Force (Newton)

Force (Newton) Force (Newton)

a perfect spring a spring, at the beginning a little loose human lumbodorsai fascia (Yahia 1999)

Figure 1. At left, in a perfect spring an increase in applied force causes increasedstretch. The curve demonstrates that double force produces double stretch (Hooke'slaw). The curve's steepness depends on stiffness: the stiffer the material, the lesssteep the curve.In the middle chart, we see that as pressure is exerted on the initially slack spring, itelongates significantly under a minimum of force.At right is a chart summarizing in principle many curves described by Yahia (1999),with my addition for elastin, which is not included in Yahia's work. The similarity to themiddle chart's curve is clear. The loss due to viscosity makes the elongation of thefascia lag behind in stretching as well as in returning. The greater the circumscribedarea, the greater the loss of energy.

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A ristotle wrote that a heavy object (e.g.,a big stone) falls faster than a light one

(e.g., a leaf). This would seem so obvious-any child would agree. (It seems almost asobvious as geocentrism—the fact that thesun circles the earth once every day.) The"obvious" was so obvious that it took about2000 years until there was a man crazyenough to doubt the obvious and questionwhether Aristotle had it right. He did thisby asking Nature herself, in her languagesof pure mathematics and dirty experiment.He is said to have thrown heavy and lightstones from the leaning tower of Pisa androlled stones down inclined ramps... Heeventually found out that what seemed"obvious" was \wrong. Without friction,small, light stones roll and fall as fast as big,heavy stones. He also supported the radi-cal notion of heliocentrism. By relegatingquestions about nature to the experimentalmethod, deeming it the highest authority,Galileo established modern science and losthis freedom. Although this example couldsuggest that doubting the obvious can bringtrouble, this article will nevertheless ques-tion a sacred cow in our world of structuralbodywork: the supposed inelasticity ofcollagen.

When early generations of physiologistsstarted to examine and classify variousJkinds of human connective tissue theyfound-among other stuff-some obviouslyelastic material, which they called elastin.But mainly they found an obviously tightmaterial, which they called collagen (fromthe Greek kölla, or glue; when cooked along time, collagen becomes an amorphousglue). This distinction between the "elas-tic" and "nonelastic" material has beendeemed-and still may seem to be-obvious.It is my view that it is as misleading as aglue-related expression for collagen, eventhough it is still found in the majority ofbooks about physiology and Rolfing'). Forexample, I consider Structural Bodywork(Smith 2005) to be one of the most precisebooks about bodywork. Unfortunately, on

the subject of the elasticity of fascia, we findthe usual confusion: Collagen "has a ten-sile strength greater than steel; this meansthat its individual fibers are very inelastic.They...do not stretch" (p. 72).

To explain the "artificial" riddle of howelastic fascia can be made from inelasticcollagen, rules of applied mechanics haveto be contravened (denying the elastic fiberelongations in Figure 1). As a matter of fact,quite the opposite is true, with steel as wellas with collagen: both wonderfully exhibitelasticity. So it is a pity that even many of themost scientific papers in well-establishedphysiology journals make a distinctionbetween "elastic" fibers and "collagenous"fibers. It is possible that this confusion couldcause harm, because a wrong understand-ing of connective-tissue changes can leadto the wrong treatment.'

So, what is elasticity and why is elastin usu-ally-and inadequately- regarded as beingmore elastic" than collagen? According

to the majority of physicists, elasticity isnot a quantity but a quality, so it cannot be

either "more" or "less". Under stress, amore or less solid body has three ways ofreacting (i.e., qualities): it can break or it canplastically deform (in either of these cases itremains in its new shape), or it can behavein an elastic way (returning to its originalshape). There can also be a combination ofthese three. Deformations can be very smalland almost invisible. Plasticity, as a result ofinner friction and rupture, swallows the ap-plied energy like a car bumper. in contrast,elasticity is a behavior that stores and re-

turns the whole amount of energy. Elasticityallows deformation but restores the originalshape when the load/ stress is taken away,as seen in a bouncing soccer ball.

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 im-pact? To constantly yield without a returnto its original shape? Of course not. It isprobably okay if a little friction is produced-especially during a cold winter — but fasciashould mostl y behave in an elastic manner.That is why "God" or "evolution" inventedcollagen (more precisely, the collagen-gly-cosaminoglycan-complex), a material thatis wonderfully elastic under tensile stress(Egan 1987, Sasaki 1996).

Fascia is often described as being "vis-coelastic", meaning that there is someviscous liquid inside, producing resistanceand friction. Viscoelasticity is a form of"plastoelasticity", meaning a mixture ofplasticity and elasticity. The energy goinginto viscous friction produces heat and theforce is dissipated-the stretched fascia willnot return on its own to the point where the

Physical Thoughts AboutStructure: The Elasticity of Fascia

Adjo Zorn, Certified Advanced Rolfer

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stretching started. Muscles have to do therest of the work. For example, under nor-mal physiological conditions, an Achillestendon returns approximately 93% of theapplied. stress energy and loses only 7% tomostly viscous friction (Ker 1999).

The big difference between collagen andelastin is stiffness. Stiffness is the value ofhow little an elastic material stretches undera certain load. It is a quantity that can becounted and compared and is equal to theslope of the stress-strain curve (see Figure1). Collagen is much stiffer than elastin.A collagenous tendon usually stretchesat maximum to about 110% of its originallength. before it breaks, whereas elastin canelongate approximately 230% (Ker 1.999,Heine). We could sa y that under the sameload, collagen loses much less of its formthan elastin does. Or, to put it another waycollagen can take much more loading beforestretching as much as elastin. Or, even moresimply, elastin is softer than collagen. Underconditions of physiological usage, bothstretch to very different elongations buttake and return the same amount of energy(almost all of it).

The tensile strength of a material should notbe mixed up with elasticity or stiffness. itis another quantity: the maximum amountof tensile stress that a material can be sub-jected to before fracture.

The low value for stiffness makes the elasticbehavior of elastin much more obvious.With collagen, the high. value for stiffnesshas important advantages. First, it protectsthe body's shape. The way it does this islike climbing ropes made of woven nylon,which are required by law to be quite stiff.(A jumping or running human structureshould hold its contents as firmly as thepackaging of a sensitive electronic devicedelivered by mail order.) As a falling body,you might think you'd prefer the smoothlanding provided by a nice, soft, long-stretching bungee cord, but it is more likelythat your body would reach the ground andsmash before the bungee cord stopped itsfall. (For bungee jumping to be fun, a long,free space to fall must be guaranteed.)Secondly, the high level of stiffness of col-lagen protects muscles from exhaustion: ifthey had to move bony levers through soft,long-stretching elastin tendons, they wouldhave to move much further and do muchmore work. Thirdly, the stiffness of collagenmakes movement faster, which protected usfrom becoming prey [moving bones via softelastin tendons would make us very slow

(McMahon 1990)1.

Tensile stiffness is called "Young's modu-lus" and measured in gigapascal (G.Pa).Human tendons have a tensile stiffness alittle less than solid nylon. The Young'smodulus of a human tendon is 1.5 gigapas-cals (Alexander 2002), while that of nylonis 3-7 G Pa (http: / / en.l•vikipedia.org / wi ki /You ng's_moduIus). I f the compare collagenwith steel (ca. 200 GPa), we should compareelastin 'with rubber (0.01-0.1 CPa).

Which is more elastic, steel or rubber? Itmight seem obvious that steel is not elasticbecause there is not much visible elasticity.But somebody like crazy Galileo mightexperiment by throwing a steel ball and arubber ball onto the ground and measur-ing the height to which they rebound. (Ifyou try this yourself, the "ground" mustbe strong and elastic enough that it is notdestroyed or plastically deformed by thesteel ball. The best surface would be a steelplate.) Usuall y the steel ball will reboundto a greater height than the rubber ball.This is because elasticity is not about losingshape in an impressive manner but aboutreturning energy. The greater deformationof the rubber ball as it hits the groundproduces more internal friction and moreenergy is lost.

As far as I know, the friction in pure elastinstructures has never been measured. It isvery likely that it is higher than in purecollagen structures because the longerstretching of elastin requires more move-ment of the viscous liquid, thus producingmore friction. Seeing it this way, elastin ismuch "less elastic" than collagen.

Why do fascia and tendons need to be elas-tic at all? First of all, together with bonesthey form shock absorbers to prevent orminimize injury. A fall directl y onto yourskull would give you the feeling of whathappens without these shock absorbers. Incontrast, landing on your feet puts many ef-fective shock-absorbing devices (made outof collagenous fascia, tendons, ligaments,interosseous membranes, and retinaculi)between your skull and the ground. Thesam.e structures act like springs, makingthe movement of a running human bodyresemble an elastic ball bouncing up anddown easily. This way, muscles don't needto lift the weight of the body with each step(see Zorn and Caspari in Structural integra-tion, March 2003). Other than running, it isnot clear yet how elastic fascia facilitateshuman gait. The Fascia Research Project at

the University of Ulm, including CertifiedRolfers Dr. Robert Schell) and myself, iscurrently planning a research project on thefunction of human l.umbodorsal fascia inwalking (w\VW.fasciaresearch.de). If you dothe right "functural integration" bodywork,you might become an expert in ballisticwalking (Mochon 1981). With adequate gaitstyle, the Achilles spring is stretching beforeand recoiling during each toe-off phase byabout 7 mm. (Fukunaga 2002). With sucha gait pattern, some African women areable to carry the equivalent of 20% of theirbody weight without any muscular effort(Hoglund 1995).

What is elastin for? Its logy stiffness valueis needed for structures that have to be ableto change shape a lot, like the wall of theaorta (which has to stretch to accommodatethe volume of blood from each heartbeat),the pulmonary alveoli (which have to pro-vide the whole increased volume requiredwith each inhalation), and the ligamentumnuchae (especially in quadrupeds that eatgrass from the ground but at other timeswalk tall with a head of heavy antlers).

So why is elastin often found in collagen-dominant tissue? What can a rubber ropedo alongside a steel rope? (i.e., Does it everhave the opportunity to work?) This is notclear yet. To me, the most convincing specu-lation is that elastin is kind of "the memoryof the tissue" in cases of damage. If the col-lagen fibers are torn apart (while absorbingdamaging energy like a car bumper), thereis still the elastin, which has only elongated,to try to put everything back to where itbelongs. it is important to note, however,that elastin lacks the strong resistance ofcollagen. If, for example, somebody hashad a whiplash or a sprained ankle, he/sheshould move or be moved carefully andloading of the tissue be avoided until theelastin has pulled the tissue back to where itcame from and the collagen is repaired rightat the fresh tears. Enduring load preventsthe elastin from pulling everything back(this can happen easily), then the new colla-gen bridges over long gaps and grows into ahypermobile and distorted structure.

What is still a big mystery for me is thepurpose of the ligamenta flava. I cannotbelieve what I usually read. How can thissoft sheet help to extend or stabilize thevertebral column when it is so close to thevertebrae's movement axis (Kapandji 1974,Konz 2006) and completely surrounded bymany massive stiff collagenous ligamentsmore distant from the movement axis?

16 www.rolf.org SrRu ruRAt. INTEGRATION / MARCH 2007

PERS"CTIVLS

What is there that would change much inits length or volume? Maybe the purposeof the ligamenta flava is rather to providea tube for the spinal cord, like the aortadoes for the blood stream? if you, dearreader, can find error in my thinking oroffer any information, please be so kind asto contact me.

Now we can reasonably assume that Ar-istotle knew more about the elasticity oftendons than the glue makers did. After all,he taught Alexander the Great the naturalsciences, and one factor behind AIexander'ssuccess was his pioneering large-scale useof torsion. catapults (Fox, 2005) that usedanimal sinews (collagen). After the crucialsiege of Tyre, he even gratefully canonizedone of them. These devices were later calledhallista from the old Greek word ballö-"tothrow". Galileo built his own telescope (oneof the first) and observed the movementof planets and moons. It is a pity that hedid not have a microscope-he could haveobserved the movement of human limbs,coined the expression ballistiti instead ofcollagen, and saved us some confusion.

1 According to Wright and Johns (1960),"Certain heredity connective tissue dis-eases show hypermobility of the joints anddecreased elasticity of the skin. The lax skinis often mistakenly said by physicians toshow increased elasticity, a confusion ofterms I-vhich has probably been the basisof certain theories about the nature of thedefect in these patients; the elasticity isdecreased, not increased."

Alexander, R.M. "Tendon elasticity andmuscle function" Coinp Bioehern . PliysiolA Mol. lutegr. Physiol., 133(4):1001-1011,2002.

Egan, J.M. "A constitutive model for themechanical behaviour of soft connectivetissues" J.Bioiiiecli. 20(7):681-692, 1987.

Fox, R.L. "Alexander the Great" chapter13, 2005.

Fukunaga, T.; Kawakami, Y.; Kubo, K.;Kanehisa, H. "Muscle and tendon interac-tion during human movements" Exerc.Sport Sci. Rev., 30(3):106-110, 2002.

Heglund,N.C.; Willems,P.A.; Penta,M.;Cavagn.a,G.A. Energy-saving gait mechan-ics with head-supported loads. Nature 375(6526):52-54, 1995.

Heine, H. "Grundregulation und Extra-zelluläre Matrix" Hippokrates, Stuttgart1997.

Hodeck, K. Personal communication 2007.(He is not the least of my sources, although1 wished him many times to hell: he did notallow me one single, nice, quick, non-pre-cise argument and is therefore guilty of thislittle article's length being threefold what Ioriginally intended.)

Ker, R.F. "The design of soft collagenousload-bearing tissues" J. Exp. Biol., 202 (Pt23):3315-3324, 1999.

Kapandji, J.A. The Physiology of the Joints:The Trunk and the Vertebral Column: Volume3, Elsevier, 1974.

Konz, R.J. et al. "A kinematic model to as-sess spinal motion during walking" Spine31, E898-E906, 2006.

McMahon, T.A., Cheng, G.C. "The mechan-ics of running: how does stiffness couplewith speed?" J. Biomech. 23 Suppl 1:65-78,1990.

Mochon, S.; McMahon, T.A. "Ballistic walk-ing: An improved model" Math. Bioscience52:241-260, 1981.

Sasaki, N. & Odajima, S. "Stress-straincurve and Young's modulus of a collagenmolecule as determined by the X-ray dif-fraction technique" J. Bioniecli. 29, 655-658,1996.

Smith, J. Structural Bodywork. Elsevier,2005.

Wright, V.; Johns, R.J. "Physical factorsconcerned with the stiffness of normal anddiseased joints." Bull. Johns Hopkins Hosp.106:215-31 (1960).

Yahia, L.H.; Pigeon, P.; DesRosiers, E.A."Viscoelastic properties of the human lum-bodorsal fascia" J. Biorned. Eng. 15(5):425-429, 1993.

Zorn, A., Caspari, M. "Why do we hold upthe lower arms while running? Rolfine andMovement, Gravity and Inertia-Toward aTheory of Rolling Movement" Structuralintegration, March 2003.

17S'IRUC rURAL INTEGRATION / MARCH 2007 NA, WW.rolf.org