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Fatigue of the plantar intrinsic foot muscles increases navicular drop.
Headlee DL, Leonard JL, Hart JM, Ingersoll CD, Hertel J.
J Electromyogr Kinesiol. 2007 Jan 5

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Related threads:
Shock absorption when fatigued
Muscle fatigue affects tibial strain
Muscle fatigue as factor in stress fractures

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This brings to mind a little discussion that Craig Payne and I had nearly two years ago Do foot orthoses weaken "arch" muscles? about whether the plantar intrinsics can help control pronation in the foot. Certainly, the plantar intrinsics are important, but are only one of the structures that help increase medial and lateral longitudinal arch dorsiflexion stiffness during weightbearing activities. The study listed above further supports the concept that the plantar intrinsics help prevent medial longitudinal arch flattening during weightbearing....however, certainly are not the only structures responsible for preventing medial longitudinal arch flattening in the human foot.

We must stop thinking of the medial and lateral longitudinal arches of the foot as static structures! We must start thinking of the medial and lateral longitudinal arches of the foot as types of "leaf springs" that can have variable spring stiffness depending on their morphology and the mechanical characteristics of the tensile load-bearing structures (i.e. muscles, tendons, ligaments) that govern its mechanical behaviour under load.

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Kevin

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e-mail: kevinakirby@comcast.net

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This topic is rather dear to me like one of those ideas that seems to "fit" into what seems to have been happening in the feet you've been looking at and playing with for too many years.

It's good that there is some research indicating that as the intrinsic foot muscles fatigue, the foot weakens and other structures are placed under more stress -
sounds logical. The intrinsics probably fatigue in feet for a number of reasons (which is another topic) I generally find triggers in many intrinsics in the classic fasciitis foot and expect that intrinsic failure precedes the fasciitis.
It certainly helps to treat them by releasing triggers and giving them some strengthening exercises.

Cheers
Shane

I absolutely agree!


How does this concept fit with the idea of using rigid orthotics (in STJ neutral or otherwise)? If we treat the foot as a shock absorber comprised of several structures to attenuate force and excessive pronation being the condition where the forces acting on the spring being too much for it to effectively damp, is blockading the process altogether the way forward?

For me one of the appealing aspects of the SALRE model is the concept of balancing forces rather than shutting down the mechanism altogether.

And yet orthotics which present graduated resistance to the MLA via the use of “soft” or "springy" materials, referred to rather dismissively as “simple” insoles are often considered inherently inferior to their butch carbon fibre cousins.

What say you all?

Regards

Robert

Orthoses stiffness is not defined by the material type. Thick "soft" material may = thin "butch" cousin.

Is rapid resistance better than graduated resistance? Don't know but from viscolelastic point of view may well be.

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I would have thought thin butch won't compress at all where thick soft will provide and increasing amount of resistance the more it is compressed.

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As Simon pointed out, there is a lot of variability in orthosis stiffness that may due to multiple factors. Sometimes I design foot orthoses with a thin polypropylene shell to allow it to have maximum flex and rebound under load whereas, other times, I may use thick polypropylene orthoses with a plantar filler to make the orthosis as rigid as possible. It all depends on the patient's foot, symptoms they are experiencing and the activity they will be using the orthosis in. I don't like composite-shell orthoses (e.g. "carbon fiber??") due to the inability for me to modify them (i.e. grind them) in the office and their inability to accept a rearfoot post that is not only durable but that also doesn't shear off or delaminate over time.

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Kevin

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Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

Interesting discussion...
(1) Regarding the role of the shell vs EVA orthosis, I almost always use a shell not because of greater 'control', but rather because I feel it is more precise. The level of control is determined by the prescription more than the material characteristics-
I ask this question... can you make a shell orthosis that does not give much control? or to use different terminology, 'doesn't actually do that much'.
I would suggest there is a much wider range of effects that may be achieved with a shell, which may then be easily repeated in the future (by repressing). An EVA device is more difficult to replicate, it's characteristics can change more as it is wears, and it is 'shank dependent'.

2. This study suggests that muscle strength does have a role to play in the characteristics of the arch. If this is the case, how to we maximise strength? Or perhaps minimise weakening? or minimise fatigue?? Is has been suggested that an orthosis can cause the plantar instrinsics to become weaker (although Craig Payne has shown this not to be the case). I would put the alternative idea that a well designed orthosis should minimise weakening by allowing the plantar intrinsics the work in a better functional position, or possibly protect them from high repetitive forces that they are not able to cope with.
Perhaps this is another negative of a device that does not allow, or encourage, first ray function.
Other thoughts??

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http://www.podiatry-arena.com/podia...read.php?t=1197

Thanks for the link Simon, interesting thread. There are obviously a finite number of discussion topics which keep coming around. For those of you who've been on this forum longer than me, sorry if this bores you.


Quote from Craig P in Aug 2004

A very valid point. Regardless of whether you like "Soft" or "hard", shank dependant or non shank dependant thin composite shell or polyprop i am always highly suspicious of anyone who only issues one type of orthotic for everyone! (can we think of anyone like that )

What do you think of acheiving flex and rebound by the use of compression of an elastic material as opposed to flexion of a thin shell? I'm thinking crash mat versus trampoline. Which i suppose would make muscular control bungee jumping.

As i said, sorry if this is going over old and boring ground for y'all but i really value these opinions.

Respectfully

Robert

There is indeed nothing new under the sun, but having new minds approaching an old topic adds depth and dimension viz no need to be sorry.


I understand the point you make here Robert. However, playing Devils advocate; lets say a practitioner dispenses identical devices to all his patients, will those identical devices function the same in all patients? In other words the function of the device is itself dependent on the function of the individual. There are so many factors at play here that once placed inside a shoe identical devices cease to be identical.

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Now THATs and interesting idea. Have to think about that one.

If a GP prescribes pethadine to every patient who walks in the door, most will experience an improvement in symptoms (and the rest will go into their diabetic coma's happy). However...

Respectfully

Robert
Learning and ruminating

This is an interesting discussion on orthotic therapy with particular emphasis on materials used. I could get my teeth into it even though it somewhat covers old ground.

I nevertheless have to get over feeling like I'm from another planet and even more that I'm a grumpy old man.

It's funny how research that is into the fatiguing of the Abductor Hallucis leading to incresaed navicular drop in standing, is for pods all about orthoses. The patient walks in the door and within 20 seconds the pod is thinking: will I use 270EVA or 350EVA (or maybe will I use 270 or 270?).

Probably I'll be ignored or ridiculed, but I think that this research topic might generate other discussion. Fancy that Abd Hall fatiguing causes a lowering of the arch! Don't remember that in my training. Does it have a role in eccentric loading of the forefoot and as it fatigues that puts more load onto the fascia or Tib Post etc? Why would it fatigue normally anyway. Maybe it could be strengthened and other symptoms would resolve?

I've got a few opinions and would love some others. Really! I'd also like to request that contributors up to now don't take my comments personally - I almost got into the materials discussion, it's a fine topic for us pods, it's just in general as a profession I think we may become fixated on too few modalities.

Maybe some intrinsics weaken as a result of types of footwear and flat surfaces and not because of a lack of orthoses?

Cheers
Shane
PS I'm involved in a lab - not anti orthoses by any means

Shane

Some interesting and Challenging ideas.

By all means share your opinions. I would like to think that even if we don't agree with one another much (most? all?) of the time we are all eager to expose ourselves to new ideas. I certainly am. Even those concepts i fundamentally disagree with are useful because they make me think WHY i disagree with them. Whilst the debate is often robust we should never be afraid of it. Even some of the most left field ideas which have passed through many of which were almost universally rejected caused some of the most fascinating and stimulating debate i have seen!

I'm not exactly sure what point you are trying to make Re the AB HAl fatigue but if you want to clarify your viewpoint we'll talk about it and maybe all learn something. And you'l generally find that most people don't take things personnally unless you get personal. Just don't start Referring to Mr Kirby as and i'm sure we'll get on fine! Whatever happened to Daflip?

Bring it on.

Respectfully

Robert

How can they say this??? According to the abstract, they did not test the extrinsic muscles. I do get this journal but it is not in the print edition. I would be curious to read the methods carefully. It could very well be that the effects are coming from the extrinsics and the intrinsics, although showing fatique, don't have much effect either way.

Nick

Its only available online as prepublication. It will be in a subseqent printed edition. So many journals now have publication backlogs, that they are releasing stuff early online.

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Shane,
I understand where you are coming from- There are many practitioners who will always look at each patient as an orthotic case, (and there are those who would suggest that I might be one of them :) )The most important thing, I feel, is that cases are rarely black and white, and only one modality works on its own.
I come from a clinic where I have had a large number of skilled physios who know much more about soft tissue therapy than I do- it is certainly a component of my skills I would like to improve- therefore I tend to utilise them, and in return they utilise me! With this situation you are likely to end up with a much more holistic treatment, and ultimately the best patient outcome.
When you say
I couldn't agree more...
But these are factors which are difficult to control for each individual- We can advise on footwear, but we can't make people walk around on irregular surfaces- it is a modern day problem. It is my opinion that at the end of the day an orthotic is an adapter for each individual's foot to be able to function as 'our maker intended' (that's another debate...). The key point here is that it is an individual thing- the benefite may be massive for one person, but subtle for another.
Working from the results of this study, we could say that we want to strengthen the plantar intrinsics... or we could decrease the load so they don't get as fatigued... I think the best result is likely if we can do both!
Invariably what happens, however, is that an orthosis is likely to give an immediate effect, and therefore the patient is less likely to follow through with strengthening work.
Perhaps the same could be said with immediate effects of trigger point therapy- they might get great improvement, but once they are out and repetitively loading their foot on a flat surface again, are they not likely to have the same problems again???
Good stuff to get the mind ticking!
Cheers
CT

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As I said to Robert previously in this thread: "there really is nothing new under the sun". The research referenced at the top of this thread merely re-inforces the findings of: Fiolkowski, P. et al: Intrinsic pedal musculature support of the medial longitudinal arch: an electromyography study. The Journal of Foot and Ankle Surgery, Volume 42, Issue 6, Pages 327-333

Discussed here: http://www.podiatry-arena.com/podiat...tar+intrinsics

This newer research is interesting when we compare this to some of the findings of early pioneers of EMG of the foot muscles:

Mann RA & Inman VT: Phasic activity of intrinsic muscles of the foot. J Bone Jt Surg [Am].: 46-A: 469-481, 1964

Gray EG,Basmajian JV: Electromyography and Cinematography of Leg and Foot (“Normal” and Flat) during Walking. Anat. Rec. Volume 161, Issue 1, Pages 1-139 (May 1968) (Full text here:
http://www3.interscience.wiley.com/c...ssue/109881173)

Abstract
Electromyography with fine-wire electrodes and special equipment for synchronized motion pictures were used to study six muscles of the leg and foot during walking in five different ways in ten normal and ten flatfooted subjects. Detailed analyses and comparisons of the two groups are described and discussed.
Tibialis Anterior has two peaks of activity at heel-strike and toe-off of the stance phase; is inactive during mid-swing and middle of the stance phase; is active at full-foot in flatfooted subjects, and generally more active during toe-out and toe-in walking. Tibialis posterior is inactive through the swing phase. In flatfooted persons it becomes activated at heel-strike and more active at full-foot during level walking. The toe-out position reduces its activity. Flexor hallucis longus is most active in mid-stance; during toe-out walking, activity increases in both phases, generally being more active in normal persons. Peroneus longus is most active at mid-stance and heel-off and generally more active in flatfooted persons. Abductor hallucis and Flexor digitorum brevis are generally more active in flatfooted persons. An important regular pattern of inversion and eversion during the walking cycle is described. Contingent arch support by muscles rather than continuous support is the rule, muscles being recruited to compensate for lax ligaments and special stresses during the walking cycle.

For an alternative to orthoses centred approaches to therapy try: http://www.aptei.com/articles/pdf/IntrinsicMuscles.pdf

One of my favourite topics and still very much under explored. , double

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I apologise in advance for asking a dumb ass question which i should probably be able to work out for myself.

Right, so when the Ab Hal is fatigued the navicular drops.

Which kind of makes sense if the AB Hal has a role in controlling MLA height.

If the Ab Hal is working harder, how long will it need to do that before it becomes as strong as it will get? Surely the increased activity will strengthen it more effectivly than any exercises.

From this two questions arise

1. How to we reconcile the concept of weak intrinsics being a cause of lowered Navicular if a lowered navicular INCREASES Ab Hal activity? Will not the increasing level of activity as the Navicular drops exert a homeostatic effect and stop the progression of the drop?

2. What exercises can we give which will strengthen the Ab Hal / intrinsics more than an increased level of activity with every step they take? Will picking up pencils really make that much difference?

If you have a patient with an active painful pathology they want to be made comfortable as quickly as possible. Strengthening muscles (IF it can be done with exercise and IF it would make a difference anyway) would take time. As Craig T points out Orthotics are more likely to work more quickly and make the patient disinclined to do strengthening work after they are comfortable.

And a final thought. If a flat foot has an increased level of activity in the Ab Hal, will using an orthotic (making the foot not flat) decrease the level of activity (and therefor over time the muscle capability)? Whilst it seems logical to me it contradicts this http://www.podiatry-arena.com/podia...ntar+intrinsics study.

As you say Simon, very interesting stuff! I have very few answers and a ton of questions!

Regards

Robert

"ignorance is the first step on the road to knowledge"

Well, go away for a few days and so much happens on this thread that I'm not sure where to begin, so will generalise for now with some observations.

We have all seen the hypertrophied Abd Hal, this is often painful to palpation, if not a part of the expressed painful arch. This one will have active trigger points and the symptoms may also include referred pain along the lower medial and medial inferior calcaneus. This hypertrophied Abd Hall is common in pes planus. Keep an eye out for it.
Orthoses are often uncomfortable at the medial heel and where contacting the Abd Hall. If you ask for activation of the Abd Hall there is usually little effect or if any it fatigues very quickly. Dry needling for release of the TrP's usually results in an observable decrease in it's size.

One surmises that the hypertrophy was caused by the scenario you mentioned Robert in question 1. ". How to we reconcile the concept of weak intrinsics being a cause of lowered Navicular if a lowered navicular INCREASES Ab Hal activity? Will not the increasing level of activity as the Navicular drops exert a homeostatic effect and stop the progression of the drop?" To which I'd reply that I think it does, hypertophies until it can't do any more, develops triggers and quits, at which point navicular may drop, and stay dropped/ In the experiment the Abd Hall was just exercised until it fatigued for the same result. The process is just a bit more complicated in real life.

This is how it 'seems' to me and enough for one posting. What great questions!!

Maybe intrinsics can be 'weak' due to lack of use 'hypo' or from overuse:'hyper'. You can see this in Tib Ant also.

Cheers
Shane

I'm inclined to agree with Shane, as are others:
"Even with maximal muscular participation, the capability to meet the valgus torques imposed on the foot is limited, providing a strong rationale for the careful selection of footwear and the addition of added support" Perry J:Anatomy and biomechanics of the hindfoot. Clin Orthop Related Res 1983; 177: 9-15

Also of note here is that as the various joint axial positions alter in response to arch lowering the ability of Abd Hallucis to generate moment which would result in arch raising may be compromised, so while the EMG data tells us the muscle fires for longer, in reality it may generate less "arch lifting" torque over this period. Or, perhaps the increased phasic activity is more like endurance training (repeated reps, same load) than strength training (increasing load, low reps)? Just a thought.

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Simon makes an excellent point here. A decrease in medial longitudinal arch height will decrease the ability of the abductor hallucis to generate forefoot plantarflexion moments (i.e. arch raising moments) with contractile activity. So, unless we know what the tensile force is within the abductor hallucis muscle and also know the geometry of the medial longitudinal arch at the instant the force is measured, we will have very little idea of how much forefoot plantarflexion moment the abductor hallucis is generating with its contractile force. In other words, if the medial longitudinal arch is very flat, the abductor hallucis may be contracting with 100 N of force and be generating 0 Nm of forefoot plantarflexion moment due to its 0.00 m moment arm at the midtarsal-midfoot joints!!

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Sincerely,

Kevin

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Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
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Makes absolute sense looked at like that.

Which leaves the questions,
1-
If the mechanics of the flatter foot render the Ab hal impotant (KK as always managing to express a difficult concept in a way that makes it seem simple) does the study of intrinsic muscle function exist solely in the realm of diagnostics and research or can it be used directly in treatment?
(i know effective diagnositics are integral to effective treatment but you get the idea)
2-
Is there anything that we can do to effectivly strengthen them? Taking Simons point about strength training "(increasing load, low reps)" How would we use that as part of a treatment plan (very small weights? )

3-
If we DID manage to strengthen them sufficiently, would that be enough to correct the problem WITHOUT useing orthotics as well?

4-
If the answer to 3 is no, is there value to trying to strengthen muscles?

Thanks for everyones input on this thread. I'm enjoying it a great deal!

Regards

Robert

Any new information garnered by meaningful research may eventually lead to improvements in treatment. All it takes is someone to understand the research, think about its implications relative to the mechanical function of the foot and lower extremity and the pathology of interest, and apply it to the patient with careful observation. This is how new treatments are designed, implemented and, eventually, become the standard treatment of the medical profession.

Exercise certainly has the potential to strengthen the plantar intrinsics just as exercise will strengthen any muscle. The problem is expecting the plantar intrinsics, which have limited cross-sectional area and limited strength potential even with strengthening exercises, to try and perform a job that they will never be capable of. That is why foot orthoses are so necessary, in many cases, to assist the plantar intrinsics in the producing effective forefoot plantarflexion moments.

In some mild cases, yes. However, in many cases, orthoses are necessary. See answer #2.

I don't routinely have patients strenthen their plantar intrinsics but do encourage weightbearing activities that will tend to increase the strength of the plantar intrinsics. Most of my patients would more benefit their foot problems by losing 25-100 pounds in body weight than by strengthening their plantar intrinsics!!

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Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

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I hear that! Love it when a 30 stone jogger with heel pain comes in and the first thing they say is "don't tell me it's my weight". None so blind.


Absolutely agree. I was thinking more in an immediate sense. In a general sense anything which improves out understanding of how the body works has the potential to be useful and should be explored (as we are doing)

.
My concern with exercises is that the muscles in question get a rather significant amount of activity during walking, usually against resistance occasioned by gravity. Given that they do that every day, sometimes for hours, how much difference will ten minutes picking up a pencil with your toes make?

What kind of exercises do people use?

Regards
Robert

Dear All

Quandry. Muscle fatigue navicuar falls.

I thought the foot acted as a truss.

A truss is designed to become more stable as load increases...yes?

If so, how come the foot flattens? Do we not have a truss, but just a totally dynamic ever force changing structure with torque converters?

More on exercise later in the year when I will be publishing data from patients with plantar fasciitis.

Musmed
www.musmed.com.au

This sounds very much like a haiku. Few too many syllables but reads like one!

A truss does indeed become more stable as load increases but there are some significant differences. Firstly a truss is allways a closed unit (usually a triangle. However the lower "side" of the foot truss is represented by tendons and fascia which can stretch with increasing load, thus the lever arm increases as the navicular falls increasing the tensile stress on the lower side of the truss etc etc. I refer you to Simons post on http://www.podiatry-arena.com/podiat...ght+experiment

This is from good old wikipedia and expresses rather well how the structue of the truss stresses materials in the way they are best able to withstand. because the foot is not particularly triangle shape there are considerable shear, bending and other forms of stress.

But hey what do i know! Engineering not my strongest suit. I could be wrong anyone want to correct me?

"Foot flattens in space
The Stresses cause destruction
Bridges are stronger"

Haiku is a beautiful art form :)

Regards

Dear Robert

Bewdafully put.

Maybe I was under some stress
to bend the truth
but the tension prevented me

I like the idea that things are all compression or all tension.

But fascia is not in this state. It has a 22 sided body that has both compression and tension that cancel each other out - as I understand it.

The size of the drop measured would far exceed the 3% plastic deformation of ligaments before the point of no return. Something else is happening.

As regards to triangles not there. I will beg to differ. Basically as I continue to map the body especially in reationship to non loading bearing joints we are just triangles.

Why? because nature is lazy (but very very clever). If you have a triangle you have three receptors. When you have three you can map any point inside the triangle and thus you know where you are.

A square, rhombus, no hope.

Ever thought that just getting home at night is one of the most complex things one can do?

musmed
www.musmed.com.au

ps i liked your haiku

Musmed

The foot moves three ways
The triangle sways outward
dimensions are four

You are, of course, correct. My bad, i was oversimplifying the planter tensile structures as a whole.

As you say The drop of the navicular cannot be caused by the foot elongating alone. The something else is, or course, the triplanar collapse. This is where the 2d modeling of the foot becomes insufficient.

Also this assumes that the PF was at maximum tension in the initial sample of the study.


Thats a really rather interesting way of looking at things!

Regards
Robert