Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Everything that you are ever going to want to know about running shoes: Running Shoes Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
  2. Have you considered the Critical Thinking and Skeptical Boot Camp, for taking it to the next level? See here for more.
    Dismiss Notice
  3. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

The foot as an inverted cable -stayed bridge

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Jun 8, 2019.

  1. scotfoot

    scotfoot Well-Known Member


    Members do not see these Ads. Sign Up.
    I am not sure if this has been suggested before , but can the foot be viewed as an inverted cable- stayed bridge ?

    Gerry
     
  2. scotfoot

    scotfoot Well-Known Member

    Of course the foot is a highly complex structure and a number of mechanisms are in play as gait progresses .

    However , I believe it is possible to tease out ,as a system within a system , an inverted cable- stayed supportive element ,where the tibialis posterior and peroneals (cable 1 ) support the more proximal part of the arch of the foot and the intrinsics (cable 2) support the more distal part .
     
  3. efuller

    efuller MVP

    Gerry, you should read the works of J.H. Hicks from the 1950's. I learned of the mechanical principles of beam, arch and tied arch from those articles. These are still really good articles. Gerry, since you are such a great autodidact, you should pick up a basic engineering text to see how mechanical engineering principles can be applied to the anatomy of the foot. An engineering text would help you see if there was a difference between a tied arch and an inverted cable stayed bridge.

    Eric
     
  4. scotfoot

    scotfoot Well-Known Member

    Eric ,
    The question was "I am not sure if this has been suggested before , but can the foot be viewed as an inverted cable- stayed bridge ?"

    Has it ?
     
  5. efuller

    efuller MVP

    I looked up cable stayed bridge. The foot can't be viewed as that. What is an inverted cable stayed bridge?

    The nice thing about the Hicks articles is that he explains which anatomical structures act as which part of a beam or tied arch.

    Eric
     
  6. scotfoot

    scotfoot Well-Known Member

    I am not attempting to challenge the existing concepts around a tied arch but to introduce an additional element ,also related to bridge construction , to explain the biomechanics of the foot more fully .

    A cable stayed bridge then . The bits we need are vertical supporting post/pillar ,a stretch of roadway that is attached to the pillar at one end and runs horizontally away from the pillar and two supporting cables attached to the top of the tower and then cable A attached to the road about half way along its length and cable B which is attached to the roadway at its end , furthest away from the pillar .

    In practice the cables support the span of the roadway and prevent it collapsing downwards when load is applied . ( cables attached to the top of the pillar and attached to anchorage would be necessary to balance forces out of course but we don't need that here )

    So if you draw this simple diagram out and then turn your piece of paper through 180 degrees you now have an " inverted cable stayed " structure . Now instead of resisting downward forces the structure best resists upward forces . We can call the distal aspect of the foot the road , the tib post and peroneals cable 1 , and the long toe flexors cable 2 .

    Going back now to the foot as a whole in effect you have a tied arch with two tie beams . Tie beam one is the plantar fascia ,tie beam 2 the extrinsic foot muscles . If you have two tie beams the load is shared .

    In post #2 I said "the intrinsics (cable 2) support the more distal part ." I have changed that as this is a theory under construction .

    Your thoughts please Eric .
     
  7. efuller

    efuller MVP

    Free body diagram analysis would quickly explain why it does not work this way.

    The load on a bridge is caused by gravity pulling toward the center of the Earth. The Earth resists that pull with ground reactive force. There are always both forces acting on one part of a bridge and a foot. A cable stay bridge won't work if you turn it upside down. The cable ties are under tension to hold the road bed up. When you turn it upside down, the cables are pulling the road bed toward collapse.

    Another reason that you can't consider the foot as a cable stay bridge is that there is no anatomical structure that corresponds to the central support.

    Technically the muscles and the plantar fascia are tension members and not beams. When something behaves as a beam part of the structure is under tension and part is under compression.
     
  8. scotfoot

    scotfoot Well-Known Member

    "Technically the muscles and the plantar fascia are tension members and not beams." Noted .

    Let's make the cable stayed structure more manageable by reducing it in size to a viewing platform extending out into the Grand Canyon . It's true that , with the platform construction right side up , the cables will resist gravitational forces , however they will not resist the vertical forces produced by a cable attached to the free end of the viewing platform and pulled vertically upwards by a Sikorsky helicopter (ground reaction forces in this analogy/ model ) . For the cables to resist this force the platform system must be inverted .

    "Another reason that you can't consider the foot as a cable stay bridge is that there is no anatomical structure that corresponds to the central support. "

    I am not saying that the foot should be viewed as an exact anatomical version of a cable stayed- bridge , but rather that ,with regard to the extrinsic foot muscles ,there are close similarities .

    Eric , could I ask you a direct question ? Would you agree that in closed chain , contraction of the tibialis posterior and peroneal muscles will act to cause dorsiflexion of the proximal aspect of the arch of the foot and plantarflexion of the distal aspect of the arch , which in turn will produce a shortening of the distance between the metatarsal heads and the heel ?
    In essence ,the basis of the short foot exercise as described by Janda .

    Gerry
     
  9. scotfoot

    scotfoot Well-Known Member

    Below is a link to a good article from Kevin Kirby . Here is a quote from the article -

    " The posterior tibial and peroneus longus tendons cross plantarly across the arch and cause a forefoot plantarflexion moment, which helps resist longitudinal arch flattening. "

    Along with the tib ant these are the muscles of Jandas short foot exercise .

    New Concepts In Longitudinal Arch Biomechanics | Podiatry Today


    https://www.podiatrytoday.com/new-concepts-longitudinal-arch-biomechanics
    24 May 2018 - Kevin A. Kirby, DPM ... The LALSS is a type of “load-sharing system,” which is a common design in both mechanical and electrical systems.
     
  10. efuller

    efuller MVP

    The line of pull of the tendon has to run plantar to the compression surfaces of the bone to create a plantar flexion moment. Or more precisely, the center of pressure of the articular surfaces.

    Peroneus longus does do this. I have done some modeling of peroneus longus and depending on STJ axis position, by itself, the peroneal muscle can do different things. The peroneus longus will simultaneously create a plantar flexion moment at the first ray and a pronation moment at the STJ. Pronation of the STJ will tend to increase ground reaction force on the first met head which will tend to dorsiflex the first ray. Peroneus longus is fighting against itself at the first ray in terms of arch raising. If it has a small lever arm to cause pronation, the first ray plantar flexory force wins. If it has a large lever arm to cause pronation, you can see dorsiflexion of the first ray from increased ground reaction force on the first met head. So, the peroneus longus, by itself, will not always cause arch raising.

    The posterior tibial muscle is in the perfect place to adduct the forefoot on the rearfoot. It's primary attachment is right in the middle of the navicular, so it's line of action of pull is not on the bottom. By itself, the posterior tibial muscle cannot plantar flex the forefoot on the rearfoot. However, in combination with the peroneus longus muscle, the increased supination moment from the posterior tibial muscle will counter act the direct pronation moment from the peroneus longus muscle and allow the plantar flexion moment from the peroneus longus muscle to create first ray plantar flexion.

    The perneus brevis muscle cannot raise the arch because its line of action is not plantar enough.
     
  11. efuller

    efuller MVP

    The anterior tibial muscle because of its line of pull will dorsiflex the forefoot on the rearfoot. However, in stance, the anterior tibial muscle will create a dorsiflexion moment at the ankle joint that will tend to shift the ground reaction force posterior and this will decrease the dorsiflexion moment from ground reaction force on the forefoot. (This would also help peroneus longus plantar flex the forefoot).
     
  12. scotfoot

    scotfoot Well-Known Member

    When the intrinsic toe flexors such as the flexor hallucis brevis and abductor hallucis contract , they will flex the toes . In closed chain (foot on the ground ) this will tend to dorsiflex the forefoot on the rearfoot potentially reducing the force with which the toes can be pressed into the ground . However , the tibialis posterior , peroneus longus and tibialis anterior can act to resist dorsiflexion of the forefoot (see above ) thus potentiating the effects of the toe flexors .

    In effect , in this instance but not all , we have the prime movers acting to maintain the "foot core" and the intrinsics acting as the "prime movers "
     
  13. efuller

    efuller MVP

    The abductor hallucis muscle plantar flexes the forefoot. Whether the attempt to plantar flex the toes does anything to the arch depends on what other muscles are acting.
     
  14. scotfoot

    scotfoot Well-Known Member



    "The abductor hallucis muscle plantar flexes the forefoot."


    I had always thought the same but in this video (below ) the toe flexors lift the ball of the foot , and hence the met heads , up clear of the ground . The angle of the foot as a whole has changed but has the forefoot plantar flexed on the rearfoot ?



    Janda Short-Foot Exercise - YouTube



    upload_2019-6-20_21-17-52.jpeg ▶ 0:24
    19 Apr 2017 - Uploaded by Testosterone NationAnkle position can affect gait and can sometimes be worsened in individuals who walk and/or run with a ...
     
  15. scotfoot

    scotfoot Well-Known Member

    Eric
    Have a look at the short ( 16 second ) video included with this paper , which shows the effects of electrical stimulation of the abductor hallucis ( the video is down near the conclusion section and is listed as -"Additional file 1 ; Exemplar response to an early 15s WPHF train " ) . The toe is suspended in a sling and although plantar flexion forces are not recorded you can clearly see the hallux being abducted . But no apparent arch shortening of the foot arch !
    1. Wide-pulse, high-frequency, low-intensity neuromuscular ...

      https://jfootankleres.biomedcentral.com/articles/10.1186/s13047-018-0258-1
      03/05/2018 · Wide-pulse, high-frequency, low-intensity neuromuscular electrical stimulation has potential for targeted strengthening of an intrinsic foot muscle: a feasibility study
      • Author: Darren C. James, Matthew C. Solan, Katya N. Mileva
      • Publish Year: 2018
     
  16. efuller

    efuller MVP

    I believe there is a force transducer connected to the sling. The study talks about force time integrals. I don't see any other location where they could be measuring force.

    Moments. The abductor hallucis is creating a plantar flexion moment at the MPJ and at the midfoot. The force from the sling on the toe is creating a dorsiflexion moment at the MPJ and the midfoot. The muscle is also creating an abduction moment and the sling is not in position to resist that moment. Things will move when there is a net moment. You cannot conclude from this set up that abductor hallucis muscle does not create a plantar flexion moment at the midfoot.
     
  17. scotfoot

    scotfoot Well-Known Member

    Can the abductor hallucis create a plantar flexion moment at the midfoot without creating a plantarflexion moment at the MPJ ?
     
  18. efuller

    efuller MVP

    No, the line of action of pull of the muscle is plantar to both joints.
     
    • Optimistic Optimistic x 1
    • List
  19. scotfoot

    scotfoot Well-Known Member

    Eric ,
    Are we agreed then , that the exercise shown in this video (see link below ) , in which the foot is shortened ,is primarily about the activation of the extrinsic foot muscles rather than the intrinsic foot muscles , since there is no plantar moment being generated at the MPJs ?

    Link

    Short foot exercise - YouTube



    upload_2019-6-26_18-55-4.jpeg ▶ 0:19
    18 May 2016 - Uploaded by TrackActiveAn exercise for training the plantar intrinsic muscles. Start position: Sitting on a chair with your foot on the floor ...
     
    • Informative Informative x 1
    • List
  20. efuller

    efuller MVP

    What makes you think there is no plantar flexion moment generated?
     
  21. scotfoot

    scotfoot Well-Known Member

    I will rephrase the question .
    Are we agreed then , that the exercise shown in this video (see link below ) , in which the foot is shortened ,is primarily about the activation of the extrinsic foot muscles rather than the intrinsic foot muscles ,IF there is no plantar moment being generated at the MPJs ?
     
  22. efuller

    efuller MVP

    Too many variables and too many unknowns. To answer that you would need to know the moments generated at each joint the muscle crosses for a given activation, and you would need to know the relative amount of activation of each of those muscles. I don't think you can assume that each person would activate each muscle the same amount when a person tries to mimic a foot position seen in a video.

    Your revised question is asking is it primarily the extrinsics if the intrinsics are not active. The answer to that would be yes. However, in the video it appears that the abductor hallucis is contracting in one particular attempt. Does it always contract? Too many variables and too many unknowns.
     
  23. scotfoot

    scotfoot Well-Known Member

    Here is a video from another recent thread .
    The person in the video is demonstrating the short foot exercise as Janda recommended , that is with relaxed toes . You can see the foot go into the short foot position and the toes then being wiggled without the overall position being affected .If Janda thought his exercise was about the intrinsics then he was incorrect since contracting the toe flexors will creating moments around the MFJs and this cannot be done whilst also keeping the same joints relaxed .

    Performing The Short Foot Exercise Properly - YouTube



    upload_2019-6-28_10-38-38.jpeg ▶ 0:54
    26 Jul 2014 - Uploaded by CPCinfoThe ability to perform this short foot exercise is an important factor when learning how to use the entire foot to ...
     
  24. efuller

    efuller MVP

    It wouldn't be the first time someone was mistaken about what they thought they were doing. By the way, MTPJ or MPJ. Phalageal starts with a P.
     
  25. scotfoot

    scotfoot Well-Known Member

    This from Dr Kevin Kirby ,in 2016 , in response to a post of mine . ( And yes Eric , I am sure Kevin knows clinically is not spelled with three i's . It's a typo not normally worthy of any comment )


    "Gerrard:

    The short foot exercise (SFE), as I understand it, involves raising of the medial longitudinal arch (MLA) of the foot while weightbearing, without using the digital flexors. Since this exercise involves joint motions, then it would be considered an isotonic exercise, not an isometric exercise.

    In addition, the motions done during the SFE are likely more due to the contractile activity of the posterior tibial and anterior tibial muscles, not due to the plantar intrinsic muscles, regardless of what is written over and over again on the internet. The plantar intrinsics simply don't have the strength to raise the MLA of the foot by themselves if the individual is standing on their feet and have their forefoot bearing more ground reaction force than the rearfoot.

    The plantar fascia is actually under the greatest tension force around the instant of heel lift during gait. The tension force within the plantar fascia was directly measured in a study over a decade ago in a dynamic cadaver gait simulator at the Penn State Biomechanics Lab by Erdemir et al (Erdimir A, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA: Dynamic loading of the plantar aponeurosis in walking. JBJS, 86A:546-552, 2004). See attached paper.

    As far as intrinsic muscle strengthening, this probably helps some people with plantar fasciitis and is something I use on some of my patients. The problem is trying to get people to consistently do these exercises. The plantar intrinsic muscles are active in late midstance and propulsion and help reduce the strain on the plantar fascia since they all share common MLA-supporting functions. However, foot orthoses and plantar arch strapping are, in my experience, much more effective cliniically at reducing the symptoms of plantar fasciitis than "foot strengthening programs".​
    Cheers,

    Kevin
    **************************************************
    Kevin A. Kirby, DPM
    Adjunct Associate Professor
    Department of Applied Biomechanics
    California School of Podiatric Medicine at Samuel Merritt College"
     
  26. scotfoot

    scotfoot Well-Known Member

    Is there direct evidence that the tibialis anterior and peroneals are central to the short foot exercise ? Yes ,please see the link below to a recent study ( H Yoon et al 2017) .

    The researchers took care to make sure that subjects activated the abductor hallucis in the exercise , so although the toes remained straight they would have have exerted pressure on the ground .

    Maximum voluntary isometric contraction for the tibialis anterior and peroneus longus was recorded for each subject . Subsequent results showed an EMG in the peroneus longus of 46.34±22.76 5 of MVIC for flat footed individuals with the ankle plantarflexed , and of 51.45±14.54 with the ankle dorsiflexed . See table 2 in the paper .

    That level of activation is enough produce a progressive strengthening response in the peroneus longus .


    Link to paper
    Comparison of the Foot Muscle EMG and Medial ... - ScienceCentral


    https://www.e-sciencecentral.org/articles/SC000026926
    by H Yoon - ‎2017 - ‎Related articlesThe short foot exercise (SFE) is effective in increasing the height of the MLA for people with flat feet. Most of the research related to the SFE has simply evaluated the efficiency of the exercise using enhanced ABH electromyography (EMG) activation.
     
Loading...

Share This Page