: but over what time period?  Does it take one’s lifetime to change the shape and mold of this bone, and if so, would it take a lifetime to change “back”?  With all of the literature available explaining mechanisms involved in bone remodeling, it seemed as if this was so. Anecdotally, however, ilia have been seen on several occasions to change shape quite dramatically over a period of less than a minute.

This left room to consider something further: that human ilia are especially designed for heavy tensile, bending and shear loads rather than compressive loads. They are designed to deform as part of their regular repertoire and function as an internal structural self-regulating feature. They bend, curl and change position as required by the tensional elements they are associated with.  Resetting these tensional elements in a strategic way can allow for change over what seem impossibly short time periods. It is fascinating and illustrative to imagine the ilia as flexible internal wings, designed for dynamic motion. Perhaps, they change shape in a small way with each step we take. Whether or not this happens remains to be documented. If bone can be elastic in motion,(10) then why not even more elastic as part of a greater tensegrity function? (It is this author’s opinion that the ilia are not designed to have regular excursions of large magnitude. It would seem that they are designed to be able to do so under unusual circumstances.) We might also begin to wonder what other bones bend.  Clearly, the ribs do, and it is simple to see that the scapulae might, but still one must wonder: is bending of bone, in fact, a necessary component of the tensegrity systems in which we live? Taking this unique function and capacity into consideration while working to restore balance in the human structure and being adds a whole dimension to what is achievable and how we might achieve it. As SI practitioners, recognizing the pattern disparity and the capacity of the ilium to re-set may restore function and limit surgical risks for some of our clients.

In closing, this discussion of tensegrity within an SI philosophy was written as an aid for practitioners who may have been bewildered by the complexity of the notion. Hopefully, this will help us all to come to better clarity when conceptualizing it.  If this discourse has been illuminating, then when working with clients consider recalling the bicycle wheel. If we retain our understanding of tensegrity while we work to de-strain the human structural system, then our intent and specificity can take us all to far greater places. After all, we are truing the wheel, not inventing it.

References

1. Cassuto, S., Intra-innominate distortions: making a case, Structural Integration, 2008; 6(3): 37-39; and elsewhere in this publication.

2. Chen, C. and Ingber, D., Tensegrity and mechanoregulation: from skeleton to cytoskeleton, Osteoarthritis and Cartilage, 1999; 7: 81-94

3. Currey, J, Comparative mechanical properties and histology of bone, Amer. Zool., 1984; 24: 5-12

4. First International Fascia Research Congress, Harvard Medical School, 2007

5. Hildebrand, M, 1974, Analysis of Vertebrate Structure, NY, John Wiley and Sons, Inc

6. Huijing, P.,Muscular force transmission necessitates a multilevel approach to the analysis of function of skeletal muscle, Exerc. Sport Sci. Rev., 2003; 31(4): 167–175

7. Ingber, D., The architecture of life, Scientific American, 1998 Jan: 48-57

8. Ingber, D., Tensegrity: the architectural basis of cellular mechanotransduction, Annul. Rev. Physiol., 1997; 59: 575-599

9. Langevin, H, Connective tissue: a body-wide signaling network? Medical Hypotheses, 2006; 66: 1074-1077

10. Lanyon, L. E., Analysis of surface bone strain in the calcaneus of sheep during normal locomotion. J. Biomech, 1973 Jan.; 6(1): 41-49

11. Schleip, R, Active Fascial Contractility, Structural Integration, 2006 June: 23-25

12. Schleip, R, W Klingler and F Lehmann-Horn, Fascia is able to contract in a smooth-muscle-like manner and thereby influence musculoskeletal mechanics, Liepsch D: Proceedings of the 5th World Congress of Biomechanics, Munich, Germany, 2006: 51-54

13. Schleip, R, Fascial plasticity – a new neurobiological explanation: part I, Journal of Bodywork and Movement Therapies, 2003; 7(1): 11-19

14. Schleip, R, Fascial plasticity – a new neurobiological explanation: part II, Journal of Bodywork and Movement Therapies, 2003; 7(2): 104-116

15. White, A and Panjabi, M, 1990, Clinical Biomechanics of the Spine, Philadelphia, J.B. Lippincott Company

16. Williams, Warwick, Dyson, Bannister, 1989, Grey’s Anatomy, UK, Churchill Livingstone.

A Fresh Look At Tensegrity