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The human flexor hallucis brevis can support the weight of an elephant .

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Feb 3, 2019.

  1. scotfoot

    scotfoot Well-Known Member

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    The human flexor hallucis brevis can support the weight of an elephant .

    Or at least it can in theory if dissected out , placed at the bottom of a water tight cylinder and plunger arrangement and then used to support the elephant as a substantially incompressible fluid .

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  2. scotfoot

    scotfoot Well-Known Member

    Previous work from Luke Kelly and his associates has demonstrated that the intrinsic foot muscles are most active during peak ground force and push off (1) .

    In a more recent paper (2) it was found that the intrinsics did not provided significant support to the arch as represented by the Cal-Met angle .

    So I believe it is entirely plausible that the intrinsics act both to assist with push off and to redistribute forces within the bony arch of the foot during earlier stance .

    Active regulation of longitudinal arch compression and recoil during ...


    (2) The functional importance of human foot muscles for bipedal locomotion
    Dominic James Farris, Luke A. Kelly, Andrew G. Cresswell, and Glen A. Lichtwark
    PNAS January 17, 2019
  3. scotfoot

    scotfoot Well-Known Member

    Is there any evidence that the some of the intrinsic foot muscles act as a viscoelastic core within the foot ,whose viscoelasticity can be altered by muscle activation levels ,and the compression of which , between the lengthening arch of the foot and the spanning plantar fascia , helps to spread load within the bony articulations of the arch preventing the generation of harmful shear forces at heavy loads ?

    Yes . The plantar venous plexus and the pressure generated therein .

    The foot evolved from a grasping structure into an arch structure .The arch is made up of bones of varying lengthens held together by ligaments .

    If you build yourself an arch made of bits of lego held together with sticky tap its not much of an arch . Add a string tie beam (the plantar fascia) and things get better , but the structure is still susceptible to buckling under load .
    In the foot , if you add a viscoelastic core between arch and fascia you are in business with the core providing force redistribution , at high loads even if the core is not resisting whole arch compression .

    I believe this mechanism fits with the findings of Dr Kelly and Co , if not with all of their rational .
  4. scotfoot

    scotfoot Well-Known Member

    In my opinion and in light of the recent work by Kelly and associates , the systems outlined by me a few years ago in the following quotes , are now likely to be correct in most regards .

    Note also that the plantar venous plexus is much more important to lower limb circulation than experts have hitherto supposed .

    Hi Casey
    Might it be ,during early stance when the bony arch of the foot lengthens and the plantar fascia becomes tensioned ,that the passive intrinsic musculature located between the arch and the fascia becomes compressed between the two structures (transverse passive compression ) providing support to the arch and a reduction in the shearing forces between the articulating bones of the foot in the midfoot area ?
    Also ,might it be that the intermuscular pressure generated through the transverse passive compression of the foot intrinsics ,in the way outlined above , provides the primary force for the compression and empting of the vessels of the plantar venous arch ?
    I understand and largely agree with the ?foot core system ? outlined in your article ( although I have to say I am not an expert in either foot anatomy or physiology) but believe that the intrinsic muscles of the foot also act as the core of the foot in a much more literal sense .

    Kind Regards


    4. Gerrysays:

    November 16, 2014 at 11:22 am

    Hi Casey
    As outlined above I wondered if the plantar intrinsic foot muscles (PIFM) located between the bony arch of the foot (BA) and the plantar fascia might be subjected to passive transverse compression (PTC)when acted upon by these structures during early stance .
    I also wondered if ,during mid to late stance when the PIFM are active ,an increase in the stiffness of the ?intrinsic core ?might provide even greater support to the BA and its articulating joints .
    So the question for me is -Is there an increase in the intra and inter muscular pressure in early stance and can this be attributed to PTC ?
    An in vivo study to investigate this might involve indwelling intramuscular pressure sensors but why go down this road when such a sensor may already be in place in the form of plantar venous plexus (PVP).
    So can the PVP be looked at in this way? Is the pump emptied by inter-muscular pressure or by stretching and necking down ?
    Since the veins of the plexus are elastic longitudinally and viscoelastic transversely the effective emptying of the PVP by stretching and necking down is ,in my inexpert view ,unlikely .
    So if necking down is not the mechanism of PVP emptying then the pump must be emptied by increased inter- muscular pressure .But what cases this ?
    If the pump empties in early stance when the plantar intrinsic muscles are not activated then the pressure must be created by stretching of the PIFM or by PTC.
    A study by BJ Broderick et al(1)showed that the PVP is emptied when a standing individual performs toe curls so it can be inferred that inter-muscular pressure is increased when the muscles become activated and contract. I believe that it is reasonable to think that inter-muscular pressure is therefore not increased when the same muscles become less active and return to their original more lengthened positions .
    So, in my opinion, it is most likely that in early stance the PVP is emptied by the passive transverse compression of the ?intrinsic core? and indeed that the existence of a functioning PVP confirms the existence of a significant level of PTC . I also think it likely that the pressure generated in the pump reflects the inter and intra-muscular pressures generated within the ?intrinsic core? and hence the pressures generated at the interfaces between the core and the plantar fascia and BA .

    I would welcome any comments on the above

    Kind regards

    Gerrard Farrell

    Ref (1) Broderick et al -Venous emptying from the foot ; influences of weight bearing ,toe curls,electrical stimulation ,passive compression and posture 2010
  5. scotfoot

    scotfoot Well-Known Member

    Re the second sentence in the above post "Note also that the plantar venous plexus is much more important to lower limb circulation than experts have hitherto supposed ."

    In a running individual surely the blood being moved out of the foot is not just being moved out and upwards against gravity , but centripetal forces and the "centrifugal affect" also provide an impediment .

    Similarly , the calf muscle pump also has to overcome such forces and this may play a major role in venous regurgitation in incompetent veins . Cardiac preloading may also be affected by centripedal forces and the centrfugal effect .

    Any thoughts ?

    Rob ?
  6. scotfoot

    scotfoot Well-Known Member

    As an example , imagine two squeezy bottles of thick sauce , for example tomato . Now make sure you have clear holes in their tops of about 1-2 cm . Then imagine securing one inverted bottle to your leg( hole down ) just above the ankle ,whilst the second bottle is inverted and used a control .

    Now imagine running as fast can . The static bottle will take an age to empty whist the bottle around your ankle will empty ,very messily ,in a few second .

    You can see the forces involved and understand that , whilst running , venous blood will have great difficulty leaving the foot without the explosive aid of the plantar venous plexus .

    Note ; I used the word " imagine" a lot in this post because the sauce will go everywhere if you do the experiment for real and so slipping , and thus injury , might be a possibilty . I do not recommend trying out the experiment for real . It should be possible to imagine things without the need for sauce dripping from lab ceiling .

  7. scotfoot

    scotfoot Well-Known Member

    Further to the above this from a thread on Biomch-l from the last few days -

    Re: Centripetal forces and the calf muscle pump

    Many thanks for the above .

    During gait on a running track ,the foot undergoes periods of rapid acceleration , even more rapid deceleration and not moving at all if we take the track as a reference point .

    For example let's say we take an individual walking at 1.5 m /s . That is to say the persons COM is moving at 1.5 m/s relative to the track . The standing leg (reference leg ) will be on the track and not moving at all so we have a "velocity gradient" along the length of the leg as the body moves forwards .

    So now let's say the swing foot touches down on the track and the reference foot starts to clears the track .
    The reference foot was moving at 0m/s but must quickly accelerate to catch and pass the body . So let's say it goes from zero to 3m/s in a third of a second . This acceleration of the reference leg and foot is likely to generate substantial centripetal forces and "centrifugal effect" making venous return more difficult than if it were merely against gravity .

    So the reference foot now comes past the body and just as it touches the ground , it decelerates very rapidly to zero ,and then to 1.5 m/s in the opposite direction to the COM so again we have higher centripetal effect .
    I don't have the math's to work this all out so resorted a bottle of HP sauce strapped to my ankle .

    . In a quite part of Glasgow I then walked a number of steps and found that the thick sauce did indeed flow much more rapidly out of the bottle during the swing phase of gait and at the end of the swing phase in particular , as the foot rapidly decelerates . (It should be noted that even although the now track bound foot is not moving relative to the track it is moving at 1.5m/s relative to the body and so centripetal forces are still being generated )

    I do not recommend this experiment at all as it causes a real mess ,there is a danger of slipping on the sauce and my training shoes are now in the bin .

    Ton , could you once again put some figures on the above ? It may be that the way venous return is viewed needs to be changed .

    Gerrard Farrell [​IMG]Senior Member
    Join Date
    Dec 2015
    Wilton Street Glasgow


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