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"Auto-support" of the foot

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, Nov 30, 2009.

  1. Agreed.

    Good point, Graham. Work with the STJ axis locator seems to show that after heel lift the STJ axis is often closer to the ground distally than it is proximally. In other words the inclination of the axis is the other way around in the sagittal plane. So in this situation the planal dominance is such that we don't get "pure" pronation as defined (see figure 6). The same thing happens at the MTJ, look at Nester's single axis model for the MTJ. You'll see spatial orientation of the axis that should provide tri-planar motions that we don't have words for.:eek::cool:
     
  2. I don't know what an "auto-support configuration" is. My foot can adopt many positions of rotational equilibrium and automatically not collapse under the load.
     
  3. All of the toes, not just the hallux!!!!
     
  4. Graham

    Graham RIP

    Michael,

    b
    Yes, sorry!
     
  5. sorry might take awhile !!!!!

    Wjat do people think about Blinda´s statement about tension of PF during negative windlass
     
  6. Mart

    Mart Well-Known Member


    This seems sound. One thought, does anyone know if the plantar fascia in infants has same morphological cross sectional area/ stiffness profile as the adult foot. I am wondering how much of the variation in plantar fascia profile is inherant and how much adaptive.

    If largely adaptive then that has interesting implication in lots of ways given issues of shoe design for kids, activity levels and developmental environments.

    Anyone have an infant they could lend me for an hour? - I'll do a profile map using US

    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  7. Actually, after initial contact we have a reversing of the windlass in this situation. So following the logic we would be moving from an "auto-supported position" (whatever that is) to a non auto-supported position. Did your foot collapse due to this reversing procedure?
     
  8. efuller

    efuller MVP

    Thanks to Sam Randall for posting the pdf's

    In part 1 the auto support is defined as those three mechanisms and then went to explain them further.

    The calc cuboid locking mechanism occurs when the plantar aponeurosis has tension and "allegedly" compresses the calcaneo cuboid joint. In this same few paragraphs there is a description of the plantar aponeurosis acts as a tension band and when it is cut the foot collapses. The latter is definately true, but not really logically connected to the CC joint compression argument. In many feet, if you take a non weight bearing foot and activate the windlass and you will see adduction of the forefoot on the rearfoot. This adduction will tend to decrease compression of the cc joint.

    The cc joint has a curved medial part and a flat latteral part. With forefoot abdcution the flat parts rotate away from each other (less compression) and with adduction there is more compression of the flat parts of the joints.

    It's hard to see how the calcaneo cuobid locking part of the autosupport mechanism is different than tension in the aponeurosis and compression at the joint surfaces prevent dorsiflexion of the forefoot on the rearfoot.


    The truss or locking wedge effect described in the article seems to be saying that you need compression to hold the bones together, and that this is better accomplished when the metatarsals are more vertical. I think this is the point that he is trying to make in the truss locking wedge section. There is a poor logical connection between the parallelogram of force diagram and the contention in the article that forces can be borne better if the metatarsals are closer to vertical.

    A quote from the article.
    "Considering the above concept of weight flow, or transference to the ground, the ability of the foot to progressively transfer body weight to the ground and then handle ground reactive force that developoes equally and in opposite direction must be related to the position of the foot bones to the ground. Specifically, this relates to the bones of the forefoot that must contend with the total amount of body weight once the heel lifts from the ground. The ability of the metarsophlangeal joint to pivot the base about the head permits the metatarsal shaft to move from a relatively parallel attitude to a more vertical attitude. "

    The part of the above statement that I have difficulty with is that the "ability to handle ground reactive force must be related to ..." This statement, from the article is not entirely accurate. Yes, there are more internal stresses when the metatarsals are more parallel to the ground. However, the structures of the foot are able to withstand these forces. The article implies that they cannot. In fact, the structures of foot must with stand those forces from the time of heel lift till the time of maximal inclination of the metatarsals. Additionally, the time of heel lift is usually in the middle of single support when the entire body weight is on one foot. Maximum angulation of the metatarsals to the ground usually occurs after contralateral foot strike. At that point in time the force will be distributed between two feet instead of just the one.

    The article goes on referring to the three auto support mechanisms (calcaneo cuoboid locking, truss/locking wedge, windlass)

    "Each of the above systems provide a separate piece t0 the overall mechanism, but all are interdependent. When viewed together, these three autosupport methods provide stability and synchronicity to limb motions. Each, however, is dependent on the motion at the metatarsophalangeal joint, particularly the first, for the ability to function properly. If no motion were present at the metarasophalangeal joint, then this site would need to be avoided and no weight could be directed to this site at heel off. Thus, no calcaneocuboid stabilization could occur. If no motion were present at the metatarsophalangeal joint, then the ability to transfer weight and thus use ground reaction for stability would also be lost. And if no motion were present at the metatarsophalangeal joint, then the windlass effect with mechanical resupination would fail to originate."

    Several problems with this paragraph. I described above how the widlass tension does not lock the cuboid. (Let alone the problems with "locking" or "stabilization" definitions.)

    "this site would need to be avoided." It's not avoided. People with functional hallux limitus have calluses at the IPJ. This force is still there but applied distally through a temporarily rigid first MPJ.

    I'm not quite sure how ground reaction for stability is lost.

    Howard and I have been around the stump many times on this. Howard has developed a brilliant system for modifying orthoses with the use pressure analysis. I'm not saying that his system does not work. I am disagreeing with his explanation of how it works. I just wish he would publish his recipe.

    Regards,

    Eric Fuller
     
  9. Brilliant question and line of thought, Martin.

    Grace is currently driving us insane (I just got "told off" at the nursery because her behaviour today did not come up to par- bucking the rules. I've no-idea where she gets it from, probably her mother) so I'd willingly loan her to you for several weeks right now. :drinks
     
  10. Mart

    Mart Well-Known Member


    how about


    autosupport configuration of foot = structural alignment of joints which favours smooth acceleration of body COM, is not dependant on active muscle input but occurs because there is no alternative given a specific direction and velocity.

    Simon you must be a good tennis player given you volleying speed.
     
  11. Rubbish at tennis, table tennis I like. Are we limited to structural alignment of joints? Surely soft tissue tension is important? In fact ,if we get rid of the "not dependant on active muscle input" as during gait there will always be active muscle input, aren't we talking about the preferred movement pathway model?

    This post by Martin raises an important question: if auto-support is a "during movement" thing. Could we take out the contribution of the muscles and have the foot be able to "go through the motions" and still see the foot "supported" or would it collapse? If we built an FEA model and put the foot into the various positions it goes through during gait but took out the supportive role of the active components, in fact everything except the three auto-supportive mechanism listed in the Dananberg paper, would it collapse under loading? I really don't know :cool:
     
  12. Mart

    Mart Well-Known Member

    Implicit in my definition would be effect of ligaments and joint capsules, sorry should have made this clearer.

    I think you hit the crux of the issue precisely here. Is there enough data to create the FEA, I have no knowledge of how to build the model? I feel that despite Dannenberg's lack of rigor and overly zelous claims his basic tenants are sound and until we can disprove them they are best we have on this subject.

    One of the things which I want to explore in the gait case study is evidence for disturbed COM acceleration in what wee might regard as sub optimal autosupport.

    I Need to slow things down a bit, and will take time with that thread.

    Do you normally ship your infants UPS or Fedex?


    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  13. efuller

    efuller MVP

    If you want to take longer strides the STJ should be supinating and the leg externally rotating relative to the foot. One limit to stride length is the end of range of motion of the hip as it rotates over the stance leg. If the leg is internally rotated the hip will not be able to externally rotate relative to the ground as when the leg is externally rotated. We may not always need to take long strides.

    So, when your spouse wacks you as you stare at someone walking you can say I was just thinking about hip rotation. Some have a lot more than others.

    Cheers,
    Eric
     
  14. Sorry Michael, I missed you last couple of posts due to the rate of postings here. First of all what is negative windlass and how does this relate to pronation. I agree that as a joint approaches it's end of range in either direction the soft tissue tension will result in increased stability. If the plantar fascia becomes tighter as we move from a neutral position to a maximally pronated position then it's tension will impact upon the compression forces across the joints of the foot. I was thinking about Daryl Phillips study of midfoot motion when I made the original comment, but I don't think he looked at nonweightbearing and thus would not have had plantar fascial tension. Interesting.
     
  15. Cheers, Eric. So if we want external rotation and supination then a lateral or "low-gear" strategy should be the way forward?
     
  16. I cannot find the thread on I think Craig wrote about it spent the last 20 min to find the post. You might refer to it as reverse windlass.

    The elongation of the foot causes tension on the plantar fascia which causes a plantarfexion moment on the toes. ( there are articles about the importance of this in stopping claw and hammer toes)

    Hopefully Craig can put up a link when he wakes up.
     
  17. Yeah, I understand that, Craig called it "reverse windlass"
     
  18. ok be good to see the whole thing again.

    my point was that even if we have pronation we will still have support provided by the plantar fascia thru a different type of tension. ie not a windlass effect but as the foot elongates the PF will be under strain.
     
  19. Yep, they already exist. All we got to do is convince somebody that has one to carry out the analysis....... But it seems to me that the spatial location of the STJ axis might be key, as this will determine whether the windlass mechanism drives the foot into pronation or supination- this, in turn, will influence the calcaneo-cuboid joint packing.
     
  20. Mart

    Mart Well-Known Member

    I was thinking about this issue too. How does this work for you;

    As the forefoot is loaded, if there is insufficient stiffness from ligamentous resistance to calcaneo-cuboid dorsiflexion there will be delay in hallux loading and 2nd rocker is essentialy lengthenned (ie pre windlass). The implications geometrically are then set up for David Smith's scenario whereby 1st dorsiflexion moments win over Hallux dorsiflexion moments and autosupport fails.

    Here's an illustration of that. I'll find time to look at IPF at metatarsal head and plantar digital area 1st toe see if it is consistent with what I just wrote!


    total conact phase of single step
    Total stance 2nd rocker example.jpg


    same foot and step at instant of heel off and initial detection of force under hallux
    2nd rocker.jpg


    Just as Simon has made the case that sub-talar joint axis position and differential compliance of plantar fascia will effect outcome of windlass in terms of direction of motion imparted, perhaps the same is true regarding the "prepostioning" of the foot accoring to the lateral segement stiffness.

    I dont think this negates the idea of autosupport, it just adds some addtional conditions for it to work optimally. My take on Howards' 1st paper was to justify what he regarded as a valuable theoretical approach to his second paper.

    As you say there are some questionable uses of language regarding mechanics but if we are charitable to meaning plus add some conditions then it seems like a sound theory

    I wonder if Howard would agree/revise his paper given the 20 years or so since he first wrote it? Howard where are you?

    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
    Last edited: Dec 1, 2009
  21. Mart

    Mart Well-Known Member

    Here's the IPFs for the data on the previous post.

    The interpretation might be that elevated midfoot compliance may have resulted in sub optimal 1st ray alignment with subsequent suboptimal conditions for effective windlass and loss of auto support.

    This example will be discussed on the gait case study thread in due course and I intend to solicite alternative interpretion given the evidence. Perhaps any comments on that should be saved for later to keep things tidy, just wanted to show where I am headed with that thread.

    Irrespective of other interpretaion to explain what happened it does meet David Smiths criteria for FncHL so in that sense maintain consistancy for this example at least


    cheers


    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com


    .
     

    Attached Files:

  22. efuller

    efuller MVP

    oops double post
     
  23. efuller

    efuller MVP

    What does failur of auto support look like. I don't know what it would look like from the definitions from Howard's paper.

    What is the difference between autosupport and dorsiflexion stiffness of the various joints of the foot?


    2nd rocker is ankle joint rotation over the stance foot, right? I don't see how that applies here.

    There are not many muscles that directly plantar flex the cuoboid on the calcaneus. So, when there is upward ground reaction force on the heel, downward force from the tibia on the talus and upward force from the ground on the 4th and 5th metatarsal heads, the calcaneocuboid joint will dorsiflex until something stops it. Most of the time that will be ligamentous tension and compression at the joint surfaces. Bending of the lateral foot is independent of hallux loading.


    The instant of heel off is very interesting in this foot. There is very high pressure under the styloid process. This is indicative of low dorsiflexion stiffness of the lateral midfoot joints. (Could be met cuboid or calccuboid joint.) In the picture the windlass is obviously not loaded because there is no pressure on the hallux or 1st met. I can't see how you call this a failure of autosupport (from the windlass). To me, failure implies that it can't handle the load placed on it. In the picture, there is no load on the medial slip of the plantar fascia. Sometimes the lateral slip of the plantar fascia attaches to base of the 5th met and tension in this slip of the fascia and compression of the CC joint will be a contributer to lateral forefoot dorsiflexion stiffness. However, you don't have the slip of the fascia attaching to a phalanx to create a windlass.

    I have to disagree on thinking that it is a sound theory. As I read it, the theory is that unless the hallux dorsiflexes, the foot can't bear weight and this is just not true. Is this the part of the theory you feel is sound? Now a different part of the theory is that lack of 1st toe dorsiflexion can cause problems elsewhere. This I agree with, however I disagree with the explanation of why lack of dorsiflexion is a problem.

    This brings up the issue of the reverse windlass or unwinding of the windlass that has been discussed on this thread. As the foot loads the forefoot will tend to dorsiflex on the rearfoot. The windlass is one of the structures that can prevent dorsiflexion of the forefoot on the rearfoot. In some feet, when they are standing, you can palpate the very tight plantar fascia in the medial arch. In these feet the plantar fascia is contributing to the prevention of dorsiflexion of the forefoot on the rearfoot. Some might call that autosupport. But the support is occuring without dorsiflexion of the toe because the arch has lowered and the windlass has become tight and is helping to prevent further lowering.

    Regards,
    Eric
     
  24. Mart

    Mart Well-Known Member

    Hi Eric

    There is a lot to chew off here so will take a bite and have a chance to regurgitate;

    As you will soon see, this is entirely a flight of fantasy on my part, I have not seen anything written to really substantiate what follows, just trying to articulate my understanding of what I think Howard Dannenberg meant by autosupport using different images.

    If you can discredit as rubbish or even unlikely, fair play, I would value that.

    Since autosupport is an abstract concept, to look at it then certain conditions need to be set up. You can’t have checkmate without having a model or rules for the game of chess.

    OK you said “What does failure of auto support look like. I don't know what it would look like from the definitions from Howard's paper.”

    Picture a pimped up simple passive dynamic bipedal walking model with feet comprising 3 pivots distal to an ankle fixed in dorsiflexion. The pivots are a sprung lateral column, medial column, and metatarso-phalangeal joint tuned for stiffness to co-ordinate the COP from heel to hallux so that body COM moves forward smoothly, allowing transfer of load from side to side . . . . that is what autosupport would look like.

    Failure would be that the passive dynamic walking model wouldn’t move or fall over.

    In the human, failure would mean recruiting active control not moderately to impart stability to cope with normal perturbations such as change in velocity, direction or environment but to manage loss of function either acquired due to disease, injury or inherited inadequacy.

    The consequences if within limits of redundant capacity might be measured and would need to be established. If exceeding redundant capacity result would be MSK overload because of inability of those active units to compensate for loss of this idealisation whilst maintaining the chosen body trajectories for sufficient duration.

    Daydreaming or sci-fi?. . . . . definitely.

    Notwithstanding some obvious flaw(s) which I have missed, Simon did mention a way to try and see if it might be a plausible concept. To use FEA to model what we can already measure, and create a virtual pimped up foot, what a great possibility.

    you said “What is the difference between autosupport and dorsiflexion stiffness of the various joints of the foot? “

    Autosupport of the weight-bearing foot is the coordinated passive automated control of the period from heel off to toe off.

    you said “2nd rocker is ankle joint rotation over the stance foot, right? I don't see how that applies here.”

    2nd rocker as I understand it is what occurs in sagittal plane as the tibia advances over the foot after forefoot contact and before metatarso-phalangeal joint pivoting. Whilst this is typically thought of as the period of ankle dorsiflexion, it likely also involves midfoot dorsiflexion too, it is just that the midfoot motion is relatively invisible unless the plantar ground reaction force is examined. At the end of second rocker autosupport begins.

    For autosupport to be successful the prepositioning at end of 2nd rocker needs to meet certain criteria which involve the setting up the medial column to allow windlass to operate.

    I smell something sparkling . . . . time to go see if my lead turned to gold in the basement experiment.

    Cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
    www.winnipegfootclinic.com
     
  25. Heres the stuff on The reverse windlass mechanism that I was trying to find last night. Thanks for finding it for me Craig.

    So it seems that the PF will always be provivding a degree of support( auto-support) to the foot. The type of support depends on ankle motion( dorsi-plantarflexion) position of STJ axis, position of COP to name a few. much to consider.


     
  26. Mart

    Mart Well-Known Member

    I agree with that. What is more interesting is that 3 steps were measured and this was the only step which displayed this characteristic in such an exaggerated way; will talk more about this on the other thread.


    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  27. Mart

    Mart Well-Known Member

    If you look at the graph there is dorsiflexion force applied across the 1st metatarso-phalangeal joint albeit lower than normal. The issue is the IPF (instant of peak force) timing, which, according to DS's hypothesis is a crucial factor in allowing windlass onset. Considering the IPFs you can see that it is retarded for plantar digital area 1st toe which might describe cause for loss of windlass and alternative foot placement (compensation) subsequently. Perhaps there is better explaination. What do you think might be better alternative explaination?

    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  28. efuller

    efuller MVP

    You could have someone with a peg leg that could have smooth movement of the center of mass. I'm having problems with the usefulness of the definition. I can see smoother gait as a goal of treatment, but how does the concept of auto support get us to that goal. How do you improve autosupport?


    You could leave out the concept of auto support and just focus on tissue overload and the above paragraph would not be changed in meaning. Auto support is an extraneous concept added to the discussion.

    Again definitions: What do you mean by allowing the windlass to operate. In static stance you can palpate a tight plantar fascia. In this foot the windlass is operating to create a dorsiflexion moment on the rearfoot. In most feet, it will be creating a supination moment at the STJ. It will be operating even though the toe is not being dorsiflexed.

    The windlass is not the only structure that creates resupination of the STJ in the late stance phase of gait. I feel that concentrating on the sources of moments that create resupination would be better than trying to work with the concept of auto support.

    Regards,
    Eric
     
  29. Mart

    Mart Well-Known Member

    From an embyolgical point of view evolution has equiped us with a modified fish fin not a peg leg. From an engineering point of view evolution has selected the human foot as the most adventageous end point to date of a tranformation from the fin to allow gait as we understand it.

    Our task in deconstructing what that amounts to is explaining how what we are given might be explained in mechanical terms. So we make assumptions and test them as part of that process.

    My assumption is that evolution likely selected anatomic geometry and a capacity for responsive tissue adaptation to optimise energy conservation. Implicit in that is smooth acelleration of COM since this (but not only this) will conserve energy.

    The concept of autosupport as I see it is an attempt to test the notion that the foot is capable of changing from the "mobile adaptor" to the rigid lever" with mininal muscular input, amd maximal "mechanical intelligence" ie it happens because there is no alternative and without neurological feedback if functioning properly.

    A peg leg is not a mobile adapter. My illustration was an attempt, albeit simplistic, to demonstrate what you asked "autosupport might look like" not how it functions.

    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  30. Mart

    Mart Well-Known Member

    I wrote

    In the human, failure would mean recruiting active control not moderately to impart stability to cope with normal perturbations such as change in velocity, direction or environment but to manage loss of function either acquired due to disease, injury or inherited inadequacy.

    The consequences if within limits of redundant capacity might be measured and would need to be established. If exceeding redundant capacity result would be MSK overload because of inability of those active units to compensate for loss of this idealisation whilst maintaining the chosen body trajectories for sufficient duration.
    I disagree. If you look at the last sentence in my arguement it talks to "compensatory overload resulting form loss of this idealisation", in other words injury attributed to failure of autosupport which was Dannenbergs hypothesis and may be considered a subset of causes of MSK overload (assuming of course autosupport maintains credible status).

    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  31. Mart

    Mart Well-Known Member

    The definition is what we are trying to create. Dannenberg described a set of premises which form foundation for definition which I am sure you understand but are reasonably skeptical about, me too.

    I feel what the "community" has been attempting an re-evaluation. Because an idea lacks rigor doesnt mean it is not true, perhaps what I am attempting is an appreciation of what that rigor might be about.

    Maybe you could comment but in my mind the windlass is only operating "successfully" if the the dorsiflexion moment results in change in inner longitudinal arch excursion.

    Perhaps thats were we have a different interpretation?

    If autosupport is a demonstratable sequence of events which meets certain measurable criteria that is deemed desirable for normal function then it must be worthy of inclusion as a functionaly identifyable characteristic just as ankle joint stiffness might be. The problem is that it may be flawed, and currently also lacks reliable criteria to identify it. I think that is becasue it is difficulty to study and perhaps has been a little overblown given lack of evidence.

    From a personal point of view I look for evidence in my practice because I find the
    the idea compelling and when I apply what I perceive as the principles it seem often to give good results. I accept hat those results may be incidental to to the theory though.

    Concentrating on the moments that create resupination I agree is worthwhile.

    Theoretically that could create a problem if it interfers with another function for which the foot is adapted but not recognised. One of Dannenberg's mantra's, as I understand it, is that using forefoot medial posts to create supinatory moments can create FncHL. This seem plausible if it causes IPP timing to be modified and the IPP ratio (IPP metatarsal head1 / IPP plantar digital area 1st toe) is > 1.

    So I maintain that understanding (or disproving the existance) of autosupport if important.

    cheers


    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  32. efuller

    efuller MVP

    I agree that we need deconstruct the foot that we have to understand how it works. In that task we can take several paths. I'm only saying that the autosupport path to explaining how the foot works is not a good one because it adds levels of abstraction rather than focusing on the engineering of the anatomy.


    How does the concept of autosupport test the notion of rigid lever/mobile adapter? If we are going to look at how the foot adapts to terrain and how it functions as a rigid lever then we just have to look at the anatomy and the forces on that anatomy. If we want to look at efficiency of moving the center of mass we have describe the tasks involved in moving the center of mass and then look at how the foot fits into those tasks.

    Regards,
    Eric
     
  33. Firstly, the mechanism we see in the foot whereby the dorsiflexion of the digits pulls on the plantar fascial insertions is not really a windlass mechanism. A windlass mechanism is usually a mechanical arrangement in which the drum (metatarsal head) rotates. This doesn't happen in the foot. In my view its a misnomer. The "geared effect" is only achieved by dorsiflexing the digits sequentially from lateral to medial, but given the influence of STJ axial position, plus some other factors, this is highly questionable. More on this later, I'm sure.

    Kinetics versus kinematics once again. The "windlass mechanism" doesn't have to change kinematics to be "successful", only the kinetics. In other words, it doesn't have to change the excursion of the "inner longitudinal arch". Moreover, it doesn't just act on the inner longitudinal arch, does it?

    This is a windlass mechanism:
     

    Attached Files:

  34. Thats the classic example that I had as well. But if you read thru the post that Simon lead me thru yesterday it makes sense that the windlass mechanism can occur at any toe and cause differnt things to happen.

    Try the experiement that Simon got me to do. Take off your shoes dosiflex each toe individually and see what happens at the subtalar joint. It may pronate or supinate the navicular may rise or drop and drift or nothing may happen depending on the position of the STJ axis.

    You still have a windlass effect what ever happens.
     
  35. Socrates would be proud. My work here is done.;)
     
  36. Mart

    Mart Well-Known Member

    Hi Eric

    I wrote

    Originally Posted by Mart [​IMG]
    The concept of autosupport as I see it is an attempt to test the notion that the foot is capable of changing from the "mobile adaptor" to the rigid lever" with mininal muscular input, amd maximal "mechanical intelligence" ie it happens because there is no alternative and without neurological feedback if functioning properly.



    Yes of course this needs correction replace "test" with "describe".

    Thanks for your attention by the way, this speeds up my learning, hopefully others too. :drinks


    As far as abstraction vs something more concrete. Would you agree with the premises and arguements which follow. I think they might be important in how we should think.

    Measurement of all the kinetics and kinemetics of the foot gives us the data by which we can then test hypothesis regarding function.

    Abstractions are required to make meaning from these data.

    They are mutually dependant if either is to have any value (from our point of view).

    Since the abstraction of autosupport is complex synthesis of premises, each of which is dependant on a set of rules, it should be relatively easy to disprove a single premise rather than prove all of them.

    There is likely a law of dimminishing return in the timing from collecting data to forming an abstraction. In otherwords if we wait for definitive evidence from measurement the theoretic process will be retarded.

    It is therfore a valid approach to create an abstraction then look at the limited data for evidence of fatal flaw. If your concern about considering abstraction is that it should not be at expence of measurement I would agree. However once the data starts to create intersting patterns our imagination should get to work (plus thats the fun part) which I see is what Dannenberg did.

    I feel we went through that process in the thread on tensegrity, this thread has a similar feel to it. For the most part I have stopped thinking about tensegrity primarily because the ideas whichyou Simon, Dave and Kevin presented persuaded me the idea was flawed.



    cheers

    Martin



    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  37. Has everyone been reading philosophy 101 tonight? :D
     
  38. Changed my mind on this- I was wrong. I was thinking about dorsiflexion of the digits, but really it is the metatarsal head rotating not the digit moving- What do I know- nothing- muppet
     
  39. Mart

    Mart Well-Known Member


    Thanks Simon

    Yes that is a key concept which I had missed. My interpretation was that the bucket needs to move but as you say it is connected to more than a rope.

    need to go think about that

    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  40. Martin, I posted another thought on that as you were writing you response. Forget it, I think I was talking ****. No change there then, some of you will scream with glee. I'll get my coat....

    The kinetics versus kinematics bit stands though.
     
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