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.

Shock attenuation? subtalar pronation?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by kerstin, Jul 16, 2010.

  1. kerstin

    kerstin Active Member

    Members do not see these Ads. Sign Up.
    Stride lenght helps shock attenuation but how important is initial subtalar pronation mouvement in shock attenuation??

  2. kerstin

    kerstin Active Member

    Do you believe we don't need initial subtalar pronation??


  3. Kerstin, this is a strange question. I'm not sure why you should ask me this based on the paper I linked you to? Do we need initial subtalar pronation for what activity?
  4. kerstin

    kerstin Active Member

    Ok, of course because I believe (but can be wrong, mmm ;-)) we need initial pronation, not only for running (for almost every sport where we have high impact forces). Because using the initial pronation range will distribuate the impact forces on the articulations, which will decrease cartilage damage. Also the vibrations will be less on soft tissue.
    But when I see patiënts with chronical pain (like achilles tendinopathie or tibial posterior periostitis,... ), I often see that the body reacts by overstabilisation (for less traction on the muscles), so no mouvement in the subtalar joint. Even we expect by doing the measurements that they need to compansate by subtalar pronation. But of course, then the question raise is it the egg or the chicken who was first? And then the question how important is that initial pronation?
    So need some discussion.
  5. Kirsten, as both the gastrocnemius-soleus via the achilles tendon and the tibialis posterior generate internal supination moment at the subtalar joint, any increase in stiffness in these musculo-tendonous units will potentially increase the supination moment and maybe decrease the amount of pronation.
  6. kerstin

    kerstin Active Member

    yes that's for sure but is it the supination that cause the problem or is it the expected compensational pronation that cause the problem. For example when I measure a forefoot varus of 10° an hypermobile 1st ray I would expect a pronation as compensation but the gait analysis gives a light supinated gait patern without any subtalar pronation, but as compensation a high pressure on the lateral forefoot. Is that gait patern a protection for the pain or the problem. And for the therapie should you increase subtalar pronation by heel strike??? Or is that lack of pronation no discussion because you don't need it for shock attinuation??

  7. Kerstin:

    Hope you and all my other friends from Belgium are doing well.

    You raise an interesting question regarding the idea that subtalar joint (STJ) pronation at the time of heel contact in walking and running may be an important shock absorbing mechanism for the body. This concept was certainly taught to us by all the faculty in Biomechanics at the California College of Podiatric Medicine (Drs. Root, Weed, Valmassy, Smith, Blake, etc), but to my knowledge, this concept has not been experimentally verified, but it certainly seems mechanically logical.

    By far, the most important shock absorbing mechanism in running is the lowering of the center of mass during the first half of support phase that is accomplished kinematically by knee joint flexion and ankle joint dorsiflexion. Even though STJ pronation does occur in the first half of support phase, and I believe is important to reduce the shock of foot contact, especially in rearfoot strikers, this mechanism is not near as important as knee flexion and ankle dorsiflexion.

    I believe that the reason it is advantagous to have some STJ pronation during running is that is helps convert some of the downward directed forces from heel contact to internal rotation moments on the tibia and femur, which should help attenuate the shock of ground contact to some extent. This hypothesis, however, has not been supported by scientific research, to my knowledge.

    I also believe that for similar mechanisms, STJ pronation is desirable for the contact phase of walking gait since it will help lower the center of mass and also induce internal rotation of the limb that is contacting the ground. Again, this has not been supported by scientific research. However, in my clinical experience, making an orthosis for the patient that is maximally pronated at the STJ at heel contact and allowing them to undergo pronation motion at heel contact again by making them less pronated at heel strike with a foot orthosis will, invariably, help relieve many postural problems for them over time.

    Again this is a great question that requires much further research and hopefully will stimulate further comments from many of our fine contributors here on Podiatry Arena.
  8. kerstin

    kerstin Active Member

    Hi Kevin,

    Yes ev'ting goes well over here. Thanks.
    That's what I am thinking too, it is defintly important but it's so difficult to judge right because I believe that there are several reasons why patiënts doesn't pronate. And in some cases you beter should not let them pronate. So you know you're next research topic ;).


  9. Kevin, I linked to a paper at the start of this thread which demonstrates that: "impact loading was increased when normal pronation was prevented during running."

    Agreed, add hip flexion to that list too. I think that increasing knee flexion increases ankle dorsiflexion and foot pronation. Viz, the knee joint kinematics determine (to an extent) the ankle and foot kinematics. Or, is it that increasing foot pronation, increases ankle dorsiflexion which then pulls the knee into greater flexion? You seem to be advocating this "distal to proximal" direction, Kevin:

    Which brings us back to the direction of power flow...

    Kirsten, in regard to structural foot-types, i.e forefoot varus etc, remember that the position and motion of a joint segment is determined by both the internal and external moments acting about the joint axes.
  10. Looking at figure 6 in the Van den Bogart paper http://www.podiatry-arena.com/podiatry-forum/showpost.php?p=152036&postcount=5 there seems to be an initial positive spike 0-10% in the majority of male subjects during running indicating a distal to proximal power flow- foot driving leg, but in females this is less obvious- why the gender difference? But up to about 50% of the contact phase where the leg "spring" is compressing, in pretty much all of the females the power curve is negative, indicating that the tibia is "driving the foot" in females during the first half of the contact phase of female runners. The male data appears more random. Why the gender differences?
  11. kerstin

    kerstin Active Member

    I must say that I don't see lots of patients who has an external moment on the STJ when they have an forefoot varus of 10°. Most of the forefoot varus types isn't even structural.
    But do you use the test of Kevin to determine the axis??


  12. Kerstin, whenever there is a ground reaction force there is an external moment acting on the STJ. And, by definition forefoot varus is a structural deformity.

    Do I use the test of Kevin? Not too much, these days.
  13. kerstin

    kerstin Active Member

    yep and mosly also an internal moment, but I mean more internal moment because of compensation?
    And I am not agree, that there are only structural forefoot varus types, you have also a functional forefoot varus as adaptation of soft tissue through ground reaction forces agains the medial forefoot.


  14. In order to bring about equilibrium, internal moment needs to match the external moment in an opposite direction. So, if we strike the ground and the subtalar joint pronates due to external moment from ground reaction force, then there needs to be an equal and opposite internal supination moment in order to arrest the motion.- the subtalar joint doesn't continue to pronate forever- right? So why is the magnitude of one moment (external or internal) more important than the other? Well, if the external moment is too great, then the stress in the tissues generating internal moment to bring about equilibrium may be too great also, leading to excessive tissue stress = injury, so ultimately the external moment is key (which is how and why foot orthoses work). Forefoot varus is a fixed osseous deformity in which the forefoot is inverted relative to the rearfoot when the subtalar joint is in neutral, defined by Root. You are talking about forefoot supinatus. Forefoot varus and forefoot supinatus are not the same thing.
  15. kerstin

    kerstin Active Member

    oeps yeh, right forefoot supination :hammer:
  16. kerstin

    kerstin Active Member

    and again :hammer:, more external STJ moment with forefoot varus and more internal MTJ moment, brrr help need some holiday (flemish brain twist) :D
  17. kerstin

    kerstin Active Member

    to come back on shock attenuation. Let's say we don't need that initial pronation but we see a patient who has lack of shock attenuation what do you do?? or do you think there aren't any injuries related to lack of shock attenuation?
  18. Thanks for that one, Simon. I had never seen that one before. Anyone have the full text version of the article for us?
    Like a spring that can compress and then recoil to absorb shock in a vehicle suspension system, our body has several kinematic mechanisms by which to dissipate the forces of impact. As we have already established, ankle joint dorsiflexion, knee flexion and hip flexion are the main ones but also it is quite likely that medial longitudinal arch flattening and subtalar joint pronation play lesser, but still significant roles. As long as the kinematic system can increase the duration of time over which the energy is absobed from ground impact, then impact force will be dimished. I would think that subtalar joint pronation, which coexists with medial longitudinal arch flattening and occurs with tibial and femoral internal rotation would be significant enough to increase the shock-absorbing capability of the human foot and lower extremity during both walking and running.
  19. kerstin

    kerstin Active Member

    I follow you completly Kevin.
    And indeed it would be nice to read the full text.
    Thanks for the other article too, still need to read it.

  20. Kerstin:

    You owe me a Belgian waffle.;)
  21. kerstin

    kerstin Active Member

    Yep, deal (can also bring the sugar for Pam :)).
    Thanks for the paper.

  22. markjohconley

    markjohconley Well-Known Member

    Exactly what I was telling my student yesterday...... Jeez Simon, when I grow up I wanna be just like you!
  23. Dr. Spooner:

    But my biomechanics professors at CCPM taught me that foot orthoses worked by causing the the subtalar joint to function in the neutral position, by preventing compensation for forefoot to rearfoot deformities and by locking the midtarsal joint! Biomechanics has sure changed a lot since podiatry school!!:wacko::rolleyes::drinks

    Thank God!!!
  24. Timm

    Timm Active Member

    Unfortunately for me and many more future podiatrists, this approach to biomechanics is still being taught in Podiatry schools (well it was up to November 2009 when I graduated from uni here in Australia).
    That is why I am grateful for the contributions from everyone on PodArena who take the time to impart their knowledge on the rest of us. Also looking very much forward to the Bootcamp in Melb in Oct, although I suspect I will leave with a small headache each Tuesday evening!!!
    Again, thankyou all :drinks
  25. Just reading through the thread again. Kerstin or someone else. Kerstin can you explain this comment. To be honest I don´t get the link between GRF having an effect on the STJ which would mean the MTJ has more internal moments.
    Can you explain ?

    In my eyes GRF or external moment, will effect both the STJ and MTJ but will effect them differently dependent on the axis position etc. But as Simon says the force must be equal and opposite when equilibrium is acheived.

    As we now understand the STJ and MTJ will be influenced by each other but are independent, so again I don´t see the more "external STJ moment with forefoot varus and more internal MTJ moment" as you wrote.

    If your meaing that in a person with a FF supinatus ( soft tissue contractor) the inversion of the FF indicates that the moment is internal ?

    I think that GRF will be the most likely cause of the FF supinatus deformity.

    Heres some reading http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=7822
  26. Isn't it time we let everyone know the truth, Mark? Mark and I are identical twins that were separated at birth, in order to keep us safe from our father, the evil Lord Vader.
  27. markjohconley

    markjohconley Well-Known Member

    I'd certainly look better in a mask! ... and not quite identical
  28. kerstin

    kerstin Active Member

    Hello Micheal,

    So when there is a long and increased STJ pronation mouvement then you have an external force acting on that axis and this can cause a FF supinatus because the GRF is pressing the FF into supination which I would say there is an internal moment acting around MTJ. So then the external STJ force is the cause.

    When I see a FF varus structural then there is, starting from midstance, a more external moment on the MTJ and then there is even a more internal moment on the STJ axis (but this is not always the case, this depends on where the compensation will take place). But this will also depends on axis position and mobility of the STJ. Right?
    And by writing this down, the assumtion of STJ pronation with a structural FF varus is a bit over, mmm OK thx.

    And Simon, how do you change the moments when you don't change position?

  29. Griff

    Griff Moderator

    I used to really struggle with how there were changing moments/forces if there was no change in position/kinematics. And then one day Spooner rocked my world with a story about fat kids on a see-saw. Hope he tells it again here...
  30. Go ahead Ian, I'm real busy preparing for summer school right now.
  31. Just lean against a free-standing brick wall some day.

    Did the wall move when you leaned against it and applied a force to the wall? Most likely not.

    Did you change the moment acting across the wall-ground interface when you leaned against it? Yes.

    Did the moments and forces acting on the wall change but the wall had no perceptible change in its kinematics? Yes.

    This type of demonstration is one that I have been doing over the past 15 years of lecturing on this important subject.

    The physics lesson to be learned here? Just because there is no perceptible change in rotational motion across one of the joints of the body doesn't also mean that the moments have not changed across that joint.
  32. kerstin

    kerstin Active Member

    Hi Kevin,

    OK when it isn't a fixed brick wall and I lean on it, it will definitely change a lot. And the STJ isn't a fixed joint, it can move, so by changing position, you have an impact on the moment of STJ axis. But on the other hand, it's not because we don't see a change that there isn't any change of the moment acting on that joint. But from my experience most of my patient have a change in position when the problem is around STJ axis. So I really thing we can change position and so we influence the moments acting on the joints.

    Just a question, when you see a child who has excessive STJ pronation from heelcontact till propulsion and you change the moments on the STJ axis with orthotics (so you control the pronation mouvement) but there is no visable change in position on the STJ , I would say that there is still a problem because when they stop wearing there orthotics they will fall again in there old pattern?? So no possitive effect??


  33. Craig Payne

    Craig Payne Moderator

    Just to add to this thread ... i vaguely recall a paper from ~10 or so yrs ago that looked at 'shock absorption' while running on a camber ... ie one foot would have been more 'supinated' and one foot more 'pronated' ... if I recall correctly, that found no difference between the legs which raised questions re the "pronation" actually assisting in impacts .... I think ...
  34. What would have been vary intersting if they looked at knee flexion with the 2 different positions, to see if there was a change...........
  35. Kerstin:

    The subtalar joint (STJ) is free to move....until it reaches its end range of motion. What happens to the STJ when it is in its maximally pronated and then an external STJ pronation moment is applied to it by ground reaction force acting lateral to the STJ axis??

    Does the application of an external pronation moment acting on a maximally pronated STJ cause additional STJ pronation or does the pronation moment cause no STJ motion?

    Answer? (Kirby KA: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989.)
  36. kerstin

    kerstin Active Member

    Hello Kevin,

    when maximal STJ pronation is achieved there will be no additional STJ motion but the external force acting on the STJ joint increase.
    But when I correct the foot I put an internal force on the STJ axis so I will not reach the end of STJ ROM. And by doing this I change the STJ position.


  37. Kerstin I beleive and I could be wrong. I think your getting some of the terms a bit mixed up.

    External moments are Forces like Ground reaction force (GRF), Orthotic reaction force (ORF)ie something which comes from outside the body.

    Internal moments are Forces from muscles, ligaments ie from inside the body.

    A moment is a force placed on a joint.

    Motion is movement of the joint.

    You don´t have to have a change in motion if there is a change in moments. The change in moments must be greater that the opposite force on the joint to get any movement.

    If we take a basic look at the Subtalar joint and in this case the Peronus Brevis (PB) muscle and GRF medial to the STJ axis. That all we should think about at this stage.

    GRF - STJ&STJ axis - PB

    If the STJ is not pronated and or supinated for our 1st example, when the PB contracts the STJ will pronate an internal pronation moment, if this moment is higher that the supination moments on the STJ the foot will pronate ( motion).

    Now if we say that the STJ pronates so much that the STJ is maxially pronated, the STJ axis will have medially deviated ( and others things as well), when the motion stops the foot is in balance or equilibrium. For us in this basic STJ it would mean that the force moments on the STJ from the PB (Internal STJ pronation moment ) and the GRF ( External STJ supination moment) and equal and opposite.

    Now in this maximally pronated foot, if the PB continues to contract the PB will still placing a force on the STJ , (an internal moment), but due to the GRF moment ( the external moment) being so large there is no motion at the STJ or change in STJ axis.

    ok now we add a new Force to our simple STJ example the orthotic or ORF, by a medial skive device. Really what we are doing is bringing the ground up to the foot.

    By adding the ORF ( another external moment) we change the balance between the supination and pronation side. In most cases the increase in supination moments from the ORF we will get STJ supination motion and a change in the STJ axis which will then become more laterally deviated, until it stops and then we have our new balanced or equilibrium point.

    But if the PB is able to balance the increase in force from the ORF we will have a increase in the STJ external supination moments but no change in motion or STJ axis position.

    Hope that helps some, ´that how I look at things in a basic way.
  38. Griff

    Griff Moderator

  39. Griff

    Griff Moderator


    I think this is the paper you may be talking about:



Share This Page