PhysicalThoughts about Structure:The Elasticityof FasciaAdjo Zorn, Ph.D.Rolf lnstitute@, Boulder, USA and University of Ulm, Dept of Applied Physiology, Germany

Abstract: Collagen is usually regarded as beinginelastic. This results in a very misleadingunderstanding of the role of fascia in the humanstructure.

Aristotle wrote that a heavy object (e.g., abig stone) falls faster than a light one (e.g., aleaf). This would seem so obvious-any childwould agree. (It seems almost as obvious asgeocentrism-the belief that the sun circles theearth once every day.) The obvious was soobvious that it took about 2000 years until therewas a man crazy enough to doubt the obviousand question whether Aristotle had it right. Hedid this by asking Nature herself, in herlanguages of pure mathematics and dirtyexperiment. He is said to have thrown heavy andlight stones from the Leaning Tower of Pisa androlled stones down inclined ramps. He eventuallyfound out that what seemed "obvious" was

wrQng, Without friction,srnall, light stones rolland fall as fast as big, heavy stones. He alsosupported the radical notion of heliocentrism-the fact that the earth circles the sun. Byrelegating questions about nature to theexperimental method, deeming it the highestauthority, Galileo established modem scienceand lost his freedom. Although this examplecould suggest that doubting the obvious canbring trouble, this article will neverthelessquestion a sacred cow in our world of structuralbodywork: the supposed inelasticity of collagen.

When early generations of physiologistsstarted to examine and classifyvarious kinds ofhuman connective tissue they found-amongother stuff-some obviously elastic material,which they called elastin. But mainly they foundan obviously tight material, which they calledcollagen (from the Greek kalla, or glue; whencooked a long time, collagen becomes anamorphous glue). "Collagen is a tough, glue-likeprotein that represents 30% of body protein andshapes the structure of tendons, bones, andconnective tissues."1 This distinction betweenthe "elastic" and "nonelastic" material has been

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deemed-and still may seem to be-obvious. It ismy view that it is as misleading as a glue-relatedexpression for collagen, even though it is stillfound in the majority of books about physiologyand bodywork. For example, even though, Iconsider Structural Bodywork2to be one of themost precise books currently available on thesubject of the elasticity of fascia, we find theusual confusion: collagen "has a tensile strengthgreater than steel; this means that its individualfibers are very inelastic. They...do not stretch" (p.72).

To explain the "artificial" riddle of howelastic fascia can be made from inelastic

collagen, rules of applied mechanics have to becontravened (denying the elastic fiberelongations in Figure 1). As a matter of fact, .quite the opposite is true, with steel as well aswith collagen: both exhibit wonderful elasticity.So it is a pity that even many of the mostscientific papers in well-established physiologyjournals make a distinction between "elastic"fibers and "collagenous" fibers. It is possible thatthis confusion could cause harm, because amisunderstanding of how connective-tissuechanges can lead to the wrong treatment. Forexample, "Certain heredity connective tissuediseases show hyper mobility of the joints anddecreased elasticity of the skin. The lax skin isoften mistakenly said by physicians to showincreased elasticity, a confusion of terms whichhas probably been the basis of certain theoriesabout the nature of the defect in these patients;the elasticity is decreased, not increased." 3

So, what is elasticity and why is elastinusually, and inadequately, regarded as being"more elastic" than collagen? According to themajority of physicists, elasticity is not a quantitybut a quality, so it cannot be either "more" or"less". Under stress, a more or less solid body hasthree ways of reacting (i.e., qualities): it canbreak or it can plastically deform (in either ofthese cases it remains in its new shape), or it canbehave in an elastic way (returning to its originalshape). There can also be a combination of these

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three. Deformations can be very small andalmost invisible. Plasticity, as a result of innerfriction and rupture, swallows the applied energylike a car bumper. In contrast, elasticity is abehavior that stores and r~turns the wholeamount of energy. Elasticity allows deformationbut restores the original shape when theload/ stress is taken away, as seen in a bouncingsoccer ball.

The big difference between collagen and'elastin is stiffness..Stiffness is the value of howlittle an elastic material stretches under a certain

load. It is a quantity that can be counted andcompared and is equal to the slope of the stress-strain curve. Collagen is much stiffer thanelastin. A collagenous tendon usually stretches atmaximum to about 110% of its original lengthbefore it breaks, whereas elastin can elongate

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a spring, at the beginning a little loose human lumbodol'$al fascia (Yahia 1999)

Figure 1. At left, in a perfect spring an increase Tn applied Jorcecauses increased stretch. The curve demonstratesthat double Jorceproduces double.stretch (Rooke's law). The curve's steepness depends on stiffness: the stiffer the material,the lesssteepthecuroe. .

In the middle chart, we see that as pressure is exerted on the initially slack spring, it elongates a lot under a minimumoj Jorce.

At right is a sketch summarizing in principle many curves described byXakia18 (1 !!9.9),with my Gcd,ditionJor elastin,which is not included in Yahia's work. The similarity to the middle curve is clear. The loss due to viscosity makes theelongation oj thefascia lag behind in stretching as well as in returning. The greater the circumscribed area, the greater theloss of energy.

. If you were designing the body's fascia tomove around in the earth's field of gravity,would you want it to fracture with each impact,to constantly yield without a return to its originalshape? Of course not. It is probably okay if alittle friction is produced-especially during acold winter - b~t fascia. should mostly behave inan elastic manner. That is why "God" or"evolution" invented collagen (more precisely,the collagen-glycosaminoglycan-complex), amaterial that is wonderfully elastic under tensilestress. 4,5 .

Fascia is often described as being"viscoelastic", meaning that there is some viscousliquid inside, producing resistance and friction.Viscoelasticity is a form of "plastoelasticity",meaning a mixture of plasticity and elasticity.The energy going into viscous friction producesheat and the force is dissipated-the stretchedfascia will not return on its own to the pointwhere the stretching started. Muscles have to dothe rest of the work. For example, under normalphysiological conditions, an Achilles tendonreturns approximately 93% of the applied stressenergy and loses only 7% to mostly viscosefriction.6

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approximately 230%.7 We could say that underthe same load, collagen loses much less of itsform than elastin does. Or, to put it another way,collagen can take much more loading beforestretching as much as elastin. Or, even moresimply, elastin is softer than collagen. Underconditions of physiological usage, both stretch tovery different elongations but take and returnthe same amount of energy (almost all of it).

The tensile strength of a material shouldnot be mixed up with elasticity or stiffness. It isanother quantity: the maximum amount oftensile stress that a material can be subjected tobefore fracture.

The low value for stiffness makes the elasticbehavior of elastin much more obvious. With

collagen, the high value for stiffness has .important advantages. First, it protects the body'sshape. The way it does this is like climbing ropesmade of woven nylon, which are required by lawto be quite stiff. (Ajumping or running humanstructure should hold its contents as firmly as thepackaging of a sensitive electronic devicedelivered by mail order,) As a falling body youmight think you'd prefer the smooth landingprovided by a nice, soft, long-stretching bungee

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cord, but it is more likely that your body wouldreach the ground and smash before the bungeecord stopped its fall. (For bun gee jumping to befun, a long, free space to fall must beguaranteed.) Secondly, the high level of stiffnessof collagen protects muscles from exhaustion: ifthey had to move bony levers through soft, long-stretching elastin tendons, they would have tomove much further and do much more work.

Thirdly, the stiffnessof collagen makes 'movement faster, which protected us frombecoming prey (moving bones via soft elastintendons would make us very slow).8

Tensile stiffness is called 'Young'smodulus" and measured in gigapascals (GPa).Human tendons have a tensile stiffness a little

less than solid nylon. The Young's modulus of ahuman tendon is 1.5 gigapascals,9while that ofnylon is 3-7 GPa.lOIfwe compare collagen withsteel (ca. 200 GPa) , we should compare elastinwith rubber (0.01-0.1 GPa).

Which is more elastic, steel or rubber? Itmight seem obvious that steel is not elasticbecause there is not much visible elasticity. Butsomebody like crazy Galileo, might experimentby throwing a steel ball and a rubber ball ontothe ground and measuring the height to whichthey rebound. (If you try this yourself, the"ground" must be strong and elastic enough thatit is not destroyed or plastically deformed by thesteel ball. The best surfacewould be a steel .plate.) Usually the steel ban wiIlrebourid to agreater height than the rubber ball. This isbecause elasticity is not about losing shape in animpressive manner but about returning energy.The greater deformation of the rubber ball as ithits the ground produces more internal frictionand more energy is lost.

As far as I know, the friction in pureelastin structures has never been measured. It is

very likely that it is higher than in pure collagenstructures because the longer stretching ofelastin requires more movement of the viscoseliquid, thus producing more friction. Seeing itthis way, elastin is much "less elastic" thancollagen.

Why do fascia and tendons need to beelastic at all? First of all, together with bones theyform shock absorbers to prevent or minimizeinjury. A fall directly onto your skull would giveyou the feeling of what happens without theseshock absorbers. By contrast, landing on yourfeet puts many effective shock-absorbing devices(made out of collagenous fascia, tendons,ligaments, interosseous membranes, and

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retinaculi) between your skull and the ground.The same structures act like springs, making themovement of a running human body resemblean elastic ball bouncing up and down easily. Thisway, muscles don't need to lift the weight of thebody with each step.l! Other than running, it isnot clear yet how elastic fascia facilitates humangait. The Fascia Research Project at theUniversity ofUlm, including the Rolfers, Dr.Robert Schleip and myself, is currently planninga research project on the function of humanlumbodorsaI fascia in walking (demonstrated byan animated video at

www.fasciaresearch.de/swingwalker ). If you dothe right movement work, you might become anexpert in ballistic walking.12 With adequate gaitstyle, the Achilles spring is stretching beforeandrecoiling during each toe-off phase by about 7mm.13 With such a gait pattern, some Mricanwomen are able.to carry the equivalent of 20% oftheir body weight without any muscular effort. 14

What is elastin for? Its low stiffness valueis needed for structures that have to be able to

change shape a lot, like the wall of the aorta(which has to stretch to accommodate thevolume of blood from each heartbeat), thepulmonary alveoli (which have to provide thewhole increased volume required with eachinhalation), and the ligamentum nuchae(especially in quadrupeds that eat grass from theground but at other times walk tall with a head ofheavy antlers).

So why is elastin often found in collagen-dominant tissue? What can a rubber rope doalongside a steel rope? (i.e., Does it ever have theopportunity to work?) This is not clear yet. Tome, the most convincing speculation is thatelastin is kind of "the memory of the tissue" incases of damage. If the collagen fibers are tornapart (while absorbing damaging energy like acar bumper), there is still the elastin, which hasonly elongated, to try to put everything back towhere it belongs. It is important to note,however, that elastin lacks the strong resistanceof collagen. If, for example, somebody has had awhiplash or a sprained ankle, he/she shouldmove or be moved carefully and loading of thetissue avoided until the elastin has pulled thetissue back to where it came from and the

collagen is repaired right at the fresh tears.Enduring load prevents the elastin from pullingeverything back (this can happen easily), thenthe new collagen bridges over long gaps andgrows into a hyper mobile and distortedstructure.

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What is still a big mystery for me is thepurpose of the ligamenta £lava. I cannot believewhat I usually read. How can this soft sheet helpto extend or stabilize the vertebral column whenit is so close to the vertebr.ae's movement axis15,16

and completely surrounded by many massive stiffcollagenous ligaments more distant from themovement axis? What is there that would changemuch in its length or volume? Maybe thepurpose of the ligamenta £lavais rather toprovide a tube for the spinal cord, like the aortadoes for the blood stream? If you, dear reader,can find error in my thinking or offer anyinformation, please be so kind as to contact me.

Now we can reasonably assume thatAristotle knew more about the elasticity of

tendons than the glue makers did. Mter all, hetaught Alexander the Great the natural sciences,and one factor behind Alexander's success washis pioneering large-scale use of torsioncatapultsl7 that used animal sinews (collagen).Mter the crucial siege of Tyre, he even gratefullycanonized one of them. These devices were latercalled ballistafrom the old Greek word ballO-"to

throw." Galileo built his own telescope (one ofthe first) and observed the movement of planetsand moons. It is a pity that he did not invented amicroscope instead - he could have observedthe movement of human limbs, coined theexpression "ballistin"instead of collagen,andsaved us some confusion.

EndnotesI MedlinePlus Encyclopedia, US National Library of Medicine,

www.nlm.nih.gov/medlineplus/ency/article/001223.htm. March 28th,20072 Smith,]. "Structural Bodywork" Elsevier, 2005.3 Wright, V.;johns, RJ. "Physical factors concerned with the stiffness of normal and diseased joints. " Bull.johns

Hopkins Hosp. 106:215-31 (1960).4 Egan, j .M. "Aconstitutive model for the mechanical behavior of soft connective tissues"j .Biomech.

20(7):681-692,1987.5 Sasaki, N. & Odajima, S. "Stress-strain curve and Young's modulus of a collagen molecule as determined by

the X-ray diffraction technique"j. Biomech. 29, 655-658,1996.6 Ker, R.F. "The design of soft collagenous load-bearing tissues"]. Exp. BioI., 202 (Pt 23) :3315-3324, 1999.7 Heine, H. "Grundregulation und Extrazellulare Matrix" Hippokrates, Stuttgart 1997.8 McMahon TA, Cheng GC "The mechanics of running: how does stiffness couple with speed?"]. Biomech. 23

Suppl 1:65-78, 1990.9 Alexander, R.M. "Tendon elasticity and muscle function" Comp Biochem. Physiol A Mol. Integr. Physiol.,

133(4):1001-1011,2002. '

10 http://en.wikipedia.org/wiki/Young.s_modulus

II Zorn; A., Caspari, M. "Why do we hold up the lower arms while running?-Rolfing and Movement, Gravityand Inertia-Toward a Theory ofRolfing Movement" StriIctural Integration. March 2003,www.RolfingB.de/papers/ rmi5. pdf

12 Mochon, S.; McMahon, T.A. "Ballistic walking: An improved model" Math. Bioscience 52:241-260,1981.13 Fukunaga, T.; Kawakami, Y.; Kubo, K; Kanehisa, H. "Muscle and tendon interaction during human

movements" Exerc. Sport Sci. Rev., 30(3):106-110, 2002.

14 Heglund,N.C.; Willems,P.A.; Penta,M.; Cavagna,G.A. "Energy-saving gait mechanics with head-supportedloads". Nature 375 (6526):52-54,1995.

15 Kapandji, LA. "The Physiology of the joints: The Trunk and the Vertebral Column: Volume 3" Elsevier, 1974.

16 Konz, RJ. et al. "A kinematic model to assess spinal motion during walking" Spine 31, E898-E906, 2006.17 Fox, R.L. "Alexander the Great" chapter 13, 2005

18 Yahia, L.H.; Pigeon, P.; DesRosiers, E.A. "Viscoelastic properties of the human lumbodorsal fascia"]. Biomed.Eng. 15(5):425-429, 1993.

Aclmowledgements:Hodeck, K Personal communication 2007. (He is not the least of my sources, although I wished him many timesto hell: he did not allow me one single, nice, quick, non-precise argument and is therefore guilty of this littlearticle'.s iength being threefold what I originally intended.)

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