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The plantar fascia and pressure under the toes

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Feb 27, 2022.

  1. scotfoot

    scotfoot Well-Known Member


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    I have read that tension in the plantar fascia translates into downward pressure from the digits onto the ground and I also believe that the plantar fascia helps support the medial longitudinal arch of the foot .
    However, what if their is no ground under the toes but the toes overhang a small drop ? Does that mean that the plantar fascia can offer less support for the medial arch ?
     
  2. Craig Payne

    Craig Payne Moderator

    Articles:
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    Yes.
    You can see that if you stand on an edge of something with the toes hanging over the end; the toes plantarflex below the horizontal surface
     
  3. scotfoot

    scotfoot Well-Known Member

    So if an individual is wearing shoes with a toe spring and the area under the toes yields and bends downwards under pressure, can that affect tension in the plantar fascia and so pronation .
     
  4. DaVinci

    DaVinci Well-Known Member

    The reverse windlass in action
     
  5. Craig Payne

    Craig Payne Moderator

    Articles:
    8
    Most likely, yes.
     
  6. efuller

    efuller MVP

    It depends on forces not position. When the toe applies force to the shoe, to bend it, and keep it bent, there will be tension in the fascia (and/or a tendon). You can say the force will probably change. It would be an interesting study to find out how much.
     
  7. scotfoot

    scotfoot Well-Known Member

    Moving proximal to distal the medial aspect of the plantar fascia can be said to attach at the heel then pass forwards and attach to the base of the hallux via the plantar plate .

    Leaving aside the extensibility of the PF, when an unshod foot accepts weight the PF, of length x cm, comes under tension and helps support the arch and resist pronation .

    In a shoe with a pliable toe spring, the pressure under the hallux will depress the toe spring as the toes plantarflex below the horizontal . This plantar flexion will bring the points of attachment of the PF closer together meaning that the medial longitudinal arch must flatten further before a given tension is reaching in the PF .

    If the points of attachment of the PF move 2mm closer together, will that affect pronation extent and timing ? Worth looking at perhaps .
     
  8. But the toe spring of the shoe will potentially dorsiflex the toes and not sure how the toes can “plantarflex beyond the horizontal” unless the foot is facing downward on an incline plane?
     
  9. scotfoot

    scotfoot Well-Known Member

    Shoe design is something you will know far more about than I do but I was basing my comments around a shoe that holds the foot and toes on the same horizontal plane, parallel with the ground .

    In light of Welte et al ,where the researchers found that the toes rapidly plantar flex during weight acceptance, loading the plantar ligaments in preference to the PF, toe springs that holds the toes in a plantarflexed position could be problematic .
    Some shoes, particularly those with a large heel drop and an inner design that slants to toes upwards ,might not allow rapid plantarflexion of the toes leading to abnormally high levels of loading in the plantar fascia and less than normal in the plantar ligaments .
    Could this set of circumstances trigger plantar heel pain?
     
  10. efuller

    efuller MVP

    I agree with most of what you say with the exception of ... bringing the attachments closer together.... The arch flattening is what creates the plantar flexion moment on the toe to bend the shoe. If we assume minimal change in length of the plantar fascia with tension, the distance between the attachments will be the same.
     
  11. I don’t think you mean “plantarflexed position”, IF the toe spring holds the toes in any position it would be dorsiflexed, right?

    We also need to be cautious and accurate with terminology here: toes may “rapidly plantarflex” from a dorsiflexed position but that does not necessarily mean they are plantarflexed at the end of that motion.
     
  12. scotfoot

    scotfoot Well-Known Member

    Whoops , correct .

    I am now pondering two different situations in the thread both of which involve toe springs and the plantar fascia .
    One in which the toes and proximal part of the foot start of on the same horizontal plane and then the toes compress the toe spring during weight acceptance thus becoming plantar flexed, and another in which the toes are held in a dorsiflexed position during weight acceptance and are prevented from moving onto the same horizontal plane as the rest of the foot by the rigidity of the toe spring .

    Some running shoes hold the toes in a markedly dorsiflexed position and have a construction that looks like it would hold them there during loading at weight acceptance. If the toes are stuck in a dorsiflexed position then the PF might be subject to excessive loading.

    So depending on construction, toe springs might promote excessive pronation by allowing toe plantar flexion beyond the horizontal or hold the toes in a dorsiflexed position causing excessive loading of the PF .
     
  13. efuller

    efuller MVP

  14. Do they though? We have to differentiate toe-spring on the mid/ outer sole versus toe spring on the last, the latter defines the shape of the foot-shoe interface. Also as I stand here in my Hoka Bondi’s I can freely both plantarflex and dorsiflex my toes; a bit like how the foot can move on top of a foot orthoses and is not “held” nor “braced” by it, the shoes do not prevent movement in my toes. Worth noting too that heel pitch increases the dorsiflexion position in the toes; while modern shoes have adopted rocker geometry, generally speaking the heel height differentials have decreased. Moreover, rocker geometry footwear is very helpful in treating patients with disorders of the windlass mechanism.
     
  15. scotfoot

    scotfoot Well-Known Member

    From pictures seen on the internet some modern running shoes, when cut away longitudinally, do seem to hold the toes in a dorsiflexed position.

    Agreed .

    Without altering the pressure under the ball of the foot ?

    Agreed .

    It might be a good idea to use a cluffy wedge in some circumstances but surely not all .
     
  16. dynamic is what we are talking here though, right? I’d want to see dynamic imagery.

    “Without altering the pressure under the ball of the foot ?”
    Pressure is dynamic: step to step variation, footwear variation, surface variation: viva variation!!!!
     
  17. efuller

    efuller MVP

    I think it may have been said before. It depends on the rigidity of the shoe. I've seen shoes when sitting on the floor the tip of the shoe is some distance from the floor and when the person is standing in them the tip of the shoe is on the ground. In other shoes the tip is still in the air.


    I think that was the consensus of that thread.
     
  18. scotfoot

    scotfoot Well-Known Member

    Would static balance be more of a challenge with the tip in the air ? I think it would be .
     
  19. scotfoot

    scotfoot Well-Known Member

    The various manufacturers will know .

    I believe shoes take work away from the toes during toe off esp if the shoes have a stiff sole .
     
  20. efuller

    efuller MVP

    Possibly, possibly not. It would depend on the excursion of center of pressure during balance. When the center of pressure under the foot is distal to the most anterior point of contact of the outer sole, a force couple will be created (downward force from the foot applied to the shoe and upward force from the ground applied to the shoe.) and the shoe will rotate. That would make balance more of a challenge.

    With a rocker that lifts off of the ground just proximal to the metatarsal heads: To get the center of pressure anterior to this point, there would have to be almost no weight on the heel. In most situations the excursion of the center of pressure is not this not this much. For most people, the rocker tip won't cause balance problems. For those with balance problems, with larger excursions of the center of pressure, rocker tip shoes would be more unstable.
     
  21. efuller

    efuller MVP

    I would word that a little differently. The person could choose not to work the toes in a stiff soled shoe. The person can still contract toe muscles in a stiff shoe and that would still do work. (Work has a specific meaning in mechanics and it might not be the right term we are looking for here. I don't feel like thinking that hard right now.)
     
  22. Indeed, I think it was Nigg’s group that showed that dorsiflexion of the toes during gait is associated with power absorption and thus negative work.
     
  23. scotfoot

    scotfoot Well-Known Member

    In the unshod condition the toes press down and prevent unwanted rotation about the ball of the foot during gait . The PF provides some of this pressure and the toe flexors the rest. A stiff soled shoe will add to the downward pressure once it is bent upwards ( it wants to spring back ) and may have a grip component/contour to further assist with traction in the sense of grip.


    The body is very good at feedback and I believe it entirely plausible that over time the toe flexors could simple put in less effort since less is required .

    Moving from a normal shoe to a minimal shoe saw toe flexor strength increase by 57% in one recent study and I think this has little to do with cushioning or medial arch support and much more to do with toe springs and, most particularly, sole/shoe/foot passive stiffness once the system is dorsiflexed.

    Yes, negative work at the level of the foot but positive work in a systemwide sense since pushing the toes down prevents wasteful rotation of the entire body during gait.
     
    Last edited: Mar 10, 2022
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