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Do foot orthoses weaken "arch" muscles?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Mar 5, 2005.

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  1. Craig Payne

    Craig Payne Moderator

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    How often have you heard the claim that foot orthoses are "crutchs" and should not be used as they weaken muscles etc etc .... ... well...:



     
    Last edited by a moderator: Mar 6, 2005
  2. Atlas

    Atlas Well-Known Member

    Good study...good topic.



    So much empty rhetoric is given in an adhoc manner, that I feel sorry for the lay person looking for decent healthcare.
     
  3. Atlas

    Atlas Well-Known Member

    Does this research suggest that

    a. We have under-estimated the passive structures that underpin joint position status?



    b. That over-using a muscle or asking it to function differently does not necessarily equal strength?
     
  4. Chuck Langman

    Chuck Langman Welcome New Poster

    My reply is anecdotal and relates to what I have seen in myself after wearing orthotics for just over 20 years (since I was 22 y.o.). I have a flexible flatfoot and notice that each new pair of orthotics I get (and for that matter, each set of casts) has a noticeably "higher" arch. There is however no corresponding increase in the weight bearing, unsupported view of my foot. This could account for the inaccurate observation that my foot is "weak". A lay person with no understanding of biomechanics and intrinsic bone structure could incorrectly deduce that my flat, kind of floppy foot is weak as a result of the orthotics. I feel quite the opposite, that the orthotics hold my foot in a rectus postion allowing the muscles to accomodate to a corrected position. The bone structure sadly does not follow suit and my foot pronates still when unsupported.
     
  5. Craig:

    Nice study. It would be interesting also to test the plantarflexion strength of the 1st MPJ, instead of just the lesser MPJs. I have never thought that foot orthoses weaken the foot muscles, even though this is a common question that lay-people have of orthoses. I do believe that foot orthoses decrease the muscle activity in many muscles of the foot, but improves their efficiency so that they are not working as hard but are accomplishing more for the foot.

    The medial arch supporting mechanism of the foot involves the extrinsic muscles, intrinsic muscles, plantar aponerosis and other plantar ligaments. If the muscles are weaker, then they will have a decreased ability to support the arch of the foot. However, I truly doubt that an orthosis will cause actual weakness of the foot as long as the patient is staying physically active while wearing the orthoses. In addition, I am sure that in many cases, if the orthoses allow the patient's pain to resolve so that they can become more physically active, the muscle strength may actually increase as a result of wearing foot orthoses.
     
  6. Craig Payne

    Craig Payne Moderator

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    Its also reminds of all those claims re strengthening intrinsc muscles can be used to elevate arch and stop the foot pronating ... so you don't need foot orthoses ..... that claims gets my Homer doh! award:

    [​IMG]

    The intrinsic muscles don't even start to fire until the heel is coming off the ground :p - don't matter how strong they are, its toooooooooo late :p .....doh!
     
    Last edited by a moderator: Mar 6, 2005
  7. Craig:

    Root et al show that the lumbricales are active from early midstance to mid-propulsion, the interosseous muscles are active from late midstance to nearly toe-off, the abductor hallucis muscle is active from late midstance to toe-off, the adductor hallucis is active from late midstance to toe-off, the flexor hallucis brevis is active from the middle of midstance to toe-off, the flexor digitorum brevis and transverse pedis muscles are active from heel-off to toe-off, and the quadratus plantae is active from forefoot loading to mid-propulsion (Root, M.L., W.P. Orien and J.H. Weed: Normal and Abnormal Function of the Foot. Clinical Biomechanics Corporation, Los Angeles, CA, 1977, pp. 224-252). Therefore, Root et al show that nearly all the plantar intrinsics are active before heel off, with some of them active before the middle of midstance.

    Do you disagree with Root et al in their assessment of the muscle function of the plantar intrinsics? I would be interested in any research you have that the plantar intrinsics are only active after heel-off.
     
  8. Craig and Colleagues:

    Here's an interesting article on the arch supporting function of the plantar intrinsics that I came across. The authors stated, "The results support the idea that the intrinsic pedal musculature supports the medial longitudinal arch, in addition to the bone structure and ligaments."


     
  9. Craig Payne

    Craig Payne Moderator

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    I said:
    - I did not mean the heel "off" the ground - I meant late midstance - I was not meaning heel off -- to use Howard D's terminology, I meant the time when the heel starts to unweight - thats different to heel off. I agree totally with waht Root et al said with the timing ---- we are saying the same thing.

    As the timing of muscle firing is mid to late midstance, then having those muscles strengthened to stop a foot pronating is too late - hence the doh! award to those that claim it.
    I read that when it came out - they tested the EMG of the plantar intrinsic muscles and made all their claims about what they do when the subjects were standing!!! - that equates to midstance in the gait cycle, when the instrinsics don't even fire until after then in gait!
     
  10. Craig:

    Glad to hear that we are saying the same thing regarding the temporal patterns of plantar intrinsic muscle activity.

    However, I will respectfully disagree with you that strengthening of the plantar intrinsics don't have the potential to limit subtalar joint (STJ) pronation. The plantar intrinsics probably have little effect on STJ pronatoin in the first half of stance phase but will probably have a significant effect during late midstance at reducing STJ pronation and reducing flattening of the medial longitudinal arch. Most of the plantar intrinsics are active in late midstance. Late midstance is the time when these muscles are needed most to stiffen the medial longitudinal arch against the increasing magnitudes of ground reaction force that occur during this phase of walking gait.

    I would be very surprised if muscular activation of the plantar intrinsics during the late midstance phase of gait doesn't help create a forefoot plantarflexion moment and a STJ supination moment which would tend to resist medial arch collapse and STJ pronation.
     
  11. Craig:

    A few more thoughts on this topic. The plantar intrinsics are mostly firing when the forefoot is receiving more ground reaction force (GRF) and when the plantar heel is receiving less GRF (by the way, I don't mind the term "unweighting of the heel" but the term "heel coming off the ground" is very misleading and I don't think should be used).

    If one were to model these forces along with the vertical compression force from the tibia on the talus along with the tensile force in the Achilles tendon, it would be obvious that the time during gait when there was the greatest forefoot dorsiflexion moments (i.e. arch flattening moments) would be the period from middle of midstance to heel lift (i.e. late midstance).

    With this fact in mind, then it makes complete sense that the plantar intrinsics are firing when they are needed most, when the forefoot dorsiflexion moments are increasing with a tendency to flatten the medial longitudinal arch (MLA) in late midstance. If the foot is trying to resupinate in late midstance or prevent further pronation in late midstance, then it may very much need the contributions from the plantar intrinsics to prevent pronation or accelerate supination in late midstance. Now, these muscles are not very strong or big, but they definitely are not firing "too late" to limit subtalar pronation and MLA collapse in late midstance.

    Think of an example of a foot without intrinsic muscles such as the "intrinsic minus foot". It is theoretically possible that these feet may develop Charcot arthropathy in the midfoot possibly as a consequence of these plantar intrinsics not providing good forefoot plantarflexion moment during late midstance, that would tend to decrease the dorsal interosseous compression forces across the midfoot during late midstance.

    Therefore, I'm fighting here for those little guys: the plantar intrinsics.
     
  12. Craig Payne

    Craig Payne Moderator

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    In those with diabetes, most "intrinsic minus feet" develop into a cavus foot due to the clawing of the toes from lack of plantarflexion on proximal phalanx!!!, so a weakness of the "arch muscles" does not appear to be a cause of a pronated foot.
     
  13. Craig:

    Here's some interesting research in that regard. I tend to agree with these researchers that a decrease in plantar intrinsic muscles in the intrisinsic minus foot may lead to postural instability. I still think it could lead to Charcot arthropathy.

    By the way, I thought the appearance of the cavus foot in the "intrinsic minus foot" was not actually due to a raising of the osseous structures of the longitudinal arches but rather due to the lack of soft tissue in the plantar arch, thus giving it the appearance of a cavus deformity.
     
  14. penelope latey

    penelope latey Welcome New Poster

    Hi I am currently doing some post grad research ( UTS) on the foot, posture and Pilates exercise .I am interested in the research : do foot orthoses weaken arch muscle , and would like to read the whole paper. Could you tell me where I could access it? and any other related research.
    One of my interests is the MLA and the intrinsic foot muscles both as postural "stance muscles" as well as assisting in propulsion during gait. I am curious about the discussion on intrinsic foot muscles as I successfully teach exercises that improves strength, flexibility and endurance for the whole body (including feet), would n't it be good to teach exercises for the feet to improve 'late mid stance' MLA control?
    Sincerely
    Penny
     
  15. Craig Payne

    Craig Payne Moderator

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    Sorry, we have not yet got to publishing this yet ... its on the ever expanding "to do" pile.
     
  16. parisa_arzani@yahoo.com

    parisa_arzani@yahoo.com Welcome New Poster

    hi im studing Ms in physiotherapy , i need some help about this question :is this necessary to treat a pediatric flexible flat foot with exercise ?
     
  17. parisa_arzani@yahoo.com

    parisa_arzani@yahoo.com Welcome New Poster

    my art is my hand
     
  18. Craig Payne

    Craig Payne Moderator

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    Exercises for flexible flat foot in children work really well if a weakness of the muscles is the cause (and assuming that it need treating) ... there are a lot of causes of "flat foot".
     
  19. admin

    admin Administrator Staff Member

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