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Should tissues be subject to the margins of their optimal stress zones?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by markjohconley, Dec 3, 2012.

  1. markjohconley

    markjohconley Well-Known Member

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    Is it physiologically important for their maintenance? / growth? / repair? to be occasionally subject to forces which cause them to be on or beyond the margins of their ZOOS?

    Just reread the Kirby/Spooner/Scherer/Schubert paper IanG mentions.
  2. Mark,
    It is important for tissue to be subjected to loading levels within it's physiological range, or zone of optimal stress (ZOOS) in order to remain healthy. It is important to realise too that both the magnitude of stress and the number of loading cycles are significant in tissue injury. If a tissue is subjected to loading which goes only slightly beyond the ZOOS on a single occasion, this will not necessarily result in clinically detectable injury. However, the same load which is applied to a tissue over several hundred or thousands of cycles, may result in fatigue failure of the tissue and clinical pathology- bend a paper clip out of shape once and you can bend it back again (but you may have narrowed the ZOOS); keep doing it (keep narrowing the ZOOS through micro-failure) and after a number of cycles it will snap (catastrophic failure/ rupture). Different tissues will tolerate more cycles than others and a healthy tissue with a broader ZOOS may survive more loading cycles than a similar unhealthy tissue with an already narrowed ZOOS due to previous injury.

    On the other hand, a single loading cycle of sufficient magnitude may result in catastrophic failure of the tissue. Also known is that "immobilisation" can result in an inhibition of growth, maturation and structural "degradation". If a tissue is loaded within a very narrow range, albeit within it's ZOOS, I think over time the range of the ZOOS would narrow and tissue health may be impaired as a result.

    Of course since tissues are visco-elstic, rate of loading will be important too; as might factors such as creep.

    You ask about repair, as I said in the paper and have intimated here, the ZOOS of a tissue is a dynamic range. Steiner M. Biomechanics of Tendon Healing. J Biomechanics. 1982; 15: 951-958, demonstrated that after 4 weeks healing, rat tendon had about 70% of it's normal stiffness and only 40% of the normal rupture strength. These low values suggest that high loading early on in recovery should be avoided, and that the ZOOS is markedly reduced. Pushing the loading to the boundaries of the ZOOS should probably occur, but note that the ZOOS is markedly narrowed. As the tissue heals, it's ZOOS expands and higher cyclic loading can be tolerated.

    I'm a little pushed for time, and a little low on motivation these days, but I hope this helps.
  3. Bruce Williams

    Bruce Williams Well-Known Member

    you stated, "Also known is that "immobilisation" can result in an inhibition of growth, maturation and structural "degradation". If a tissue is loaded within a very narrow range, albeit within it's ZOOS, I think over time the range of the ZOOS would narrow and tissue health may be impaired as a result."

    I have thought for quite a while now that achilles tendinosis comes from inability of the ankle joint to function through it's normal range of motion leading to degradation of the achilles insertion and / or watershed area.
    It would seem to me that it would fall within your statement of immobilization as above. Do you agree? I will state that there are obviously other components to the pathology, but I have always felt that if you can get the joint to function again with proper orthotic therapy and PT, that you can resolve most of the problem in time.
    my 2 cents.
  4. Ian Linane

    Ian Linane Well-Known Member

    Hi Simon
    Very nicely and succinctly put. Sorry to hear about the motivation levels.
  5. Ian Linane

    Ian Linane Well-Known Member

    Just wondering if anyone has a copy of the paper Mark mentioned?

    "Just reread the Kirby/Spooner/Scherer/Schubert paper IanG mentions."
  6. Agreed.
  7. David Smith

    David Smith Well-Known Member

    Mark the term ZOOS within tissue stress theory is a tautological argument in the way the the description of evolution as the survival of the fittest is a tautological argument. The fittest survive because survivors are the fittest. The Zone or condition of optimal stress is the stress that produces optimal condition. The argument can't be falsified and therefore your question is not valid. It would be like asking 'could a tricycle go faster if it had 4 wheels'?

    Regards Dave
    Last edited: Dec 3, 2012
  8. Mark:

    I liked Simon's reply. Here are some more thoughts.

    Too little stress on the structural components of the foot and lower extremity (i.e. bone, cartilage, ligament, muscle, tendon) will produce a gradual decrease in the ability of those structures to withstand loading forces without failure (i.e. fracture, partial rupture, complete rupture). There are many research papers that have confirmed the fact that a bone or ligament or muscle which is stressed repeatedly below pathologic loads will, over time, develop more resistance to resist those loading forces, or, in other words, become stronger. Therefore, yes, it is physiologically important for all the structural components of the foot and lower extremity to be stressed at non-pathologic levels to maintain their health and function.

    However, too much stress on the structural components of the foot and lower extremity can, as we know, also cause injury to these structures. Whether it is a compression stress, tension stress or shearing stress, the structural components of the foot and lower extremity can all be injured by excessive magnitudes and/or excessive repetition of stress by causing the molecular structure of the tissue to be stressed past its elastic range, which is where tissues should function to prevent injury, and into its plastic range, where permanent deformation of the tissue may occur.

    Here is a graph that diagrams the elastic and plastic range of a tendon. The elastic region is the linear region or Hookean region of the load vs deformation curve (i.e. stress vs strain curve) and the plastic region is the yield region of the load vs deformation curve. At low loads, when the tendon is elastic, elongation will occur with the tension loading force and the tendon will shorten when reduction of the tension loading force occurs, and the tendon will function with little chance of injury. However, at high loads, when the tendon is in its plastic range, the excessive magnitudes of tendon tension force has increased chance to cause rupture or permanent elongation of the tendon or, in other words, to cause the tendon to become injured.
  9. Agreed. As I said in the paper: "Biomechanically, we may consider that each of the body’s tissues has a zone of optimal stress (ZOOS). In order for the tissue to remain in a healthy state, the loading applied to the tissue must be within the range of the ZOOS. From a biomechanical perspective, tissue dysfunction could be said to occur when:

    1. the load is excessive in relation to the mechanical properties of the tissue,
    2. the biomechanical properties of the tissues have decreased in relation to a
    “normal load,” and
    3. both 1 and 2 occur together."

    Ultimately though, its about the transference of energy to the tissue- Just as stiffness was the "new black" a couple of years ago, energy will be the new "stiffness" soon- mark my words, Mark et al. I thought it would be in fashion in 2012, but it didn't really take off. Maybe 2013 will see discussion of tissue energy at the fore...
  10. efuller

    efuller MVP

    I'm going to try and condense what the others have said. By definition of the term Zone of optimal stress, if you go outside that zone, you will cause injury. Repetitive loading will change the absolute values that originally defined the ZOOS. So, ZOOS will vary over time for a given individual. I'm feeling my age.

  11. efuller

    efuller MVP

    Agree with the comment on ZOOS, but disagree with the survival of the fittest analogy. Take the Galapagos finches. There was one island where the ability to crack seeds was key to survival. The birds on that island evolved to have stronger beaks. Now, when you go back to try to explain why birds on one island have stronger beaks than birds on another island you might get a touch of tautology, but I would call it more of a situation of can you really know why something happens over generations. However, the ability to crack seed argument is not circular. If you can't crack the seed, and all there is to eat is seeds, then you are going to be more likely to die than some bird who can crack the seeds.

  12. So, if you can crack seeds because of your shape of bill you survive and breed, hence those with the greatest fitness for and within the environment survive. You could describe it as tautological, but in physics it would probably be described as a law. Similarly, if you have a tissue and apply a given load and it doesn't cause plastic deformation and or microfibre rupture then the loading is within the ZOOS, if it does cause micro-fibre rupture, then the loading is outside of the ZOOS. Tautological? Maybe. Helpful to those trying to understand tissue injury and the role of mechanical intervention within the treatment of biomechanical injury? Probably.

    A request though: please don't turn this thread into a discussion of evolution versus a christian idea of God. Go do it elsewhere, I'm tired enough of Podiatry Arena's boulevard at the moment. I'll be Jimmy Dean, you can fill in the others...

    Attached Files:

  13. David Smith

    David Smith Well-Known Member

    The response was a criticism of how the statement was questioned not the statement itself. Stress is optimal if it does good stuff and sub optimal if it does bad stuff - 'Only good boys do good things' Ah! But what if a bad boy does a good thing? Well then he becomes a good boy - got it!?
    The bird thing is still the survival of the fittest i.e. the finch with the beak fit to crack the seed survives the one who doesn't. The secondary statement, 'big beaks crack tough seeds more easily' is not tautological that is true but survival of the fittest must be true and tautological because if they survive then they must be fit to do so.
    But you could argue that this not survival of the fittest but rather adaptation of the species to the environment. The Bird with the small beak may have migrated to a different place and eat smaller seeds there or they may have adapted to eat seaweed and shrimps and became a shore bird. Nothing died out so nothing could have survived since survive means to cheat death or live on after the death of another. The bad boy didn't die he just became something else but consider this, if the right conditions presented themselves can birds become dinosaurs again.
    Hey lets not go down that road eh!

    A boy is a boy and he can be classified good or bad by what he does, in the same way a force is a force (or force * cross sectional Area = stress) so a stress is a stress and it is classified by what the outcome is. If we assess the outcome as good then this is a good or optimal stress, if we assess the outcome as bad then this is a bad or sub optimal stress.

    So to get back to the original OP - you can't go beyond the ZOOS (I.E. into ZOSOS) to get a good outcome because that is like saying lets make the Boy do some bad stuff in order to become a good person. It's not logical - doesn't work.

    Regards Dave
  14. So, go briefly beyond the ZOOS and cause small scale micro-fibre rupture, sub-clinical tissue injury perhaps (a bit of muscle soreness lets say), then rest and repair, and do the same thing repeatedly over time. Does the tissue ultimately get stronger or weaker? Does the ZOOS increase or decrease with graded over-load? Does the graded, small scale tissue injury (bad boy), ultimately result in a wider ZOOS (good boy)? I presume, on reflection, to think this was the gist of Mark's original question.

    p.s. I think of the ZOOS boundaries being somewhat "fuzzy".
  15. markjohconley

    markjohconley Well-Known Member


    And methinks it's "Reproduction of the fittest", the "survival of the fittest" was upgraded a little while back

    And for loss of enthusiasm, i just called in at my daughters on the way to work to drool at my grandkids...............................
  16. efuller

    efuller MVP

  17. Here is another stress-strain curve (otherwise known as a load-deformation curve) for ligament and tendon. Notice how there is a linear region in the stress-strain curve where the tendon or ligament will lengthen under increasing load, then shorten under decreasing load, returning to its original length. This is the region that tendons and ligaments should physiologically function in to avoid injury. The linear region of the stress-strain curve is also known as the elastic or Hookean region of the curve.

    Now, if the tension loads within the tendon or ligament are increased past the "elastic limit", the tendon or ligament will start to plastically deform since it has now reached the plastic region of its stress-strain curve. What does plastic deformation mean? Plastic deformation means that the tendon or ligament will either have a few fibers rupture, will have many or all of its fibers rupture or that the fibers of the tendon or ligament will slide on one another to create permanent elongation of the tendon or ligament. Therefore, elastic deformation allows the tendon or ligament to return to its original unloaded length after a loading and unloading cycle, whereas plastic deformation will cause the tendon or ligament to lengthen or become less stiff after a loading and unloading cycle.

    The zone of optimal stress (ZOOS) which Simon mentioned in our roundtable discussion (Kirby KA, Spooner SK, Scherer PR, Schuberth JM: Foot orthoses. Foot & Ankle Specialist, 5(5):334-343, 2012) will always be below the elastic limit of the tissue's stress-strain curve, to avoid injury, and will also be above the toe region [the toe region is close to the origin of the stress-strain curve and represents the uncrimping of the collagen fiber crimping pattern] of the curve, where normal elastic tissue loading starts to occur. One must remember that all structural tissues need a certain frequency of loading and unloading cycles in order to prevent tissue atrophy and in order to maintain its proper and physiologic stiffness and strength to allow normal function without injury. However, one must also remember that all structural tissues, when subjected to an increased frequency of loading cycles or to an increased magnitude of loading, may be more susceptible to plastic deformation and injury.

    The important thing for the clinician to do with each patient is to understand the properties of these structural tissues so that an effective treatment plan may be designed that not only unloads the injured tissue sufficiently to allow healing to occur, but will also allow sufficient loading of the tissue, once it has healed, in order to allow maintenance of proper tissue health over time.
  18. Fuzzy and forever changing

    I would also expect that for tissue to strengthen while working in ZOOS or physiological window it would need to be stressed in the upper part of the zone, the closer to the " line " the greater strengthening, but cross the line injury

    which is what you and Dave are saying re crossing the line
  19. drsha

    drsha Banned

    I totally agree with most of what you stated about ZOOS as a concept, theory or logical thought flow

    I have some questions to pose.

    1. How would you measure when the ZOOS is being applied to strenthen rather than inure?

    2. How do you measure ZOOS clinically since it is dynamic as Simon states?

    3. Does this concept of ZOOS relate to another OPTIMAL? There is a dynamic, im-measureable concept related to the biological structure of biomechanics called Optimal Functional Position (OFP) that when approached would expand ZOOS.

    Together, they would revolutionize biomechanics IMHO.
  20. Attached Files:

  21. Even though I don't want to add another layer of complexity to this interesting subject, it must also be remembered that all the body's structural tissues exhibit a mechanical property known as viscoelasticity. Viscoelasticity means that when a tissue is loaded it exhibits both viscous characteristics (i.e. like honey being poured out of a jar) and elastic characteristics (i.e. like a rubber band being stretched and then released).

    Because of their viscoelastic properties, ligament, tendon, muscle, bone and cartilage all will exhibit what is called time-dependent load-deformation characteristics. In other words, when one of the body's structural tissues is loaded by either a compression, tension, shearing or torsional force, it is not just the magnitude of the force that determines the mechanical response of the body's structural tissues to that force, but also the time over which that force is applied to the tissue.

    For example, a 1,000 N tension force that is suddenly applied over a 2 msec interval to the plantar fascia will cause a much different mechanical effect (i.e. greater risk of injury) within the plantar fascia than if that same 1,000 N tension force is gradually applied to the plantar fascia over a 20 second time interval. This time-dependent load-deformation characteristic of the plantar fascia is very much the result of the plantar fascia being viscoelastic.

    The two main viscoelastic properties of the structural components of the body are stress-relaxation and creep (see illustration).

    In creep, if a constant tension force is applied to the ends of a tendon, for example, over time the tendon will gradually elongate or creep while that constant tension force is still being applied to the tendon.

    In stress-relaxation, if a tension force is initially applied to the ends of a tendon, for example, that stretches the tendon to a certain length, over time that tension force will diminish while thr tendon is being held at a constant length. The stress within that tendon will also gradually diminish or will relax.

    Now, when we apply the viscoelastic characteristics of the tissues to our knowledge of the stress-strain curve and the elastic and plastic nature of all the body's tissues, it becomes clear that the zone of optimal stress (ZOOS) should probably not simply be discussed in terms of absolute magnitude of tissue stresses but also in terms of time-dependent tissue loading parameters such as loading rate (i.e. force/time) or strain rate (i.e. strain/time). In other words, perhaps it is more important to also be discussing the zone of optimal stress and loading rate (ZOOSLR) or the zone of optimal stress and strain rate (ZOOSSR), rather than only ZOOS? Perhaps it is not just the magnitude of the load being applied to the tissue that is important in determining tissue health but the rate at which that load is applied that is equally, if not more important?
  22. I presume you mean injure? Pain should be a reasonable indicator.

    You cannot without injuring the patient.

    Position, posture call it what you will, is only one of a number of predictors of tissue stress. It is important to consider position, but in isolation position does not provide enough information to base clinical decisions upon. Optimal functional position would be person and task dependent and dynamic throughout the task from time zero to time= end of task. So at any given time:
    optimal functional position = a function of Genotype + Environment + (Genotype x Environment)

    where: Environment = all non-genetic factors
    I hope that helps.
  23. drsha

    drsha Banned

    Would that be Wolf's and Davis's Laws of bone and soft tissue that govern surgical (and biomechanical) treatment and adaptive biological life structure both micro and macroscopically, in general?

  24. Mark:

    Out of your acorn of query is growing a great oak of knowledge.

  25. Agreed, I mentioned both visco-elaticity and creep in my initial answer to Mark. But didn't expand upon it at that time. I think the key is to think about the area under the stress/ strain curve. This is the energy stored within the tissue. With a higher rate of loading, the tissue is stiffer (slope of the line = stiffness) and the area beneath (energy) the curve is increased, i.e. more energy is stored in the tissue. The tissue can only "hold" so much energy before it fails. So perhaps we should talk about the zone of optimal energy transference (ZOOET). ;):drinks
  26. drsha

    drsha Banned

    That means that you can never prevent an injury because if pain is your indicator, the subject is already injured.
    Shouldn't we be able to apply biomechanics subclinically?

    Does this mean that there are no clinical applications for ZOOS?

    Firstly, wouldn't ZOOS and all biomechanics be genotype and environment dependent as well and apply to your rules?

    Secondly, if instead of a fixed mechanical structure, like lets say a car that follows Newton's Primary Laws implicitly when mechanized we had a biological structure that was person and task dependent and dynamic throughout the task from time zero to time=end of task, would Newton's Primary Laws still apply here for mechanizing the biological structure?

  27. I knew you had mentioned it, and know that you are aware of it, but thought the others following along would benefit from a more complete explanation of viscoelasticity.

    So, now, Dr. Spooner, when is your paper on this subject going to be written so that these great ideas will be published for the education and benefit of future generations of podiatrists?:drinks
  28. I'll recount to you a poem by the late Spike Milligan:

    "Dr O'Dell fell down a well, and broke his collar bone.
    But Dr's should attend the sick, and leave the well alone."

    Sage words.

    To prevent injury you have to be able to accurately predict it; as yet we cannot. So, as a clinician, I'm happy to attend to the needs of the sick and to leave the well alone.

    Did you read the paper I linked? Here it is again: http://ptjournal.apta.org/content/82/4/383.full.pdf

    Not sure what you mean by "my rules"? We could say any quantified biomechanical variable is a function of genotype + environment + (genotype x environment). This is one of the reasons why we should not attempt to group individuals together by foot-type, yet rather treat each individual as an n=1 study in progress. This is the fundamental flaw within reductionist systems of biomechanics.

    Newtons Laws still apply Dennis, that's why they are called "Laws":rolleyes:.
  29. drsha

    drsha Banned

    A very black and white poem that makes your opinionated case.

    So check ups, vaccinations and preop antibiotics are bad medicine? No Comprendo mi amigo?

    Very black and white again. So if you're not sick, you're well.
    There are those whose white blood counts are high, they are not performing optimally and they have just visited a TB ward for two weeks. No preventive care here?
    This goes back to scientist and medical practitioner which includes art. We differ here but lets not dwell.

    not recently

    Foot-Typing is a starting platform for care where patients are profiled into subgroups on an intermediate basis for further n=1 care. This reflects a lack of knowledge about FFting, nothing more.

    I stated Newton's Primary Laws (I, II and III). When i stop rolling down the hill by my own biological force, additional computations and complications enter the sphere.
    We differ on this as well so I will not bring it up again if you won't so that we can debate this interesting thread further.

  30. blinda

    blinda MVP

    My late mother bought me `A Children`s Book of Silly Verse` in the mid `70s, within which contained the above (although my version asserts that it was Dr Bell, not Dr O`Dell....), plus my all time Milligan favourite;

    "Today I saw a little worm wriggling on his belly. Perhaps he`d like to come inside and see what`s on the telly."

    Milligan often joked that he wanted to be buried in a washing machine, "Just to confuse the archaeologists" but he is actually buried with a headstone that reads (in Irish) "I told you I was sick."

    Sorry to detract. Back to the thread.....or not, if it`s now about foot-typing :rolleyes:
  31. Yeah, whatever Dennis. Your red-herring of a fallacy notwithstanding, we were talking biomechanics and biomechanical injury, not systemic disease. When was the last time as a podiatrist you gave an inoculation to someone? Moreover, when was the last time you gave them an inoculation which prevented them from falling down a well? There was more than one reason I quoted that from Milligan. How does musculoskeletal injury occur, not systemic disease, musculoskeletal injury? Perhaps if you had bothered yourself to read the papers I linked to, rather than spouting off as per usual, you might be able to demonstrate greater insight. Your foot-typing system is a dog, as we all know, and predicts little if anything at all with regard to musculo-skeletal injury. You're much too clever for me though Dennis, so I must bow out of further discussion with you. That, and the fact that I find you to be the most obtuse, ill-read and obnoxious person it has ever been my misfortune to encounter; I spurn you, as I would spurn a rabid dog and wish you a really miserable Christmas.
  32. Yet another very good, educational thread that Dennis is trying to hijack to advertise his patented, trademarked "Functional Foot Typing". :bang::craig::deadhorse:

    Moderators, how much more of this **** do we need to tolerate before we all lose interest in trying to use our spare time and energy to attempt to make good, educational threads here on Podiatry Arena and then have people like Dennis turn the thread into an advertisement for one of their products? Something needs to be done since I've about had enough!:mad:
  33. Kevin, it's my fault since I mentioned the word "foot-type". Being ego-centric, Dennis automatically assumed that this was free-reign to talk about his functional foot-typing system. As I said at the start of this thread, I am lacking in motivation at the moment to write on Podiatry Arena. This abhorrent man is one of my primary de-motivators. Time for a break.
  34. drsha

    drsha Banned

    I will bow out for a while as you are making very valuable and valid points and I am but a distraction.
    Please reconnect.

  35. Like I said: whatever, Dennis.
  36. The concept of energy absorption by specific structural components, as Simon stated, may be an important parameter which determines whether they are injured or not by a loading force. First, work (W) is defined as the force (F) acting on an object multiplied by the distance (d) the object moves. Therefore W = F x d.

    The work-energy theorem states that the work done on an object by a net force equals the change in kinetic energy of the object. Therefore, work and kinetic energy are interrelated.

    However, when kinetic energy is applied to a tendon to cause it to elongate, that kinetic energy causes the tendon to store energy as potential energy, which is then released as kinetic energy when the tendon recoils back to its original length.

    My question is this: how might we use the concept of energy absorption and work to determine which tissues will be damaged when they are required to absorb kinetic energy and become deformed?

    By the way, I don't know the answer....just thought Simon, Eric or someone else may be able to answer that question for me.:drinks
  37. I don't know the answer either, and I'm horrible at energetics.

    As some of you know, a couple of years ago I set out to write a series of papers on "how foot orthotics work", to date I have not completed this task, but still hope that one day I will. The problem is: it's more of a book than a series of papers when you start to think about the topic in depth. One of the topics I started to discuss within these papers was that of energetics. As Kevin has suggested, when the foot impacts with it's supporting surface, some of that energy is transferred to the surface and some of the kinetic energy is also transferred to the tissues of the foot and lower limb by virtue of elastic strain (potential energy) storage within the tissues. What we don't want to do is to transfer too much energy to the supporting surface which cannot be recovered by the body; equally we do not want to loose too much energy to the body's tissues in a form that cannot be recovered, i.e., heat, since these would both increase the metabolic cost of locomotion. We certainly don't want to attempt to store too much strain-energy in any one of the body's tissues, since this would result in injury. I believe that one of the ways in which foot orthoses can work is that they can act as an external reservoir for energy. That is, they can absorb a proportion of the kinetic energy from the body- releasing it from the tissues and preventing "energy overload" within them. But then, the orthoses can also transfer some of that energy back to the body to aid in locomotion, lowering metabolic cost of locomotion. It all comes down to the stiffness (load/ deformation) characteristics of the orthoses, as McMahon demonstrated with his tuned tracks.
  38. Simon:

    I believe I am less convinced than you are that the function of orthoses can best be understood by trying to determine the energy transfer between the foot and the orthosis. Given the minimal deformations of an orthosis plate, and the negligible deformation of the orthosis plantar to the calcaneus and metatarsal heads, I simply don't think that a conventional orthosis has enough ability to deform to signficantly "absorb energy", especially when compared to the ability of the individual's hips, knees and ankles to flex upon ground impact, and the ability of a shoe midsole to deform upon impact.

    In other words, unlike McMahon's tuned indoor track at Harvard, which will significantly deform upon impact of the runner's foot with the track, effectively allowing the center of mass to lower toward the ground in a controlled fashion so that the runner's legs don't need to perform that function, a foot orthosis, by itself, adds little to the individual's ability to lower their center of mass toward the ground versus what would occur while in a shoe without an orthosis.

    Rather, the main function of the orthosis is to alter the magnitudes, plantar locations and temporal patterns of the reaction forces acting on the plantar foot, in order to decrease either the external loading forces on specific plantar structures and/or to decrease the loading forces on any injured or painful internal structural components of the foot and lower extremity. In other words, the main function of the foot orthosis is not necessarily to "absorb energy".

    While I agree that "energy absorption" may be one of the many functions of a foot orthosis, I believe "energy absorption" is a minor function of the foot orthosis in most cases and, intrinsically, a foot orthosis has very limited capability to absorb energy itself. In fact, the foot orthosis may absorb much less energy than the shoe midsole that it is sitting on top of. Of course, in a stiff soled shoe, while walking on concrete, the foot orthosis with a 6 mm thick neoprene topcover and flexible, congruent medial and lateral arch may allow some impact energy to be absorbed. However, a relatively stiff polypropylene plate without a topcover being placed into a neutral running shoe with a thick midsole will probably not aid in energy absorption for the individual at all and may, by preventing the foot from sinking into the midsole upon impact, may actually decrease the shock-aborbing ability of the shoe.

    Unfortunately, due to the high variability of shoe design, the corresponding variability in shoe sole cushioning characteristics, and the wide range of ground surface stiffnesses that individuals perform weightbearing activities on, it may be impossible to have just one orthosis design be "tuned" for each individual that has a wide range of shoes and ambulates on a wide variety of surfaces with different stiffnesses. However, these factors are certainly important to consider when treating the wide range of individuals that are seen in a podiatrist's office who need shoe advice and effective treatment modalities in order to allow them to function and perform optimally in their given daily weightbearing activities.

    Good discussion, mate!:drinks

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