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The extensibility of the plantar fascia influences the windlass mechanism during human running

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Feb 27, 2021.

  1. scotfoot

    scotfoot Well-Known Member


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    I am absolutely baffled by aspects of this paper, which contains material which seems to me to make no sense .
    The specific part of the paper I am referring to is the part which deals with the windlass at initial contact .

    It has long been recognized that in the habitually shod western foot ,the toes are dorsiflexed at initial contact and that during weight acceptance the plantar fascia is does not initially lengthen as the toes plantar flex . In fact I think that Caravaggi et al 2009 found that there was a lengthening of the plantar fascia at initial contact .
    In Welte et al the authors suggest that having the toes initially dorsiflexed protects the PF from strain and instead sees the plantar ligaments load preferentially . But why would having the toes dorsiflexed be any different than neutral ?

    The extensibility of the plantar fascia influences the windlass mechanism during human running

    Lauren Welte,
    Luke A. Kelly
    ,
    Sarah E. Kessler
    ,
    Daniel E. Lieberman
    ,
    Susan E. D'Andrea
    ,
    Glen A. Lichtwark
    and
    Michael J. Rainbow
    Published:20 January 2021https://doi.org/10.1098/rspb.2020.2095
    Abstract

    The arch of the human foot is unique among hominins as it is compliant at ground contact but sufficiently stiff to enable push-off. These behaviours are partly facilitated by the ligamentous plantar fascia whose role is central to two mechanisms. The ideal windlass mechanism assumes that the plantar fascia has a nearly constant length to directly couple toe dorsiflexion with a change in arch shape. However, the plantar fascia also stretches and then shortens throughout gait as the arch-spring stores and releases elastic energy. We aimed to understand how the extensible plantar fascia could behave as an ideal windlass when it has been shown to strain throughout gait, potentially compromising the one-to-one coupling between toe arc length and arch length. We measured foot bone motion and plantar fascia elongation using high-speed X-ray during running. We discovered that toe plantarflexion delays plantar fascia stretching at foot strike, which probably modifies the distribution of the load through other arch tissues. Through a pure windlass effect in propulsion, a quasi-isometric plantar fascia's shortening is delayed to later in stance. The plantar fascia then shortens concurrently to the windlass mechanism, likely enhancing arch recoil at push-off
     
  2. scotfoot

    scotfoot Well-Known Member

    It seems to me that the authors of Welte et al 2021 have an idea that toe dorsiflexion prior to initial contact is important ,but ,because they have studied habitually shod feet and not habitually unshod feet , they have the mechanism of stress mitigation and its effects completely wrong .
     
  3. scotfoot

    scotfoot Well-Known Member

    LINK TO VIDEO src="https://youtube.com/embed/iZER9QtCKGM?start=69…
    Check out this 5 sec clip of the foot of an Olympic champion through initial contact , and see if you think the spring ligament comes under strain before the plantar fascia .
    Note ;the runner used to train barefoot .
     
  4. scotfoot

    scotfoot Well-Known Member

    So Welte et al 2021 has set the scene for potentially show stopping research ,hopefully in the near future . But first of all a time line .

    2009 Caravaggi et al look at toe dorsiflexion prior to initial contact and find that there was a lengthening of the plantar fascia at initial contact . They suggest that this pretensioning reduces crimping in the fascial tissues and better prepares the fascia to take load during initial contact .

    2015 Welte and Rainbow publish a conference abstract which includes the following -

    " ....there is less elongation during the initial contact phase of stance suggesting that the windlass may act as a protective mechanism for the plantar fascia during loading "

    So still nothing about the initial windlass protect the tissues of the foot in general from rapid transient loading .

    Feb 2018
    A thread is started by me on Pod Arena ,which I believe amounts to as a " grounded theory " . In short the theory suggests that the plantar fascia is wound around the MTFJ prior to initial contact and that it is "paid out " under tension during weight acceptance , helping to reduce rapid stress/ strain in the tissues of the foot .
    So like the arrestor wire of an aircraft carrier stopping a rapidly moving plane .

    August 2018
    The idea of the " initial windlass phase" reducing rapid tissue loading in the foot generally , finds its way into an experimental paper by Welte and Rainbow which is actual about toe off . Just seems to have dropped in from nowhere since the suggesting from 2015 was simply about rapid toe plantarflexion during initial contact protecting the PF ( With regard to the PF at toe off , Welte 2018 is a novel ,excellent paper ) .

    Now Welte 2021 "The extensibility of the plantar fascia influences the windlass mechanism during running "

    Drawing on experimental data and with regard to the windlass mechanism during initial contact , Dr's Welte and Rainbow have gone back to their original concept from 2015 ,and that is that during weight acceptance the pre strike dorsiflexed toes rapidly plantarflex protecting the plantar fascia from stress/strain and seeing the more proximal tissues ,such as the plantar ligaments , load preferentially .

    This is completely contrary to my grounded theory from 2018 and would tend to disprove it if it were not for the fact that the data collected by Welte et al was from habitually shod individuals .

    Going back to the analogy of the arrestor wire on an aircraft carrier .

    Imagine a plane coming down to land on said carrier . There are now two ways it can be stopped from sliding off the far end of the ship , 1 the arrestor wire ( representing the plantar fascia ) with resistance in the drums around which it is wound and 2 beyond that, a wall of steel ( representing the plantar ligaments )

    In the mechanism Welte and Rainbow have revert to in the 2021 paper , the arrestor wire unravels with no resistance from the drums around which it is wound absorbing no kenetic energy from the plane. Instead the plane ploughs straight into the wall of steel producing a crash .

    Surely the mechanism proposed in 2015 and then 2021 is no mechanism at all . That is to say if the toes rapidly plantar flex during weight acceptance with little or no resistance from the toe extensors ,why have them dorsiflexed prior to initial contact at all ?

    I believe that it is entirely possible that the research group involved in Welte 2021 has picked the wrong group to study since although the windlass mechanism during toe off is not affected by footwear the initial windlass phase must be .
    If this group were to conduct a study into the windlass mechanism in a habitually unshod population ,and then find that my theory was correct ,then they really would have something newsworthy .

    Presently they would appear to have largely disproved my theory since toes which rapidly plantarflex during initial loading , with no resistance from the toe extensors ,is not what I described at all .

    Its really worth going back to this video of the foot of a barefoot trained athlete , accepting weight . The video is super slow motion .
    LINK TO VIDEO src="https://youtube.com/embed/iZER9QtCKGM?start=69…
     
    Last edited: Mar 4, 2021
  5. scotfoot

    scotfoot Well-Known Member

    Regarding my theory from Podiatry Arena Feb /March 2018 here is a quote which relates to the initial windlass phase

    - " .If you like , it prevents a rapid "tension transient" in the fascia during weight acceptance and ameliorates the potentially damaging effects of high levels of kinetic energy in the tissues of the foot as a whole ."

    Welte et al 2021 ,a study carried out on the habitually shod ,would seem to indicate that their is very little " amelioration " going on . The initial windlass phase looks like a dead duck in the individuals tested , a non functioning mechanism .

    I am not sure why the researchers chose to do this research on the habitually shod ,but it gives some very valuable information . It demonstrates that the initial windlass is more or less non existent in shod populations .

    Now I could be completely wrong about " and ameliorates the potentially damaging effects of high levels of kinetic energy in the tissues of the foot as a whole " but the habitually barefoot now need to be tested .
    It could be that the foot behaves very differently during initial contact when hab shod/unshod are compared and that really would be some find .
     
  6. scotfoot

    scotfoot Well-Known Member

    With regard to the initial windlass phase of gait, I wonder if one of the benefits of dorsiflexion of the toes prior to foot strike might be connected with increased stroke volume during weight bearing . (It is important to note that the stroke volume of the heart is 70ml and the stroke volume of the plantar venous plexus of the foot alone, is 20-30ml with every step .)

    I introduced the idea that the whole foot is a gravity driven blood pump elsewhere on podiatry arena ,and by that I mean that during weight acceptance ,changes in skeletal foot shape are resisted by the fascias of the foot in concert with compression/distortion of the other tissues of the foot, particularly the intrinsic foot muscle mass . (see link to video )

    If, prior to foot strike, the toes dorsiflex, giving rise to closer approximation of the heel and forefoot and creating more volume between the plantar fascia and the bony arch of the foot, then this might make it easier for the vessels of the superficial and deep venous systems to fill with blood giving an eventual increased stroke volume .

     
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