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The myth of toes curling to grip the ground

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Apr 28, 2022.

  1. efuller

    efuller MVP





    Model of Flexor digitorum brevis. Non weight bearing (tendon up) pull of the tednon causes flexion of mpj and PIPJ
    Weight bearing (Tendon down) pull of the tendon causes dorsiflexion of MPJ and plantar flexion of PIPJ.
    There is an anomaly with this model in that when the PIPJ plantar flexion it effectively shortens the toe and the proximal movement of the head of intermediate phalanx causes a proximal to distal push from the surface on the eye screw in the distal phalanx which causes the distal phalanx to dorsiflex. This probably would not happen if this was done on a smooth surface and the eye screw could slide. Then the model would look like the picture that we were discussing earlier.

    Yes, when I held the model up in the air and did not put the tendon through the eye screw proximal to the MPJ and pulled at an angle similar to Gerry's video, I got the same results he did.
     
    Last edited: Oct 3, 2022
  2. scotfoot

    scotfoot Well-Known Member

    Thanks for putting the video up.

    In your model you have the pull of the tendon parallel to the long axis of the proximal phalanx. During its path along the proximal phalanx (PP) ,going from distal to proximal ,the tendon of the FDB is held in close approximation to the plantar surface of the bone by a synovial sheath. As the proximal phalanx approaches the head of the metatarsal it is enveloped in a joint capsule which includes the plantar plate. The FDB tendon does not pass through the capsule but under it, so must depart the plantar surface of the PP at an angle somewhere close to the joint capsule . This would give a downward pull on the PP not represented in your model.
    In my model I have tried to factor this in, the hence the angle of pull.

    ( Just had another look at your video and the 2 "toes" are not rigged the same way . One has a ring close to the proximal end of the PP through which the cord ( FDB tendon) passes but the one you are using in the video does not . I suspect it's an old model and the ring has simply been lost over time.
     
    Last edited: Oct 3, 2022
  3. efuller

    efuller MVP

    I agree with you up to the point where you say there is a down ward pull on the phalanx. When the tendon is close to the joint capsule, this means that you can't get downward pull. The tendon has to be down to create a downward pull. In addition, body weight holds the metatarsal head on the ground and the body weight would resist plantar flexion of the MPJ (plantar flexion of the MPJ would lift the metatarsal head off of the ground).
     
  4. scotfoot

    scotfoot Well-Known Member

    I'm not sure what you mean by this . If you look at the model you have made of a lesser toe nearest to the camera in your plantar side up introduction, you can see the cord go through the metal loop on the distal end of the member representing the proximal phalanx then angle up towards the loop on the metatarsal . Upwards force or downward once you flip the model upside down/right way up .

    Yes, body weight holds the met head down and the toe flexors ( intrinsic and extrinsic acting together ) pull the toes down towards the ground creating pressure under the toes, a key to unshod locomotion. If the intrinsics are very weak the toes buckle .

    Take toes which buckle under load ,strengthen them, and they no longer buckle . I have seen this many times over the last decade and first witnessed it in my own feet.
     
  5. efuller

    efuller MVP

    When a muscle shortens, it pulls the tendon towards its attachments to the bone. The muscle is pulling the tendon upward, not downward, as seen in your video. The pull of a tendon can be redirected by a pulley. The pulley, in this case, does not redirect the pull of the tendon far enough to justify the direction of pull in your video.

    In my video I did not use the "toe" with the loop at the base of the proximal phalanx. This allows the tendon to move farther from the joint. (more like in your video). If it went through the other loop, the tendon would have an even smaller lever arm at the MPJ and be even less likely to cause plantar flexion of the MPJ.

    My model clearly shoes how contraction of only FDB causes toes to buckle like it does in the picture.

    Show us a picture of someone pressing their toes into the ground and the toes staying straight. Then we might be able to explain your observation strengthening the muscles keeps the toes straight.
     
  6. scotfoot

    scotfoot Well-Known Member

    I will look out a video clip and put it on youtube.

    QUOTE="efuller, post: 414778, member: 864"]My model clearly shoes how contraction of only FDB causes toes to buckle like it does in the picture[/QUOTE]

    With the toes under load, the proximal ring will act as a point of attachment and influence proximal phalanx movement in a way not represented in your video . Or put another way the most proximal metal loop of the model in your video acts like a sling as would the synovial sheath .

    Could you show a pull on the cord (FDB contraction) with the the cord passing through the most proximal ring and then around a joint capsule at the head of the " metatarsal "( a sphere of some sort; rubber impression material etc. )

    I feel that of the two toe models in your video the one you have used has no proximal ring /synoveal sheath/sling , representation, and is therefore flawed .

    You do not seem to be willing to reference the synovial sheath.
     
  7. efuller

    efuller MVP

    Gerry, why do I need to reference the synovial sheath if the rings are in the model? Passing the tendon through another ring actually lowers the lever arm of the tendon to cause plantar flexion.

    You have already stated that the tendon is close to the metatarsal head. The eye screw in my model probably places the tendon farther from the joint, proportionally, than the tendon is from the metatarsal in reality. How big do you think the joint capsule is? How much farther from the metatarsal do you think the tendon should be in my model?
     
  8. scotfoot

    scotfoot Well-Known Member

    Here is my foot under load . I strengthen my feet every other day . The toes remain straight during unsupported balance on the ball and toes of one foot .
     
  9. scotfoot

    scotfoot Well-Known Member

    You could rig your model so that the FDB exerts a similar force on the proximal phalanx as the plantar fascia does. I am assuming you accept that the plantar fascia exerts a plantarflexing moment on the proximal phalanx of the lesser toes ?
     
  10. efuller

    efuller MVP

    But the FDB doesn't exert a plantarflexion moment on the proximal phalanx like the plantar fascia does. We are trying to explain the effects of muscle strengthening.

    You are still neglecting body weight and ground reaction force at the metatarsal head. If the tiny little FDB, or the massively strengthened FDB, is not strong enough to lift the metatarsal heads off of the ground the MPJ will not plantarflex.

    My model clearly shows that FDB tendon tension can create the toe "collapse" seen in the picture. Do you have another explanation of toe collapse? What are the forces and moments that create that shape of the toes?
     
  11. scotfoot

    scotfoot Well-Known Member

    Oh , and why not ?

    Thanks to the synovial sheath, acting as a sling , it (FDB) effectively has an attachment close to the point of attachment of the facia.

    I am saying the FDB pulls the proximal phalanx down to the ground and prevents toe collapse during loading of the forefoot . You can have force without movement .

    Your model is clearly deficient for the reasons outlined above.
     
  12. efuller

    efuller MVP

    The difference is the tendon slides through the sheath as opposed to attaching directly to the bone. It's like tying the tendon to the ring instead of just passing the tendon through the ring. It applies force differently to the ring.


    You did not respond to my criticism of your critique. Why do you thing the eye screw should be farther from the metatarsal than it is.
    If I put the tendon through the ring on the base of the proximal phalanx and got the same motion, would you agree that the model is valid.

    You still have to come up with an alternate explanation of why the toes do buckle. The model did show buckling just like the picture.
     
  13. scotfoot

    scotfoot Well-Known Member

    I don't think it is materially different . The tendon is effectively attached at the ring .

    You don't have an eye screw acting as an effective sling on your model at all, at least not the one you used in the video

    If you used your "alternative toe" and put the tendon through the ring at the base of the proximal phalanx you would be making a move in the right direction.
    However, you should be looking to apply force in much the same way as the flexor hallucis brevis does to the proximal phalanx of the big toe . The angle at which the tendon leaves the surface of the proximal phalanx and travels over the joint capsule matters . That's why we have the sesamoids associated with the hallux.

    The lesser toes buckle because of weakness in the FDB muscle . Strengthen these and the toes don't buckle ( see video) .

    Eric ,under load my toes used to collapse just like in the picture . Once I strengthened them they no longer collapsed under load but remained straight . What is your explanation for this ?
     
    Last edited: Oct 6, 2022
  14. efuller

    efuller MVP

    Gerry are you claiming the tendon does not slide through the sling? It's a tendon sheath, it is supposed to be slippery to allow the tendon to slide. When the tendon is attached to ring, it does not slide. Through the ring, the tendon slides like it does in reality. They are functionally different.

    The eye screw on the "metatarsal" functions really close to having an eye screw on the base of the proximal phalanx. I'll post the video if you concede that is what the anatomy does in reality. You are welcome to explain why you think it works differently.

    Weakness does not cause motion. In the picture, the toes have moved into a "buckled position". What loads are causing the buckling and how does the strengthening prevent the buckling?

    One explanation of the video of your toes is that you are not actively contracting FDB. It may be stronger, but does not mean that you are using it.

    Another possible explanation is the lumbricals. The lumbricals can plantar flex the MPJ and dodrsiflex the IPJs through the extensor hood.

    I'd lean more toward the lack of contraction of the EDB in the video. In the picture with the "toe collapse" you can see the toes blanche from increased pressure. In the video of your toes you don't see blanching.
     
  15. scotfoot

    scotfoot Well-Known Member

    Excuse me Eric, but my model has a "synovial sheath" through which the tendon slides and yours doesn't .
    If you look at my model you can see I have the tendon leaving the surface of the proximal phalanx at about 30 degrees . If it were 90 degrees you could more readily appreciate that the tendon sheath would transmit load to the underlying bone at the point were the tendon leaves it . That force or load would be at 90 degrees much the same as would happen if the tendon were directly attached to the bone . In a static hold nothing is sliding.

    No ,all the evidence says the FDB is active in single leg stance and at heel off during gait

    You would appear here to be saying weak intrinsics can cause the toes to collapse into a hammer toe configuration and strengthening them can keep the toes straight, all be it that you are considering the lumbricals and not FDB. If that is the case the discussion is making some progress .

    No .The blanching has little to do with pressure and more to do with joint position . You can get the same effect from a finger .

    I don't know what you mean . I do realise that this discussion challenges views you have held for many years .
     
    Last edited: Oct 8, 2022
  16. efuller

    efuller MVP

    I see the 30 degrees, in your model, and you still have not justified that. If you look at a weight bearing x-ray and draw a line from a point just plantar to base of the phalanx to just plantar to the metatarsal head it is at most 10 degrees. A 30 degree line puts the tendon almost outside of the plantar skin. The pull of the tendon is nearly parallel to the phalanx, so the downward pull on the pulley is minimal.

    Why would two rings be different than a sheath? The rings apply a force at the location where a sheath would change the direction of the tendon. That makes the rings function the same.

    You are welcome to demonstrate your sheath at a more reasonable direction of pull in a "weightbearing" situation.


    Yes, but your picture is not during gait and you are choosing which muscles to contract to keep your toes straight.

    The muscles are are under CNS control and the CNS can chose to fire or not.


    That's funny. You are the one who has an economic interest in denying that FDB, when weight bearing, will cause the motions seen in the picture.

    Gerry, you dodged the question of what does cause the position of the toes seen in the picture. If you ask the person whose toes are in the same position as those in the picture, they will tell you they are contracting their foot muscles. The toes in that picture achieve that position because of muscle contracture, not because of muscle weakness.
     
  17. scotfoot

    scotfoot Well-Known Member

    "draw a line from a point just plantar to base of the phalanx to just plantar to the metatarsal head it is at most 10 degrees."

    The tendon of the FDB does not pass just plantar to the met head but has to pass around the joint capsule which includes the plantar plate, so a greater angle .

    You do not have two rings on proximal phalanx in the model you used for your demonstration .

    I believe my model is a better representation of the situation than yours but I still would not attempt to draw definitive conclusions from it, as you seem to be attempting to do from your model.

    My video is taken during single leg stance, through, up, into ball of foot stance with a heavy load on toes. Kelly has shown this activates FDB . People can't keep their toes straight in this position if the intrinsics are very weak. The toes collapse and there is nothing they can do about this.

    My muscles are under CNS control and if I attempt a single hand, hand stand I will collapse into a heap whether I want to or not.

    Don't see why its funny Eric , the comment relates to the difficulty we all have with changing our minds esp after holding a particular opinion for a long time . There are books on this .

    If you ask people to put pressure onto their toes ( under supervision) and don't tell them specifically why you want them to do this, you get the results I am claiming, that is straight toes with stronger feet and toe collapse with weaker feet . It is not volitional and in fact people find it quite hard to move their toes in specific ways.

    Again, conclusions drawn from our primitive models cannot be regarded as definitive.
     
    Last edited: Oct 11, 2022
  18. efuller

    efuller MVP

    When you look at a lateral x-ray the height of the proximal phalanx and the lesser metatarsal head are about the same off of the ground. The tendon does not attach to the base of the phalanx, but passess plantar to the phalanx and is held in place by the sling. So if you made the assumption that the capsule thickness is the same at both locations you would assume a straight line. I was being generous when I gave you 10 degrees of upward angle of the tendon. An assumption of a 30 degrees, like in your model, is not consistent with the anatomy. Your model also is non weight bearing. The point of making the model is to see if there is a difference when weight bearing. My model shows a difference when weight bearing.

    I would agree that, without training, most people are not able to control the individual muscles. However, with training people can separate the contracture of different muscles. If you want, I'll post a video of contraction of various muscles in my hand showing the effect of different muscles. The anatomy is similar. If you chose the right muscle you can make the same shape in your fingers as seen in the pictures of the toes. Contraction of a muscle caused the toe deformity seen in the picture.

    "It is really hard to get someone to understand something when their paycheck is dependent on them not understanding that thing."
    What specific long held belief of mine are you referring to.?

    When the predictions of a certain model with certain assumptions replicate reality and another model, with different assumptions does not, you should favor the one that replicates reality.

    Perhaps your muscle strengthening device strengthens the lumbricals which might then be strong enough to counter act the moments created by EDB. However, EDB, acting on its own, will create the position of the toes seen in the picture.
    j
     
  19. scotfoot

    scotfoot Well-Known Member

    Please show the radiograph you are referring to.

    Yes , with untrained individuals loading weak toes produces collapse and with stronger feet the toes won't collapse . I have no idea where your hand comes into this.

    The one we are discussing .

    Ok, mine since mine has a sling and yours does not .

    Eric, here is a question I have asked you a number of times before but one you have never answered. Indeed, it generally stops you contributing to a thread entirely. The question is : What exercises do you prescribe for your patients to strengthen their intrinsic foot muscles ?
     
  20. efuller

    efuller MVP

    I'll let you justify your 30 degree angle.


    I have better muscular control of my hand than my foot. With my hand and foot I can demonstrate that contraction of a muscle creates the "collapsed" toe position. The point is active contraction of the muscle creates the position of the toes/ fingers. The other point is that I can selectively activate the muscles to produce different positions of the toes. It supports the argument that the choice of what muscles you activate determines the motion that you see. It's not that a muscle is weak, it's that it is not activated. In my hand, I have the control to individually activate different muscles and not activate others. It takes time to learn how to differentiate the muscles in the foot.

    Gerry, you are still ignoring the question on what causes the toes to collapse. I want you to go deeper than just saying it is muscle weakness. Which muscle(s) is/are weak and how does strengthening a muscle, and which muscle is strengthened, change what you see. Do you believe that the toe collapse is caused by something other than a muscle contraction? What causes the motion from a straight toe position to the collapsed position. One of my long held beliefs is that if see motion, something caused it. Newton's 2nd law.

    You never answered the question about whether you would accept the results of a video with the tendon going through a ring on the base of the proximal phalanx. The other question you never answered was why this would be different than a complete sling. I not going to bother to do the video if you keep moving the goal posts. If you were curious, would





    The question is irrelevant to our discussion about what causes "toe collapse" (flexion of PIPJ and hyperextension of the DIPJ)

    When patients ask if there are some exercises they can do for their foot. I will test their strength. If their lumbricals are weak I will demonstrate a some muscle strengthening exercises. Gerry does your device isolate the lumbricals?
     
  21. scotfoot

    scotfoot Well-Known Member

    "Please show the radiograph you are referring to."
    Your reply "I'll let you justify your 30 degree angle." Or in other words "no, I won't show you the radiograph I have been referencing ". But why ?

    You said -
    "It supports the argument that the choice of what muscles you activate determines the motion that you see. It's not that a muscle is weak, it's that it is not activated."

    And yet that contradicts something you said only a couple of posts ago-
    "Perhaps your muscle strengthening device strengthens the lumbricals which might then be strong enough to counter act the moments created by EDB". So weakness in the lumbricals causing collapse.

    The toes will adopt the position of maximum mechanical advantage given what they have to work with . Strong FDL and weaker FDB will produce collapse as the toes are loaded .

    I don't rate your model Eric, sorry.


    Actually the thread has a lot of material about foot strengthening in it and also you keep bringing up my foot strengthening device. Given this I feel it's fair to ask you what specific foot strengthening exercises you use and it is really obvious when you won't answer . Given your profession and that your license presumably allows you to carry out physiotherapy on the foot, that is odd.

    So back to my device . No Eric it does not isolate the lumbricals, but as toe flexors it will strengthen them along with many other muscles . Moving the toes around the MTPJ whilst keeping the IP joints straight activates the FDB more than toe curls. Toe curls are more an exercise for the extrinsic toe muscles and will barely activate muscle like FHB or ABDH .

    I look forward to hearing what specific exercises you prescribe for your patients.
     
  22. efuller

    efuller MVP

    So you came up with 30 degrees of angle of pull without looking at an x-ray. You can google weight bearing lateral foot x-ray.

    If you are unwilling to explain your 30 degree assumption, I'll just have to a guess. At angles lower than that you see toe collapse?

    Looking at the anatomy, a 30 degree angle of pull is just a bad assumption.


    My statements are not contradictory. In the video of your foot we do not know if EDB is not activated or not. In the picture we do not know if the lumbricals are activated, or not. From modeling when the FDL tendon is pulled, you get the same collapse, but at the DIPJ.

    Gerry what are you talking about? You already have rated it. I was just asking you how to make it good enough so that you would accept it. Obviously, nothing would be good enough because you are afraid that it would show that contraction of the EDB creates "toe collapse" as the conditions in my video showed.

    Actually, my model is the exactly the same as yours. With your conditions it did the exact same thing your model did. I'm just saying that your conditions are not consistent with reality. For the tendon to have a 30 degree angle leaving the toe, the tendon would be outside of the foot. Look at the video of your model. Do you really think the tendon could be that far from the metatarsal head and still be within the foot? And weight bearing matters.
     
  23. scotfoot

    scotfoot Well-Known Member

    1st MTPJ but you get the idea .Is the MTPJ in your model even remotely like this ? Will get back to you on the rest .

    [​IMG]
     
  24. scotfoot

    scotfoot Well-Known Member

    The nature of the MTPJs of the lesser toes is material to the way they function . My model is just a pile of unrepresentative sticks and string and so is yours. Let's move on please .

    Experience has taught me that people who do a lot of hill walking or play a lot of sports have toes that remain straight under load and couch potatoes have feet which generally collapse under load . There is nothing volitional about this ,they make no conscious choices, it's just the way things are.

    Could this be explained in part by stronger lumbricals ? ; yes that is probably part of it .

    Could the collapse configuration of the toes under load be due to "switched off" FDB ; no because the opposite has been demonstrated to happen . Why make up explanations that blatantly disregard the evidence?
     
    Last edited: Oct 19, 2022
  25. efuller

    efuller MVP

    Those three small arrows are in the bone. That attachment to the bone is at the bottom most arrow. If you draw a line from the bottom most arrow toward the proximal attachment of the muscle you see a line of action of the force that would pull upward, not downward, as in your video. Thanks for proving my point.
     
  26. efuller

    efuller MVP

    Models are useful when they reproduce reality. The modeling of EDB in my video reproduced the motion and position of the toes seen in the picture of the collapsed toes. Your explanation of that toe position is that it is caused by muscle weakness. Weak muscles don't move joints. Joints moved to cause the "collapse." My position is that the toe collapse is caused by EDB strength and contraction.

    Gerry, is that what you intended to write? It is backward to what I am saying.
    The collapse is caused by the switched on EDB and the lack of collapse happens with a switched off EDB. Yes, let's stop ignoring the evidence and move on.
     
  27. scotfoot

    scotfoot Well-Known Member

    1st MTPJ but you get the idea .Is the MTPJ in your model even remotely like this ? Will get back to you on the rest .

    [​IMG]
    Click to expand...​
    "Those three small arrows are in the bone. That attachment to the bone is at the bottom most arrow. If you draw a line from the bottom most arrow toward the proximal attachment of the muscle you see a line of action of the force that would pull upward, not downward, as in your video. Thanks for proving my point."

    Eric just to be clear .The ends of two bones appear in the picture, one on the left and one on the right . My understanding is that the bone on the left is the metatarsal head . Do you agree with this ?
     
  28. scotfoot

    scotfoot Well-Known Member

    My comment "Could the collapse configuration of the toes under load be due to "switched off" FDB ; no because the opposite has been demonstrated to happen . Why make up explanations that blatantly disregard the evidence?"
    You reply "Gerry, is that what you intended to write? It is backward to what I am saying.
    The collapse is caused by the switched on EDB and the lack of collapse happens with a switched off EDB. Yes, let's stop ignoring the evidence and move on."


    Eric , in single leg stance the FDB is switched on whether the toes collapse or remain straight. Luke Kelly has demonstrated single leg stance means on. In most people it is entirely an non volitional thing . Stand in single leg stance and if your feet are stronger your toes stay straight, very weak and they collapse.

    You also said -

    "Those three small arrows are in the bone."

    Actually, the three small arrows are "not in the bone" at all but illustrate a fibrocartilaginous pad . (See caption for figure 3b,below )

    You said-

    "That attachment to the bone is at the bottom most arrow. If you draw a line from the bottom most arrow toward the proximal attachment of the muscle you see a line of action of the force that would pull upward, not downward, as in your video. Thanks for proving my point."

    No, not true at all and your thinking here is really quite unfathomable to me .


    Figure 3b. First MTPJ anatomy in a cadaveric specimen. Axial (a), central sagittal (b), and medial sagittal (c) gradient-echo images (5000/10) show how the lateral (L) and medial (M) sesamoids are connected by the ISL (☆). A fibrocartilaginous pad (arrowheads) is seen distal to the ISL, which merges with the medial SPL (black arrow) and lateral SPL (not shown). Dorsally, the EHB tendon (dotted arrow) attaches to the proximal phalanx and lies deep to the EHL tendon (white arrow).

    [​IMG]
     
    Last edited: Oct 20, 2022
  29. efuller

    efuller MVP

    The assumption of hard wiring is not a good one. Hard wiring assumes that with certain input conditions, certain muscles will fire. One of the things that led people to believe in hard wiring was studies done on decerebrate cats. Then they had the decerebrate cats walk down hill and got a different firing pattern. For example, people have a hard time raising one eyebrow without the other. Some people have trained themselves to raise just one.


    Do you have a copy of the Luke Kelly paper?

    It is hard to imagine an experimental set up where you could make the conclusion that EDB is always on when standing.

    Even if you can't selectively activate EDB, this concept does not preclude contraction of the EDB as the cause of toe collapse.


    My mistake, on the metatarsal picture.

    However, that non weight bearing picture still does not justify a 30 degree angle of pull at the MPJ for the model.

    And you still haven't answered this.
    Your explanation of that toe position is that it is caused by muscle weakness. Weak muscles don't move joints. Joints moved to cause the "collapse." My position is that the toe collapse is caused by EDB strength and contraction.
     
  30. scotfoot

    scotfoot Well-Known Member

    The models, both yours and mine, are not representative of the actual situation given the function differences of the MTPJs. The way in which our models function is irrelevant to the question in hand and in fact completely irrelevant to anything I can think of . My model ,minus the reclaimed nuts and bolts, is in the bin and I suggest you do the same with your model.

    Since your model is proof of nothing, due to material structural inaccuracies, what evidence do you have that the hammer toe type collapse seen in the picture is caused by strong contraction of the FDB ?

    When you COM starts to move anteriorly in single leg stance the toes start to apply more pressure to the ground . This additional pressure is developed by contraction of a number of muscles including the FDL and FDB . In the absence of sufficient strength in the FDB, the pull of the FDL will cause the toes to claw or go into a hammer toe configuration, but strong FDB will resist to clawing etc by rotating the base of the proximal phalanx inferiorly around the head of the metatarsal .
    [​IMG]

    Re Kelly, I had his 2012 paper in mind but can only find the abstract . I will keep looking .

    What foot strengthening exercises to you tell your patients to use? I get the impression you are not confident about answering this question.
     
  31. scotfoot

    scotfoot Well-Known Member

    Hi Eric ,

    Here is a link to a very recent paper that illustrates large amounts of activity in the FHB during single leg stance and heel raise in single leg stance . The paper illustrates that these toe flexing and arch supporting muscles are very much involved (switched on ) during these activities .

    Link to Ridge et al 2022
    https://www.researchgate.net/public...t_Muscles_during_Functional_Standing_Postures

    As I have said, I have anecdotally observed that people who are more active have straight toes during single leg stance but inactive people tend have collapsed toes ( toes in a hammer toe like position when under load ). This is when no training is involved .

    Your idea, that straight toes means an inactive FDB, is not supported by any evidence I am aware of .



    Graph from paper. BLS means bilateral stance and SLS means single leg stance . In single leg stance FHB ( in red ) is active to spread load across the foot, aid balance, and support the foot arch .

    upload_2022-10-23_10-55-38.png upload_2022-10-23_10-55-38.png
     
  32. efuller

    efuller MVP

    I don't understand what you mean by function differences of MTPJ's. Both our models can reproduce forces on the "bones" of the toes that would be similar to reality. When the model reproduces something that occurs in reality, that is a sign that it is a good model. Can you explain the difference in function between our models and reality and why do you think it is different enough to discard the models?


    Yes, the FDB causes flexion of the MTPJ non weight bearing, but things change when weight bearing. Free body diagram analysis shows that moment from tension in the FDB tendon is much greater at the PIPJ than the MPJ. This is borne out by what you see in my video when the FDB tendon was on top. The MPJ did not move until the PIPJ was at its end of range of motion. This changed the effective lever arm of the tendon at the MPJ.

    When weight bearing, plantar flexion of the PIPJ increases ground reaction force at the head of the intermediate phalanx. This upward force creates a dorsiflexion moment at both the PIPJ and the MPJ. At the PIPJ the plantar flexion moment from the tendon is greater that the dorsiflexion moment from ground reactive force. At the MTPJ it is difficult to calculate the net moment (Dorsiflexion from ground reaction force and plantar flexion from tendon.) One reason this calculation is difficult is that it is hard to take into account the moment from the tendon pulley/ sheath. Our models illustrate how if you manipulate the leverage of the tendon at the MPJ the effect changes. When the moment from ground reaction force on the toe is greater than the plantar flexion moment from the tendon then there will be a net dorsiflexion moment at the MPJ and the proximal phalanx will dorsiflex at the MPJ. However, if you change the angle of pull of the tendon so that it has a greater plantar flexion moment there will be a point at which the plantar flexion moment is equal to the dorsiflexion moment and there will be no motion, like there was in your video. (Another thing you can maipulate is the amount of ground reaction force. If you hold the model up in the air, and don't press down hard, you would be decreasing the amount of ground reaction force.) Gerry don't discard your model. And don't ignore the evidence even if produces evidence that is counter to what you believe.



    Not relevant to our discussion
     
  33. efuller

    efuller MVP

    "

    Gerry, you said in post #68 "Luke Kelly has demonstrated single leg stance means on. In most people it is entirely an non volitional thing ." The graph shows 80% activity. 80% is not 100%. This does support my idea that EDB being off, or at least decreased, is consistent with straight toes.

    Gerry you are also just focusing on what happens after strengthening . But why do the toes collapse before the strengthening. Before the strengthening and single leg standing the toes were straight. When single leg standing is initiated something causes the toes to collapse. Muscle weakness does not cause the motion of collapse.
     
  34. scotfoot

    scotfoot Well-Known Member


    I believe my model is more accurate than yours with regard to mechanics and force generation esp. at the MTPJ( I am ignoring the demonstration you showed on your video and assuming that you got similar results with the version that includes a ring very close to the axis of rotation between the metatarsal and phalangeal bone) . However, I would not trust my model over in vivo observations.

    Not sure what you mean here . In bilateral stance the toes are flat and there is little activity in the FDB . Once an individual moves to single leg stance the FDB activity shoots up to 80% MVIC . The increase in activity is an average ,it happens for all ,it's just that in people with weaker feet its not enough to keep their toes straight under load because they collapse . Stronger feet don't collapse.

    For clarity ,a hypothetical group of 100 people stand in single leg stance . On average the activity in the FDB is 80% MVIC right across the board . My observations suggest that those with weak feet will have toe collapse those with stronger feet won't.

    No, before strengthening and single leg standing the toes were collapsed not straight . With strengthening comes the ability to keep straight toes.
    If, under supervision , you ask one of your older, less active, pts to stand on one leg and then posture forwards so that their toes are fully loaded you will see collapse . If you ask them strengthen their toes using appropriate exercises ( you won't tell us what exercises you use ) and get them to repeat the procedure you will see that the toes remain straight.

    What I have found ,anecdotally , is that the more you load the toes the greater the strength that is required to keep the toes straight under that load.

    Could you provide a link to this " free body diagram analysis " you reference ? If the analysis is your own could you post it ?
     
  35. efuller

    efuller MVP

    Some irrelevant info was cut from the above quote.

    First problem:
    Person is sitting and toes are straight. Person stands on one foot and toes collapse. My position: When standing on one foot the FDB muscle contracts and causes toe collapse.

    Why do the toes collapse before strengthening if it is not FDB? You have said the collapse is from muscle weakness. This cannot be, because in the change from sitting to single leg standing more muscles are active and the toes change position from when the person was sitting. Muscle weakness does not cause motion. Contraction of a muscle caused the toes to collapse. The most likely candidate is FDB. A plausible model of FDB has created the exact same "collapse". (Where we disagree on plausibility is the angle of pull of FDB at the MPJ. The model with my assumptions reflects what happens in vivo.)


    Second problem:
    After muscle strengthening, anecdotally, the toes that were collapsing are no longer collapsing.
    One possible explanation: The muscle that caused the collapse, FDB, is less active/ produces less force in the tendon, and the toes do not collapse.
    Second possible explanation: there is an increase in net plantar flexion moment at the MPJ from some other source that resist the dorsiflexion moment from (the plantar flexion of PIPJ causing increased) ground reaction force at the head of the intermediate phalanx. One possible source would be the lumbrical muscles. The lumbrical muscles act to plantar flex the MPJ and dorsiflex the IPJs
     
    Last edited: Oct 24, 2022
  36. scotfoot

    scotfoot Well-Known Member

    If you have access to a "free body diagram analysis" that shows "moment from tension in the FDB tendon is much greater at the PIPJ than the MPJ." I should very like to see it please .
     
  37. scotfoot

    scotfoot Well-Known Member

    Ok Eric ,
    If you won't let us see your "free body diagram analysis" I can only assume you did it yourself . That being the cases it will probably contain the same errors as your wooden models so you have no evidence to back your stated theory.

    Not likely . Look at the figure below . It is of the 1st MTPJ but likely the angle of pull of the FDL and FDB of the lesser toe MTPJ's are similar to the angle illustrated for the FHL and FHB . So an angle of about 45 degrees. Note also that the moment arm that can be calculated for the FHB in this picture and so likely for the FDB in the lesser toes ,is much larger than allowed for in your models, where it is almost nil .

    [​IMG]

    Try this - Two people sitting and their toes are straight . One has strong feet one weak feet . They both stand on one foot . The person with the healthier toes still has straight toes and the person with weak toes has collapse toes . That has been my experience and your position makes no sense.

    In the quote below you say that with lots going on in the foot a strong lumbrical might overcome net plantarflexion at the MTPJ ie resist "collapse" . By inference you are saying weakness of the lumbricals might allow collapse . So with muscle weakness comes motion in a multiforce situation . That is what I am saying also.

    You are saying " Muscle weakness does not cause motion" and then say loading feet with weak lumbricals might cause collapse ( motion ) . It seems perfectly clear to me that you are contradicting yourself.

     
  38. efuller

    efuller MVP

    Yes, they were my drawings. If you are not going to accept before looking at them, there's no point in posting them.

    Draw an intermediate phalanx with a proximally directed force from the tendon and a distally directed force from the proximal phalanx applied at the center of the joint.

    Now draw the proximal phalanx with a proximally directed force from the base of the intermediate phalanx applied to the head of the proximal phalanx. Then draw a distally directed force from the metatarsal head to the base of the proximal phalanx. The lines of action of the forces applied to intermediate phalanx are much farther apart than the lines of actions of the forces applied to the proximal phalanx.


    Gerry, are you saying that the model in my video did not reproduce the position of collapsed toes?


    Gerry, the flaw in your logic is going from "allow" to "cause." When the weak muscle allows the motion, something else is causing the motion. FDB

    I tried your experiment with single leg standing with gradually increasing load on the forefoot. In single leg stance, with the heel on the ground, my toes were straight. I flexed a muscle in my foot and was able to collapse my toes. Then I relaxed a muscle and the toes straightened. Then as I put more weight on my forefoot it became much harder to collapse my toes.
    It made me realize that there is a third possibility of a plantar flexion moment at the mpj preventing toe collapse. Tension in the plantar fascia will increase with increased forefoot loading and this creates a plantar flexion moment at the MPJ.
     
  39. scotfoot

    scotfoot Well-Known Member

    No, I am saying your model has almost no moment arm for the FDB and this is not at all accurate.

    Ok ,FDL .


    Research shows that as you move your weight fowards and go into a single leg calf raise, you greatly increase activity in the FDB and this probably makes it hard to collapse the foot .It's perhaps even a bit hazardous to do it on purpose. I wouldn't recommend you try.

    Also, research shows if you want to exercise and strengthen the FDB it is best to do so with straight toes moving around the MTPJ . Bending the toes at the interphalangeal joints engages the FDB less, not more.
     
  40. efuller

    efuller MVP

    And your evidence for lever arm at the MPJ for FDB is????

    Don't show the non weight bearing picture of the first MPJ. Weight bearing will compress the tissues plantar to the metatarsal head and move the tendon much closer to the metatarsal.

    We are arguing over the lever arm of FDB at the MPJ. One way to solve this is to model the joint and compare what happens in reality. If you assume a small lever arm, the model reproduces the reality of the motions of toe collapse.

    And your evidence for FDL causing toe collapse?

    What is interesting about my model is what happens when you pull on FDL weight bearing. In the video you saw the modeled FDB cause collapse at PIPJ. When you pull on the FDL you get collapse at the DIPJ. Same physics, different joint.
     
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