Longitudinal Arch Load-Sharing System of the Foot

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For those interested, a paper that I recently wrote titled "Longitudinal Arch Load-Sharing System of the Foot" has just been published online in the Spanish Podiatry Journal, Revista Española de Podología.

Abstract: The longitudinal arch of the human foot is a complex mechanical structure that must be compliant on uneven surfaces and also have sufficient stiffness to allow the foot to be an efficient propulsive organ during walking and running gait. To serve these functions, the longitudinal arch has a unique four-layer load-sharing system consisting of the plantar fascia, plantar intrinsic muscles, plantar arch extrinsic muscles and plantar ligaments. These four layers of tension load-bearing elements, working together with the osseous elements which serve as the framework of the longitudinal arch, work synergistically to increase longitudinal arch stiffness during weightbearing activities. The passive tension load-bearing elements of this loadsharing system, the plantar fascia and plantar ligaments, are not under direct central nervous system control and thus serve to stiffen the longitudinal arch with an automatic stiffening mechanism that is based on Achilles tendon tension and plantar forefoot loading. The active tension load-bearing elements, the plantar intrinsic and plantar extrinsic muscles, are under direct central nervous system control and serve to increase or decrease the stiffness of the medial and lateral longitudinal arches depending on the type and intensity of the prevailing weightbearing activity of the individual. Together, the elements of the longitudinal arch loadsharing system ensure that proper weightbearing function of the longitudinal arch, and the foot and lower extremity, can still occur even when a failure of one of these tension load-bearing elements occurs due to injury

 

I am definitely interested. Nice work Kevin!

 

This is the first time I have seen these principles so clearly stated. In my work I can definitely feel the intrinsic planter muscles respond on Achilles tendon tension. The process of resetting that reflex seems to work best when the client is taught that it is there then taught to use the reflexes thy can control by raising one arch and lowering the other as they shift their weight from one foot to the other. When they have mastered that [they are often amazed that they can do it] The central nervous system is more inclined to reprogram ankle dorsiflexion when the practice stepping forward with the other foot.
So often they are just stuck in a limp that is no longer necessary.

 

This paper is a seminal work by Kevin Kirby who I have long regarded as a bright start in Podiatric medicine. As far back as 1980, I recognized the role of LA compression-tension and a phenomena associated with hard shell footwear such as skates, ski boots and cycling shoes that I termed load-unload oscillation or compression-tension cycling. I'll leave this subject for a future discussion. For now, I will focus on an issue that Kevin touched on his paper; intrinsic passive tension precedes active intrinsic extrinsic processes. The theory I had in about 2010 was that artificially inducing a state of pretension in the intrinsic passive tension processes would potentiate what amounts to second stage active processes.

Here is the introduction from my patent filed on December 12, 2012. Several studies done that found unprecedented results with initial applications of the technology. Perhaps Kevin and others can comment on the principles of the technology in inducing a state of what I term Intrinsic Dynamic Tension.

The patent is available online at:
http://www.google.com/patents/WO201...a=X&ei=FoAnUpXGIcb5iQLnrIGgDQ&ved=0CEkQ6AEwAw

FOOTWEAR FOR USE IN SPECIALIZED ACTIVITIES
This invention relates to footwear for use in specialized activities such as sports
and industrial purposes where a specific performance of the foot of the user is
required.

Structures which artificially induce specific physiologic effects in the human lower
limbs in a non-invasive manner are unknown in the prior art.

The structures of the present invention enable the user to control the maximum
height of the arch of the foot and, in so doing, to control the degree of functional
compression/tension and the associated degree of rigidity in the threedimensional
vault of the arch of the foot. In the absence of extrinsic influences,
Intrinsic physiological processes in the human system define the functional
specification and operational limits of the three-dimensional arch of the foot by
acting to control its maximum and minimum heights. In enabling the user to
control the maximum height of the arch of the foot it is intended that intrinsic
physiological processes act to control the minimal height of the arch of the foot.
The primary contributor to functional tension in the arch of the foot when in a state
of functional compression is the plantar aponeurosis. Although there are
references in the literature that relate the arch of the human foot to the structure
of an architectural truss, no references are known which describe the process by
which physiologic processes render the foot into varying degrees of rigidity by
altering the laxity between the joints of the hard tissue that comprise the arch of
the foot. In view of this, it would not be obvious to anyone that such states can be
induced artificially through the use of non-invasive structures, or that there would
be any use for such structures.

The ability to control the maximum height of the arch of the foot and, in so doing,
artificially control the degree of functional compression/tension in the arch is the
underpinning of the ability to artificially induce physiologic processes that render
the function of the human lower limbs specific to activities such as skating,
cycling, skiing and many other sports and industrial uses. Enabling the user to
control the maximum height of the arch of the foot by association enables the user
to alter the functional specification and operational limits of not only the foot but
the lower limb.

The following definitions are used herein: Plantar Surfaces

Mono-planar surfaces are used as a standardized starting point for the plantar
and heel stop elements. As will become evident, adding additional surfaces to the
plantar surface of the plantar element in conjunction with controlling the maximum
height of the arch of the foot can influence or 'control' the function of the foot and,
by association, the function of the lower limb. Adding additional surfaces and
pivoting means to the heel stop element is done as required to adapt its function
to the intended application.

Arch Height
In order to ensure consistency with regard to references to arch height, for the
purpose of the invention 'height of the arch' or 'arch height' means the height of
the arch of the foot of a user as defined by; the shortest distance between a plane
defined by joining the points of the plantar aspect of the foot under the heads of
the first and fifth metatarsals and the calcaneus to the dorsal surface of the foot
above the proximate location of the medial cuneiform. This definition should be
used in stating the effects of structures of the invention that act to control the
maximum height of the arch of the foot. The specialized activities referred to
herein can be any activity undertaken by the lower limb of the user for applying
force from the lower limb to an element to be activated such as in cycling, skating,
skiing, and many other sports and industrial uses where the forces from the lower
limb are intended to be directed and controlled.

 

Linchpin,

Are you familiar with the beam theory and the concepts of compression member and tension member?

Beam theory paraphrased: When an object is supported on its ends and bears a load somewhere between those ends there will be compression and tension in that structure. This is because the applied load creates a bending moment within the object. For a beam or a tied arch to keep from bending /collapsing under load there must be compression and tension.

I'm curios as to how you "enable the user to control the maximum height of the arch of the foot"
Eric

 

I am intimately familiar with the beam theory and especially what happens if the midspan of a bow truss is 'supported' or obstructed from compressing. This can an often does cause truss to failure because it prevents the load points from carrying the load. One thing that I have not seen mentioned in discussions of arch biomechanics is that the tension aspect in a truss is opposing shear forces. So when the LA compresses and lengthens, it lengthens anterolaterally. The accompanying shear forces serve as reaction force for the Achilles tension.

Kirby was speaking in broad principles. But there were a lot of important aspects that were not in his paper. For example, the Achilles load transfer mechanism is a 2 step phased lever mechanism that starts with soleus isometric arresting shank dorsiflexion at which point the lever arm shfts gears and engages the gastrocnemius-hamstrings in what I term, the pelvic plantar pull.

Paper #25 cited in the References section of Kirby's paper describes a crude mechanism for inducing compression in the LA arch. I created and later patented a far superior method in 1980, 35 years before Kelly et al. There is some very good research being done in Australia. Check out, The Foot’s Arch and the Energetics of Human Locomotion by Sarah Stearne et al. Stearne's group gave a stern lesson in how arch supporting insoles severely attenuate maximum arch compression.

 

I'm curios as to how you "enable the user to control the maximum height of the arch of the foot"
Eric.

I found an issued version of the patent online with the figures. But for some reason, only portions of the figures display.

Enabling the user to control the maximum height of the arch of the foot is quite simple. I'll see if I can import a few of the figures. In the interim, here is a portion of the description that starts after the description of the figures. The only prior art cited against my patent was 3 patents for footbeds and orthotics that limit the minimum height of the arch; the exact opposite of my invention.

DETAILED DESCRIPTION
The invention herein may consist of two principle elements each with separate but complimentary functions and two
secondary elements which are integrated with either or both of the principle elements. With reference to the two primary
elements, the first element is an exoskeleton that serves as both a maximum arch height controller and a three-dimensional,
tri-reaction point, force transfer system.

Heel and dorsal elements act as both force transfer interfaces and locators of the heel and dorsal spine of the foot. Each
element has an outer aspect and an inner aspect which either integrate as a unit or are combined as separate elements with
either the exoskeleton or footwear/liner systems.

The primary form of the invention is an exoskeleton for enabling the user to control the maximum height of the arch with a
heel stop element HS at the rear end. The exoskeleton aligns key structures of the foot in relation to sports equipment such
as skis, ice blades and bicycle pedal spindles and facilitates the exchange of three-dimensional forces. The starting point for
the base or plantar element P is a uniform thickness, mono-planar surface with zero inclination. Structures are added to the
plantar element as necessary in order to induce specific physiologic effects related to the target activity.

 

Here's Figure 3-4 from the patent. This shows how the anterior advance of COM creates a lengthening moment arm as it advances past the vertically stacked position over the distal tibia.

 

Can you explain what you mean by controlling the maximum height of the arch. Are you saying that your device attempts to lower the arch of the foot from where it would be in relaxed stance?

From the picture of the device I'm not sure what forces you are trying to apply to the foot. The anterior part looks like it is trying to apply a downward force and the posterior heel part would apply a posterior to anterior force to the heel.

The downward force on the top of the foot is something podiatrists are going to really have a hard time with. We spend a lot of effort to decrease arch flattening forces. As Kevin showed in his article, and as Kevin and I wrote in our chapter, Achilles tendon tension is quite good at flattening the arch and creating tension in the plantar structures and compression in the bones.

If you put this in a ski boot, I can see how it would make the boot feel a lot tighter. I had some ski boots from the early 90's that had a knob on top that you could twist to make the boot tighter. Was that your device? If not how does your device work differently?


Eric

 

I think what you and pretty everyone else appears to have missed is that THE problem in activities like skiing, skating and cycling is arch decompression - recompression caused by asperities in GRF and unweighting actions. Placing support of any kind under the arch can actually exacerbate this effect.

The other issue that many of your colleagues appear to have bought into is the idea that the human foot works better in activities such as skiing when its joints are immobilized with some sort of form fitted liner and orthotics or insoles that attempt to stabilize the STJ in neutral. What this does is virtually ensure the presence of a large unbalanced inversion-lateral rotation moment of force capable of applying a high transient varus thrust-lateral vertical axial rotation to the tibia against a well stabilized femur. Do you actually buy into this sort of nonsense Eric that rendering the ankle foot complex dysfunctional somehow makes it more functional? If you do, it would appear that on one hand you are lauding the LA load sharing system of the foot and on the other hand taking the position that compression-tension of the LA is a bad thing and should be impeded or prevented. Which is it Eric?

My technology bears no resemblence whatsoever to the devices you refer to which obstructed the synovial fold and prevented Achilles forefoot load transfer otherwise it would not have met the stringent requirement of unobviousness for a patent. My patent went well beyond unobviousness qualifying for original thinking status.

The first in boot technology that I invented in 1980 that attenuated arch decompression enabled Canadian downhiller, Steve Podborski, to compete and win on the most difficult downhill courses in the world mere months after reconstructive ACL surgery, something that is still impossible today, where he was unable to ski at all in a conventional ski boot and after told by his doctors he would not be able to ski for at least 9 months and was out for the season. He easily won the World Cup downhill title, something no other non-European has ever repeated. The technology worked by reducing the strain on his knees. Do you consider this a bad thing? The real tragedy is that the fact he was able to ski at all with a partially healed knee was ignored while knee injuries in skiing continued escalate.

 

Hi Linchpin
How important are the intrinsic foot muscles to a skier and would strengthening them impact performance ?

Regards

Gerry

 

Just to be clear, are you talking about the moment arm the center of mass has about the ankle joint? I don't see how this concept applies to how the device can allow the user to alter the maximum arch height.

Eric

 

"asperities" I had to look that one up. Are you sure that means what you think it means? The foot has evolved for repetitive loading and unloading. One could make the case that walking during daily activities is better for the foot than complete non use. Why do you think decompression recompression is a bad thing for the foot? That's the same thing as walking.

Many different issues here. One issue is are orthtoics good. Literature says that they are helpful for some conditions. Another issue is whether an orthotic stabilizes the foot in neutral position. A lot of podiatrists believe that, but I'm not one of them, because it is quite easy to move the foot when it is on top of an orthosis.

Another issue "What this (an orthosis) does is virtually ensure the presence of a large unbalanced inversion-lateral rotation moment of force capable of applying a high transient varus thrust-lateral vertical axial rotation to the tibia against a well stabilized femur."

There is a lot to deconstruct here. Newtons 2nd law says that an unbalanced fore would cause an acceleration. In most activities, you don't see an acceleration, so this would be a balanced thrust. You should really practice some free body diagram analysis to help you describe forces. For example, looking at the tibia, body weight from above and ground reaction force from below compress the tibia. If the center of pressure is moved more medially (with a varus wedge orthotic) this will tend to increase the varus moment on the tibia. This may or may not be a bad thing depending on the starting alignment of the tibia and the femur. For example, if there is genu valgum, prior to adding the medial shift in center of pressure there will be a valgus moment on the tibia. The medial shift in the center of pressure would reduce that valgus moment. When you talk about forces and moments it is helpful to describe where the force is coming from and what it is applied to.

Another issue:
"the presence of a large unbalanced inversion-lateral rotation moment of force capable of applying a high transient varus thrust-lateral vertical axial rotation to the tibia against a well stabilized femur. Do you actually buy into this sort of nonsense Eric that rendering the ankle foot complex dysfunctional somehow makes it more functional?"

You are skipping a few steps. How does that "thingie" cause the foot complex to be disfunctional?

And finally: Yes I'm lauding the load bearing mechanisms of the foot. Most of the time they work really well. When they become overloaded pathology develops. So, excessive load is a bad thing. We spend a lot of time trying to decrease the load on the structures of the arch in injured people.

From your description, and picture, of your device, it appears that your device would apply a force to the dorsum of the foot. The device that I described, essentially a large hose clamp embedded in the ski boot, also applied a force to the dorsum of the foot. Both may make skiing better as attempted foot movement will transfer force to the boot sooner. Both could obstruct synovial fold on the dorsum of the foot. Can you explain the difference between your device and the hose clamp? Can you explain the difference in terms of forces applied to the foot? Sometimes a good patent lawyer can make something appear different from prior inventions without there being that much difference.

Eric

 

Linchpin:

I agree with Eric..I find it hard to follow your discussion here. What exactly is arch decompression-recompression? Do you have any references, other than your own, that use this terminology?

Also, you make a number of claims where you seem to indicate that you are the authority on foot biomechanics by making such statement such as "many of your colleagues appear to have bought into is the idea that the human foot works better in activities such as skiing when its joints are immobilized with some sort of form fitted liner and orthotics or insoles that attempt to stabilize the STJ in neutral". We call that a straw man argument, not factual, but rather stating inaccuracies that aren't true in order to make you appear more knowledgeable than podiatrists. Please provide references that using foot orthoses negatively affects downhill ski performance. In my clinical experience, I have never treated a skier with foot orthoses who didn't feel they helped their skiing performance.

And, please, Linchpin, we already have enough people here making claims for their patented products with unsupported claims with no references, other than their own. We don't really need to hear about the anecdotal stories of the elite athletes that you have treated with their patented product that "enabled" an athlete to win a race. These claims mean little to me and to the rest of those following along.

If you want, Linchpin, to have a discussion on the biomechanics of the longitudinal arch of the foot (which is what this thread I started should be about), then that is fine. But if you want to discuss your patented product and provide us with pure anecdotal quotes of how great your patented product is, how many championship athletes you "enabled" to win races, and how podiatrists don't know what they are talking about because they are not you.....then please start another thread...... and have at it.

 

I believe that the only credible performance claims are those supported by data from in vivo studles in which a technology, or intervention such as an orthotic, is compared to baseline data obtained from a reference such as barefoot or a technology that a participant is familiar with.

In February of 2013, I retrofit identical hockey stakes with a module employing the technology disclosed in my patent and sent the skates to the School of Human Kinetics at University of Ottawa for studies to be conducted that would compare the skates to participants’ own skates using protocols that would produce quantifiable metrics. My hypothesis was that the technology would signficantly improve loading response and time to stabilization in the stance phase of skating by at least 10%. I was advised by one of the researchers that this was unrealistic and that it was rare for tests of this type to realize more than 1 to 2% improvement. The results of the tests were presented at the ECSS (European College of Sports Science) in June 26-29 of 2013 in Barcelona, Spain. Please note that I was not involved in any capacity in the actual studies other preparing the skates and was not present when the studies were done.

The following text is from the presentation.

"Five competitive-level hockey players completed three skating acceleration trials from rest on a regulation ice hickey rink. Tekscan Inc. insoles were placed into a hockey skate equipped with a novel technology designed to optimize force transfer and control (NS - New Skate). followed by participants’ own skates (OS - Own Skates). Peak plantar force, impulse, and center of force (COF) variance (in the medial-lateral axes) were measured by the insoles after calibration to pressure levels to be observed during skating trials. Participants were instructed to start skating as quickly as possible and attempt to reach maximal speed until told to stop. There trials of the drill were completed for each of the two conditions. An in-skate pressure measurement system (Tekscan Inc.) was used to obtain force production data from subjects. Two tailed, one sample t-tests were used to determine statistical signficance between NS and OS condition. Significance level was set at p _< 0.05."

"Maximization of dynamic stability while skating is crucial to achieve high plantar force and impulse. Impulse in particular has been identified as an important performance parameter in sprinting sports as skating. Acting to optimize dynamic stability, the the higher COF variance indicates a greater ability to move the body through the stance phase of skating in a controlled manner."

As to the results study, I had been advised by one of the researchers that a quantifiable improvement of 10% was improbable and that a quantifiable improvement of 1 to 2% was be more realistic and should be expected. I will you give you a few days to contemplate what actual results of the study were. In the meantime, I would appreciate it if those who make claims for orthotics for use in ski boots or hockey skates could please post links studies or results in which the orthotic was compared to a generic flat insole.

 

Impulse is force times time. So, if one put a clamp on top of the foot that compressed the foot into the foot bed, you would expect to see increased force at the foot - foot bed interface where the techscan sensor would have been placed. So if you you had two trials that had equal impulse at the skate /ice interface you would see increased impulse at the foot/foot bed interface if there was a device compressing the foot into the foot bed.

 

Where did the patent or the protocol state anywhere about compressing the arch? it didn't. This aside, how would compressing the arch create greater acceleration? One of the researchers ran Tekscan Inc Canada. Are you impyling that he didn't know how structure research protocols? Limiting the maximum height of the arch pertains to limiting decompression. Please stop reading things into the picture there aren't there. This research and the studies done in 1991 on loading response and peak force and impulse are directly related to Kirby's paper.

 

Since I review papers for about four podiatric and biomechanics journals, I would be happy to critique your research once you have provided me with complete details of it. When someone with a financial interest in a product claims they have had great results in their research of their own product, I tend to take their promotional declarations with a grain of salt until the full details of that research is made available. People who patent things always thinks their patented item is the best thing in the world...even though it isn't.

 

Did you miss the part where I stated that my only role was to supply hockey skates for a research project at the request of one of the researchers. The studies were never discussed with me. So I did not even know what study would involve. Nor did I play any role in the design of the studies nor was I involved in any way. This issue aside, I have requested in vivo studies to support claims made by podiatrists for the value of orthotics in ski boots skates. Can you please provide links to these studies which I agree should independent to ensure they are free of bias and conflict of interest.

My technology provided a standardized interface that allowed the researchers to compare the effect of unknown constraint applied to the foot by the subject's own skates. I had no expectation of what would happen aside from early speculation after proof of concept testing initial crude prototypes which I refer as Lab Rats that got positive subject comments. The study was not intended a product. It was intended to promote a protocol that would address the inability to identify control variables which was an issue in the University of Ottawa pressures that saw significant variances in pressure that could not be explained.

I regard independent proof of concept and validation of a hypothesis for a new technology as an essential prerequiste to commiting resources to product design and development only to find out later that the concept does not produce the expected results. For this reason, when I was approached and asked to 'attempt' to design a new ski boot in 1991, I would not agree unless the company engaged scientists with expertise in the related field to provide oversight and conduct studies to validate or invalidate my hypothesis. This unbudgeted line item cost close to $140,000. Even though my hypothesis was indepently validated, it never resulted in a product. It is a very long road from an idea to product and an even longer road to a successful product regardless of the number of studies that support the concept.

I spend a large component of my time researching and reading papers, assisting racers and skiers and writing posts all pro bono. My work centers around assisting skiers to make existing ski boots and related equipment work. I am also providing links to resources such as EBFA and others with expertise in improving foot and whole body function. If and when a product I have had a role in becomes a market reality I will disclose my interests. For the time being, my interest and involvement is limited to the promotion of human performance. If this group is not aligned with this cause, I will call it a day and move on.

 

It would be helpful if you could define what you mean by decompression. You could also explain why limiting decompression would be a good thing. Where did I say anything about the researchers not knowing anything about research protocols. I was trying to explain why one might see an increased impulse with your device without seeing increased acceleration. Of course, you could stop playing games and just post what the results of the study were rather than have us guess at it. In the absence of you explaining how your device works, all we have to go on is what you have said and the pictures that you have provided. Thinking about physics if one wanted to limit the maximum height of the arch one would push downward on the top of the arch. The picture of your device shows part of the device touching the top of the arch. So can you explain how your device limits the maximum height of the arch without pushing down on the top of the foot?

 

Hi Kevin
I read your paper and was drawn to figure 6 in particular . This shows a simplified ,two part ,representation of the bony arch of the foot with the bony arch uppermost then plantar ligaments ,muscle and the finally the plantar fascia . Looking at the drawing do you think it possible that during the initial phases of gate , and as the system loads ,that the muscle between the ligaments /bony arch and the plantar fascia will become subject to compression between these two components and that this might this activate the plantar venous pump ?

I ask because if this does happen then the implications of Dr Karen Mickles present work (1) could be enormous .

Regards

Gerry

(1)Evaluating a foot strengthening exercise program to improve foot function in adults with diabetes

 

The Plantar Support of the Navicular-Cunieform Joint: A Major Component of the Medial Longitudinal
Arch
Lyndon Mason, FRACS(Orth), Eric Swanton, MBChB, FRACS(Orth), Lauren Fisher, PhD Andrew Fisher, PhD, Andrew
Molloy, FRCS(Tr&Orth)
AOFAS Annual Meeting 2018 1

 

The paper referenced above states "The major support of the distal aspect of the medial longitudinal arch (i.e. the navicular-cuneiform joint) is provided by the substantial navicular cuneiform ligament."
This is perhaps true in mid stance but may not be correct with regard to the push off phase of gate when the ligaments on the dorsal aspect of the joint provide greater support to the arch .

 

The loads on the arch are similar, in direction, and which structures are loaded, in both stance phase and after heel off. In propulsion, the dorsal ligaments are not strained by the predominant forces.

 

It strikes me that during gait the arch flexes in different directions in the sagittal plane .

When not under load the arch has a particular configuration . In mid stance the arch is more flattened . At push off , due to the presence of the plantar ligament , the arch flexes in the opposite direction as it adopts a more pronounced arched shape . It is not unlike the drawing of a bow where the belly becomes compressed and the back is under stretch/tension .

Hence , dorsal ligaments likely provide a great deal of support to the proximal medial arch during push off .

Question ;
If , during push off , the dorsiflexed position of the toes causes the medial arch to become more pronounced , does this not mean that the points of attachment of the navicular cuneiform ligament become more closely approximated than the are when the arch is not under load ? How then , during this phase of gait ,does the ligament provide support for the navicular-cuneiform joint at all ?

 

It all has to do with the direction of the load. After heel off, the forces acting on the foot are ground reaction force on the forefoot downward bodyweight from the tibia applied to the talus, and upward pull from Achilles tendon at its insertion on the calcaneus. These forces will tend to plantar flex the rearfoot and dorsiflex the forefoot. To resist those forces you need tension on the bottom of the foot and compression on the top.

If you see plantar flexion of the forefoot on rearfoot after heel off, there will be less tension in the plantar ligaments, but there will be more tension in the plantar muscles, tendons, and plantar fascia. The plantar tension, in the structures that I just named, is what causes the plantar flexion of the forefoot on the rearfoot.

The bow analogy does not work, because it does not have the same external loads as the foot.

 

Gerrard:

Are you a podiatrist? Have you ever read the papers from over 60 years ago by John Hicks and his windlass effect? Reading your questions/comments, I just thought you should do a little more background research into the classics. By the way, it is not the "plantar ligament" that causes the "arch" to "flex" at toe-off. It is the plantar fascia and the windlass effect that John Hicks first described 64 years ago that causes medial longitudinal arch raising, subtalar joint supination, and external tibial rotation during weightbearing hallux dorsiflexion (Hicks JH: The mechanics of the foot. II. The plantar aponeurosis and the arch. Journal of Anatomy. 88:24-31, 1954).

 

Kevin ,
Let's take your video . Press down on top of the structure and both sets of cords take the load . Shorten up and secure the blue cords to represent the windlass effect ,and then press down again . The pink cords (plantar ligaments ) are no longer loaded only the blue ( plantar fascia ) .

Re plantar ligament ,yes typo .

Longitudinal Arch Load-Sharing System Demonstration with Wooden ...



▶ 4:33
21 Sep 2018 - Uploaded by Kevin KirbyThis wooden model of the foot shows how the plantar ligaments and plantar fascia work together to help ...

 

The plantar fascia causes arch raising with hallux dorsiflexion, not the plantar ligaments. The plantar fascia and plantar ligaments are passive elements and can't be physically shortened.

Are you a podiatrist or a dentist??

 

Stuck Kevin ?

Re "Are you a podiatrist or a dentist??

You are well aware I am a dentist hence the specificity of your question .
Are questioning my credentials to have an opinion on a very simple wooden model ?

 

Didn't know if you were a dentist or podiatrist for sure. However, I do think I will go bother the dentists about tooth biomechanics on Dentistry Arena....

 

So moving along , I would venture further that the intrinsic toe extensors assist with supporting the ligaments on the dorsal aspect of the bones of the MLA , during push off , by contracting at this point in gait ( Zelik ) . Of course in my description of the initial windlass phase of gait (1) I stated that the contraction of the toe dorsiflexors leads to a shortening of the MLA in preparation for weight acceptance , so how can the same muscles resist foot shortening ? The answer is that the extensors produce foot shortening until the toes reach the limit of their range of dorsiflexion . Thereafter their contraction resists foot shortening .

This may all sound a bit contradictory until you consider the shatterproof ruler/ belt model I used in a previous thread :

"It does if the active tensioning component on the top (the extensor muscles ) and the passive band on the bottom (the plantar fascia ) are directly connected to each other ,in this case via their attachments the the base of the proximal flange .

As a simple thought experiment think of a flexible . shatterproof 12 inch ruler with a small roller placed at one end . Now imagine a thin leather belt lying along the underside of the ruler ,over the roller and then back along the top of the ruler .Imagine also the base of the ruler and the underside section of the belt are fixed in place in a vice of some description . Ok ,now pull on the upper free end of the belt . The ruler will curve upwards as you have indicated .

However if you start off with a ruler which is already configured in an arch shape ,similar to the foot , then you will find that the arch deepens as you pull on the upper end of your belt .It will not invert back the other way . The arch / belt system will become better at resisting forces acting the straighten out the ruler -it is more rigid .

So it is with the arch of the foot ,the extensors and the plantar fascia .​

Gerrard Farrell "

In the ruler/ belt model ,pulling on the belt ( extensor activity ) will only act to deepen the arch if the belt can continue to slide past the end of the ruler . Otherwise pulling on the belt will tend to straighten the ruler .

Ps Kevin , I look forward to posting on Dentistry Arena once you have got it up and running .

(1)
Windlass mechanism | Podiatry Arena


https://podiatryarena.com › Forums › General › Biomechanics, Sports and Foot orthoses8 Feb 2018 - So during the gait cycle the windlass mechanism is engaged and reversed twice . Going from heel strike to ... Gerrard Farrell Glasgow. scotfoot .

.

 

Here is the abstract of a recent paper from Professor Karl Zelik on the coordination of the intrinsic foot muscles during walking . I feel it fits well with my posts on this thread .

Eur J Appl Physiol. 2015 Apr;115(4):691-701. doi: 10.1007/s00421-014-3056-x. Epub 2014 Nov 25.

Coordination of intrinsic and extrinsic foot muscles during walking.

Zelik KE1, La Scaleia V, Ivanenko YP, Lacquaniti F.
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Abstract

PURPOSE:

The human foot undergoes complex deformations during walking due to passive tissues and active muscles. However, based on prior recordings it is unclear if muscles that contribute to flexion/extension of the metatarsophalangeal (MTP) joints are activated synchronously to modulate joint impedance, or sequentially to perform distinct biomechanical functions. We investigated the coordination of MTP flexors and extensors with respect to each other, and to other ankle-foot muscles.
METHODS:

We analyzed surface electromyographic (EMG) recordings of intrinsic and extrinsic foot muscles for healthy individuals during level treadmill walking, and also during sideways and tiptoe gaits. We computed stride-averaged EMG envelopes and used the timing of peak muscle activity to assess synchronous vs. sequential coordination.
RESULTS:

We found that peak MTP flexor activity occurred significantly before peak MTP extensor activity during walking (P < 0.001). The period around stance-to-swing transition could be roughly characterized by sequential peak muscle activity from the ankle plantarflexors, MTP flexors, MTP extensors, and then ankle dorsiflexors. We found that foot muscles that activated synchronously during forward walking tended to dissociate during other locomotor tasks. For instance, extensor hallucis brevis and extensor digitorum brevis muscle activation peaks decoupled during sideways gait.
CONCLUSIONS:

The sequential peak activity of MTP flexors followed by MTP extensors suggests that their biomechanical contributions may be largely separable from each other and from other extrinsic foot muscles during walking. Meanwhile, the task-specific coordination of the foot muscles during other modes of locomotion indicates a high-level of specificity in their function and control.