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  1. #1
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    Intrinsic foot muscles .The heart of balance ?

    I recently placed a number of posts on a different part of the site under an Evolutionary heading but feel they are very relevant to the topic of footwear in as much as footwear might help or hinder the mechanisms discussed .

    Here are the posts and I would welcome any comments .

    Gerry




    POST 1
    The question I asked myself was what type of balance system can take the apparently difficult to balance , tall ,top heavy ,human phenotype and use this shape to advantage ?

    Well , first consider balancing a pencil on your finger . Its very difficult .
    Easier to balance is a long broom handle due to inertia . Easier still is the act of balancing a complete broom on your finger /palm with the broom head in the air and the end of the broom on your hand .
    So can the head of the tibia balance in this way on the talus/calcaneal unit ? I think the answer may be yes , at least for postural stability in the medio lateral direction .

    Previously , Luke Kelly (1) has shown that the intrinsic foot muscles can control foot posture including the condition of the medial longitudinal arch and ,in my opinion ,this could lead to inversion and eversion of the calcaneus, and then via the talus ,to a movement of the tibal head relative to the COG .

    Another paper has shown that the vestibular apparatus has a direct link to some of the intrinsic foot muscles showing the have a key role in balance . (2)

    A third paper (3) indicates that in the absence of strong intrinsics the extrinsics seem take on more of role in postural stability an so enlarge .

    So what I am saying overall is that the intrinsics handle small medio lateral perturbations via calcaneal positioning and with larger perturbations the extrinsics kick in to assist .

    This theory places the intrinsics right at the very heart of human balance .

    Any thoughts ?


    Paper 1 Recruitment of the plantar intrinsic foot muscles with increasing ...

    https://www.researchgate.net/.../515...nsic_foot...22 Dec 2017 - Full-text (PDF) | The aim of this study was to determine the difference in activation patterns of the plantar intrinsic foot muscles during two quiet standing tasks with increasing postural difficulty. We hypothesised that activation of these muscles would increase with increasing postural demand...


    Paper 2
    vestibular modulation of the abductor hallucis and the ... - Scholars' Bank

    https://scholarsbank.uoregon.edu/xmlui/bitstream/.../Final Thesis-Wallace.pdf?...1
    by J Wallace - ‎2016 - ‎Related articles
    explore the vestibular system. The purpose of this experiment was to determine if intrinsic foot muscles are modulated by vestibular activity and to elucidate any changes in the association between the vestibular stimulation and electromyography (EMG) responses in response to changes in head position, visual cues, and ...

    Paper 3
    Foot muscle morphology is related to center of pressure sway and ...

    https://www.ncbi.nlm.nih.gov/pubmed/28575753
    by X Zhang - ‎2017 - ‎Related articles
    Gait Posture. 2017 Sep;57:52-56. doi: 10.1016/j.gaitpost.2017.05.027. Epub 2017 May 25. Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing. Zhang X(1), Schütte KH(2), Vanwanseele B(3). Author information: (1)Human Movement Biomechanics Research ...


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    POST 2

    Look at figure 6 in the paper below . If your not sure what I am talking about in the previous post this goes a long way to explaining things . ( figure 6 shows calcaneal inversion in direct response to electrical stimulation of the abductor halluces )

    Intrinsic foot muscles have the capacity to control deformation of the ...

    rsif.royalsocietypublishing.org/content/11/93/20131188
    by LA Kelly - ‎2014 - ‎Cited by 50 - ‎Related articles
    29 Jan 2014 - We test the hypotheses that activation of the three largest plantar intrinsic foot muscles, abductor hallucis, flexor digitorum and quadratus plantae is associated with muscle stretch in response to external load on the foot and that activation of these muscles (via electrical stimulation) will generate sufficient ...


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    POST 3 --

    Further to the above , an interesting paper was very recently published , Koyama et al 2017 (below) , which looked at fatiguing the muscles of the foot and the effect this has on postural sway . They found that the exercises reduced some aspects of postural sway .
    The authors stated -

    "This study revealed that fatiguing foot muscle exercises decreased foot muscle strength and altered postural sway during standing. Interestingly, the fatiguing foot muscle exercises decreased the COP range and velocity while standing compared with the pre-fatigue conditions. The decreased foot muscle strength after the exercises was not associated with changed postural sway during standing after the exercises ".

    What makes this paper so interesting is that the exercises used in the study would have fatigued the extrinsic foot muscles but not the intrinsics ( calf raises and toe curls do not target the intrinsics and a toe grip dynamometer measures extrinsic toe flexor strength )

    Contrary to the interpretation of the authors I believe this paper may show better postural stability with less extrinsic foot muscle input and greater reliance on the intrinsics .

    Paper
    Altered postural sway following fatiguing foot muscle exercises - PLOS

    journals.plos.org/plosone/article?id=10.1371/journal.pone.0189184
    by K Koyama - ‎2017
    7 Dec 2017 - The activities of the intrinsic and extrinsic plantar muscles contribute to postural stability during upright standing, especially in the single-leg standing [9]. Foot muscle strength is considered to be one of the important essentials that provides postural control while standing [10]; however, the relationship between foot muscle ...







    Last edited by Gerrard Farrell; 01-18-2018 at 12:35 PM.

  2. #2
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    Re: Intrinsic foot muscles .The heart of balance ?

    With regard to the above , Professor Chris Nester has just started his own blog site . In one of his articles he states -


    "The foot is only ever a pure mechanical structure when it is detached from the control system. Have you ever held a fresh cadaver foot? It’s quite difficult to make the foot stand normally or simulate ground contact in a way you would recognise as “gait”. It just flops about and is quite unwieldy. It is not what you see in clinic or when you take your shoes and socks off.
    The foot is therefore never a purely mechanical structure and it is always under some level of intelligent control."


    Exactly . The foot is designed to be unstable especially in the rearfoot area . Unstable that is until you add in the intrinsic and extrinsic musculature and neural control . Once you add these in to the equation , the narrow heel of the human foot makes balancing the body above easier .

    His blog site can be found here - talkingfeet.online/2018/01/04/why-am-i-blogging/ … via @ProfChrisNester

    Actually , to be fair ,this is exactly the type of thing Professor Irene Davis has been going on about for years . Just not the short foot exercise please !

  3. #3
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    Re: Intrinsic foot muscles .The heart of balance ?

    For some time it has been the view of a number of researchers that both the intrinsic foot muscles and the extrinsic foot muscles contribute to balance but by different modalities . That the extrinsic foot muscles affect balance by altering the centre of pressure under the foot is well know but the exact contribution of the intrinsics has been harder to nail down .
    The previous posts in this thread outline the mechanism by which I believe the intrinsic provided fine tuning of balance and postural stability .A fine tuning system within a larger overall system if you like .

    Gerry

  4. #4
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    Re: Intrinsic foot muscles .The heart of balance ?

    Extract from thread on podiatry arena-

    "Practical implications of the balancing effects of the intrinsic action on "talocalcaneal stack " ? With regard to acquired pes planus (flat feet ) , a medial arch support will restore the vertical component of the talocalcaneal stack allowing ,amongst other things , a better intrinsic /calcaneus balancing mechanism leading to better fine control of postural stability and stronger intrinsics . That is what seems to happen in these cases . "

  5. #5
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    Re: Intrinsic foot muscles .The heart of balance ?

    A paper (1) was recently published which looked at the role of two of the intrinsic foot muscles and balance .Here is the conclusion .

    "The findings of this study demonstrate that the vestibular system is able to modulate activity in the abductor hallucis and abductor digiti minimi during standing. This experiment extends the previously reported operational bandwidth of coherent frequencies in the MG (0-20 Hz) (Dakin et al. 2007; Dalton et al. 2014) to intrinsic foot muscles. Elevated cortical demand and lack of visual input increase the corrective response to a vestibular error signal at predominantly lower frequencies, indicating that there are likely different origins of the short- and medium-latency responses. The abductor hallucis and the abductor digiti minimi are likely important contributors to upright standing balance control and they are capable of dynamic vestibular responses which can be modulated by other sensory feedback as well as by cortical activity. "

    (1)
    vestibular modulation of the abductor hallucis and the ... - Scholars' Bank

    https://scholarsbank.uoregon.edu/xmlui/bitstream/.../Final Thesis-Wallace.pdf?...1
    by J Wallace - ‎2016 - ‎Related articles
    explore the vestibular system. The purpose of this experiment was to determine if intrinsic foot muscles are modulated by vestibular activity and to elucidate any changes in the association between the vestibular stimulation and electromyography (EMG) responses in response to changes in head position, visual cues, and ...

    Gerrard Farrell

    Glasgow

    scotfoot, Today at 10:26 AM

  6. #6
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    Re: Intrinsic foot muscles .The heart of balance ?

    So to summarize the thead , we evolved from a gibbon like ancestor which learned to walk on feet best suited for brachiation . The divergent first ray would have given a big toe that resembles the thumb of our hand and this would have helped with mediolateral balance during upright walking .

    Committing to terrestrial bipedalism would have led to the first ray coming into line with the rest of the foot and the formation of the "talocalcaneal stack " would ,amongst other things ,have allowed the muscles of the hallux and the associated neural mechanisms to continue to contribute to mediolateral balance whilst still allowing a foot with a non divergent first ray .
    Last edited by Gerrard Farrell; 01-24-2018 at 04:09 AM.

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