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Windlass mechanism not main stiffener of the foot at push off !

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Jul 19, 2020.

  1. scotfoot

    scotfoot Well-Known Member

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    So another very interesting paper from Farris and Kelly (see link below ) .

    This paper lays out a case that the windlass mechanism is not the primary stiffener of the foot during push off , but rather that this stiffening is provided by muscular forces including a major contribution from the intrinsic foot muscles . The authors argue that this contribution helps limit strain in the plantar fascia and that strengthening of the intrinsics may help treat, or prevent ,plantar fasciitis .

    Foot stiffening during the push-off phase of human walking is ...

    royalsocietypublishing.org › doi › rsif.2020.0208
    4 days ago - Several plantar intrinsic foot muscles course a parallel path to the plantar aponeurosis from the heel to the toes (figure 1). These muscles are active during the late stance phase of gait [14,15] and appear to be important for modulating foot mechanics [16–19].
  2. scotfoot

    scotfoot Well-Known Member

    Here are some quotes from the Farris /Birch/Kelly paper .

    "Also, that the plantar intrinsic muscles can offload plantar aponeurosis strain might be of interest to clinicians and athletic trainers who seek to rehabilitate or prevent plantar fasciitis. This is a common syndrome resulting from repeated loading of the plantar structures in the foot [23]. Our findings suggest that strengthening of the plantar intrinsic muscles has the potential to shield passive structures from larger strains that could be contributing to this condition."


    "In summary, our results show that maintaining tension across the plantar aspect of the foot involves active muscular contraction of ankle plantar flexors and plantar intrinsic muscles. Therefore, the passive windlass mechanism is not the foot's source of rigidity for push-off against the ground during gait. In fact, within the foot, increasing push-off for changes in gait mechanics relies primarily on foot muscles and not winding of the plantar aponeurosis via the windlass mechanism."
  3. scotfoot

    scotfoot Well-Known Member

    In general the work of Kelly ,Farris and their numerous coworkers is to be applauded since they are improving understanding of the physiology and mechanics of the foot which may lead to better treatments and/ or performance .

    However , in this latest paper Farris et al have not touched on the transverse arch of the foot and the changes that take place in this during transition from mid to late stance . I feel pretty sure that the metatarsal parabola will give rise to very significant changes in foot stiffness around push off time .

    You could do worse than have a look at the video linked to below . In this simple 10 second clip the hand is used as an analogy for the foot with the knuckles representing the tarsal ( formed into a bit of an arch shape by the elastic band) ,
    and the fingers the metatarsals .
    See how the relationship of the finger tips ( met heads )changes as the hand lifted .
    Note that this effect is quite different from Vankandesen's fish fin mechanism

  4. kevin miller

    kevin miller Active Member

    Good luck to them, I hope people listen. What he is describing is biotensegrity, a view that some of us have been talking about for years, only to be shot down at every turn. That said, there is more to this than intrinsic musculature. The extrinsic muscles. 1) p tib, p longus, p brevis, abductor hallucis, and the great toe flexors provide transverse arch control and a direct transfer of force proximal in the kinetic chain on loading. 2) The peripheral nervous system.....those mechanoreceptors that constantly monitor and manipulate tension synergies.....are vastly underappreciated. 3) Related to muscle synergies is conversion of concentric action to eccentric for repetitive motion such as gait, pitching a baseball, and typing to name a few. The world of biomechanics is a bit resistant to change........
    Cheers, K
  5. scotfoot

    scotfoot Well-Known Member

    Some aspects of biomechanics are indeed resistant to change no matter what the evidence says .
    My own pet peeve is the use of the towel curl exercise to strengthen the intrinsics .

    This exercise or associated exercises which employ apparatus that provide resistance to toe curling via toe bars etc , just don't target the intrinsics sufficiently for strength gain no matter the level of effort .Dr Sarah Ridge and her colleagues recently demonstrated this using a custom built rig and indwelling electrodes .And yet some researches, particularly it the Far East , persist in measuring toe flexor strength with toe grip dynamometers which can't meaningfully pick up the majority of intrinsic flexor strength .
    Often wasted research time if you ask me and frustrating to see .
  6. scotfoot

    scotfoot Well-Known Member

    On the subject of progressive resistance training and the muscles of the foot , a paper was published a few years ago which looked at the effects of this type of exercise as a treatment for Charcot-Marie -Tooth disease . The study , led by Professor Joshua Burns concluded as follows ;

    6 months of targeted progressive resistance exercise attenuated long-term progression of dorsiflexion weakness without detrimental effect on muscle morphology or other signs of overwork weakness in paediatric patients with Charcot-Marie-Tooth disease."

    Here is a link to an article on the subject ;

    First effective treatment of children with Charcot-Marie-Tooth ...

    www.sydney.edu.au › news › 2017/07/17 › first-effecti...
    17 Jul 2017 - Led by Professor Joshua Burns from University of Sydney and The Children's Hospital at Westmead, the study found that progressive resistance exercise could help to significantly reduce the muscle weakness experienced by patients with the genetic disease.

    Forward to the present day and Professor Burns is moving to improve methods of strengthening the intrinsic muscles of the foot . He is basing his method around the short foot exercise but has correctly identified that,during exercise , the toes should remain straight but flex around the MTFJs causing pressure to be applied to the ground through the tips of the toes and the ball of the foot to leave the ground ( see link to photographs from the paper and to the paper itself ) . He and his team are calling their system the "Archercise biofeedback device ".


    Feasibility of the Archercise biofeedback device to strengthen ...

    jfootankleres.biomedcentral.com › articles
    13 Jul 2020 - Toe flexor and foot arch exercises focused on intrinsic foot muscle strength and ... We investigated the feasibility of using a novel medical device, known as ... J. McKay, Claire E. Hiller, Elizabeth J. Nightingale & Joshua Burns.
    by PJ Latey - ‎2020
  7. kevin miller

    kevin miller Active Member

  8. kevin miller

    kevin miller Active Member

    LOL... Agree with you RE the towel exercises. Not all that functional. My favorite ther-ex for cases that require significant rehab is walking backwards in sand. It is cheaper for the pt to build a shallow frame and fill it with sand that go to weeks of PT.
  9. scotfoot

    scotfoot Well-Known Member

    I have come across a few instances of foot health care professionals doing rehab with professional athletes in sandpits and the like .

    Re the towel exercise I feel that the evidence teaches that this is not only not a functional exercise but also that it only exercises the intrinsics ( QP apart ) as ancillary muscles .

    So, for example, if an individual places their toes over a bar of a custom made dynamometer and pulls back on the bar with all the might their toes can muster,the quadratus plantae and the long toe flexors will contract to near the max force they can apply but the intrinsic muscles, except QP , will become activated to nowhere near their maximum levels .

    So toe curls will strengthen the long toe flexors but will never strengthen the intrinsics no matter how hard a subject tries .

    It might help to think of the bicep curl .This exercise is good for building bicep strength but during its execution some muscles in the back activate and act as ancillaries to stabilise the shoulder . So the bicep curl activates some muscles in the back but not sufficiently to effectively strengthen them . And so it is with the intrinsics and toe toe curls

    This is probably not a big problem if simple towel curls are being used as an exercise but could well introduce muscle imbalances if toe curls are done with a progressively increasing resistance level. The extrinsic may end up overpowering weak intrinsics detrimentally affecting function .
  10. kevin miller

    kevin miller Active Member

    Here is something for you to noodle on.....
    When I was working on my masters and doctorate, I worked in the gross lab and for three years was able to dissect anything I wanted...and do experiments. I think that the extrinsic moves are more important than given credit. Primarily, post tib, ant tib, peroneus long, pro brev, flex hallux abductor hallux. Their combined action, just before the foot begins to load, is to shorten and narrow the foot. For instance post tib and P longus make a sling under the navicular and cuboid. Post tib doesnt stop at the navucular, it continues through the foot and sends tendons to the lateral tarsal and sometimes to the base of the 4th and 5th mets. P longus inserts on the base of the first. So when they shorten, they tilt the rearfoot up......at the same time, abductor H and P brevis shorten the foot.....in otherwosrds, the make the midfoot joints congruent. When the foot loads, those muscles act eccentrically to maintain foot position, but more importantly to store and transfer energy from loading up the leg and to trigger muscle synergies needed for gait via mechanorecptors. BUT! What keeps the mets from simply flattening out? The attachments of the muscles mentioned are all proximal to the mets? Enter the intrinsics......

    All the towel exercises in the world won't produce that action.....but walking backward is the same functional position as sprinting......an action where all the foot muscles have to fire together to maintain structural stability.

    Sorry about the brevity, errors and lack of detail....typing this on my phone.
  11. scotfoot

    scotfoot Well-Known Member

    I largely agree with what you are saying about the extrinsic foot muscles and the support they provide for the structure of the foot and indeed some manifestations of the short foot exercise ,where the toes don't push against the ground , are almost entirely about these muscles and not the intrinsics at all .

    Going back to that pet peeve of mine ,the toe curl exercise and its variants , a couple of papers have measured the activity levels of the abductor hallucis during this exercise and the results point towards this muscle being ancillary to the flexor digitorum longus which contributes by far the most force during the exercise .

    For anyone who might not be familiar with the term , "EMG max "refers to the electrical activity in a muscle during its maximum voluntary contraction . Researchers sometimes record this figure then express subsequent effort levels in the muscle as a percentage of this figure . So if the studied muscle is worked at half the level of its voluntary maximum you might expect to see an EMG figure of about half the EMG max figure .

    So back to those papers .
    The first is Jung et all 2011 (see link below ). These researchers found that the EMG level in the abductor hallucis ,during a standing toe curl exercise ,was 17.5 % max. That is a low figure and demonstrates that the abd hallucis is not a major player in this movement but is ancillary . At 17.5 % max you will be there for a very long time doing a huge number of repetitions to get a strengthening effect , if you ever get one at all .

    A more recent paper is that of Bruening et all 2019 ( Link also below ) . For this research the investigators built just about the best possible toe curl measurement device possible ,indeed its doubtful if the abductor hallucis could have been involved anymore than it was in the curling action . However, even with the test subjects pulling on the ring ( curling their big toe back towards the heel ) with all their might ,the EMG figure did not get much above 30 % EMG max for the abd hallucis . So with a following wind and the best possible set up ,toe curls will strengthen the flexor hallucis longus but not the abd hallucis ,or at least not effectively .
    Actually that EMG max figure used by Bruening et al was arrived at by recording the EMG in abd hallucis during a single leg calf raise with support and as such is liable to be much lower than the true EMG max . The 30 % figure for the toe curl exercise is probably a good bit higher than it should be .

    As far as I am aware these two papers are the only ones to measure the activity in the abd hallucis during toe curl activies and as you can see it is a very poor choice for strengthening this muscle ( and probably ,QP aside and in my opinion , a poor choice for strengthening the other intrinsics as well )

    Jung DY, Kim MH, Koh EK, Kwon OY, Cynn HS, Lee WH. (2011) A comparison in the muscle activity of the abductor hallucis and the medial longitudinal arch angle during toe curl and short foot exercises. Physical Therapy in Sport 12;30-35

    Bruening et all
  12. scotfoot

    scotfoot Well-Known Member

    Going back to the original post in this thread and the paper by Farris et al ,I have to say that this paper appears not to have gone down well among some well regarded and influential individuals .

    In discussing this very interesting piece of search further it may be a good idea to look first at Welte et al 2018 . They used the rig shown below to study the windlass mechanism where the plantar fascia wraps around the MTPJs which in turn raises the medial arch of the foot and more closely approximate the met heads with the heel (Hick ).
    The authors thought this would stiffen the foot but the opposite turn out to be the case .

    So looking at the diagram , Welte and colleagues increased the MTPJ angle to engage the windlass . They found that for the same applied force down through the tib/fib the bit on wheels ,well ball bearings , moved more when the windlass was engaged (MTPJ ANGLE ) . Or in other words ,engagement of the windlass produced increased tension in the plantar fascia but reduced foot stiffness ; so increased PF tension does not necessarily equate to increased foot stiffness in vivo .

    Here is how it was explained in the paper .
    "The windlass did, however, modulate the energetics of the arch during dynamic loading. When the windlass mechanism was engaged, the arch was shortened significantly, which probably placed other tissues crossing the arch closer to their resting length. The arch could therefore go through a greater excursion due to the nonlinear elastic properties of the arch-spanning tissues. This would functionally reduce the bulk stiffness of the arch and lead to greater elongation, and consequently facilitate greater energy absorption and dissipation during cyclic loading of the foot. While the effect of perturbing the MTPJ angle on the specific internal structures of the foot cannot be determined with these methods, it is possible that modification to the shape and length of the arch changed the proportion of the load delivered to the arch's soft tissue structures. Differences in viscosity between these structures could also influence the dissipated energy in the arch."

  13. scotfoot

    scotfoot Well-Known Member

    With regard to the very recent Farris ,Birch ,Kelly paper ( link below ) I would have to say that I have issues with some of the interpretation , most particularly with the assertion that the windlass is not engaged until the tension in the PF and achilles tendon is decreasing .

    However ,this is the first paper to factor in the intrinsic foot muscles when considering tension within the PF during gait and as such is a very important step forwards. It highlights the importance of the intrinsic foot muscles both with regard to the forces around the MTFJs and draws attention to the protective function that the intrinsics seem to have over the plantar fascia .

    How accurate can previous models be ( finite element / cadaver based experiments ) if they have left the intrinsics out of the equation ?

    If the intrinsics have a protective role to play when it comes to strain within the plantar fascia then it is very likely the extrinsic toe flexors are also involved .Strengthening of these muscles may be key to treating/ preventing plantar fasciitis .It is known that the plantar flexors respond quickly and to a high degree to approprate exercise regimes ,and using the right apparatus 3x 10 mins a week is enough to promote strength gains even in intrinsic minus feet with neuropathy .

    Ps I have no idea if Luke Kelly reads the material I post here but with regard the the "initial windlass phase " as I am calling it , friends and family involved in research tell me they would never reference a blog site in papers for publication ,and so ,if that is the way things are done , no harm no foul . :)
    Last edited: Aug 2, 2020

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