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Running shoe - dual density harder material location

Discussion in 'Biomechanics, Sports and Foot orthoses' started by markjohconley, Sep 13, 2017.

  1. markjohconley

    markjohconley Well-Known Member

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    Whilst inspecting possible running shoe purchases it seemed the harder mid-sole material of the 'dual density' shoe did not extend to the posterior extent of the mid-sole. It seemed to be located beneath the foot's ILA and not include the medial calcaneal tuberosity. Would this be correct? The Athlete's Foot head salesperson at the shop was unable to provide information. Thanks, Mark
  2. Craig Payne

    Craig Payne Moderator

    That is pretty much the situation.
    Different shoes vary it.
    Would be good to have more variety in it location to get the lever arms needed in individuals
  3. markjohconley

    markjohconley Well-Known Member

    Apart from a rude word and What! and noise of me forehead slapping, I was going to ask whether this indicates that running shoe manufacturers are advocating an arch support-like feature in their 'battle to correct foot posture' but then realised it wouldn't even be capable of altering any foot joint moments (desirable or otherwise) as unless the foot actually contacts the sole ('banana-shaped' foot) then Newton's 3rd law would mean no (equal and) opposite force by the sole on the plantar foot surface. Yes?
  4. efuller

    efuller MVP

    It's good to think of the usual rollover process. At heel contact, with the forefoot up in the air, the center of pressure is relatively close to the STJ axis should have a relatively small moment arm about the STJ. As the foot plantar flexes after contact the ability of the dual density midsole to shift the center of pressure under the foot more medially becomes more necessary and more possible when the denser material is more posterior.
    My guess for why some would move the denser midsole material more anteriorly is to have better cushioning at instant of heel contact. Think back to the old Bobbert and Nigg paper that studied force transients at heel contact.
  5. Mark:

    The dual density midsoles of running shoes, with the higher durometer more medial on the rearfoot midsole, has been around in running shoes for at least 35 years. Currently, dual density midsoles are standard in most "stability" and "motion control" styles of running shoes. I consider them to be "dynamic rearfoot varus wedges" in the midsoles of these running shoes, using the same logic mentioned by Eric.

  6. I also wrote a recent article for Podiatry Management on running shoe biomechanics where I address the history of dual density midsole running shoes.

  7. markjohconley

    markjohconley Well-Known Member

    Prof. Kirby thanks for the article, read it twice, very interesting / informative.

    If the mid-sole was also to increase (external ankle inversion) and STJ supination moments the harder material would have to extend to the mid-sole's posterior surface to include the medial calcaneal tuberosity? as I have the impression that in some / many? dual-density mid-sole shoe brands it does not, mark
  8. Most running shoes do have the higher durometer medial midsole extending posteriorly under the heel if they use a dual-density design in their midsole. However, some do not. I don't think it makes a lot of sense to have the higher durometer midsole only under the midfoot, since the medial midfoot doesn't generally contact the ground during running. I don't design running shoes...if I did, many wouldn't be designed the way they are.
  9. markjohconley

    markjohconley Well-Known Member

    Thanks Eric, I was so 'worked up' about the harder material not extending 'all the way' I missed the obvious.
    I had trouble comprehending, "... time histories of the sum of the segmental contributions were compared to Fz(t) measured ... ".
    I assume Fx(t) is vertical GRF in relation to time. I am only able to access the abstract of, 'Calculation of vertical ground reaction force estimates during running from positional data'.
  10. toomoon

    toomoon Well-Known Member

    Dual density midsole have never been shown to achieve what they purport to.. ever.. that said, the science that has examined this aspect of running footwear has been poor. However, as it stands today, there is zero justification to include a dual density midsole in a shoe.
  11. Using that logic, Simon, what of the hundreds of shoe features that have been included over the years in running shoes has been scientifically examined sufficiently to warrant its inclusion in today's running shoes? I can't think of any. Please name five running shoe features that you feel science has examined adequately to warrant inclusion in all running shoes for all runners.

    Contrary to your belief, I think that the dual-density midsole is one of the best running shoe innovations that has occurred within the past four decades. The dual density midsole is not only a very smart biomechanical design for running shoes, but it has proven, over the years, to be a clinically useful and comfortable shoe sole feature for running shoes. The dual-density midsole provides a "dynamic varus rearfoot wedge" for runners. If dual-density midsoles weren't useful and comfortable for many runners, do you think they would have been used continuously in running shoes for the past 35 years? I doubt it.
  12. toomoon

    toomoon Well-Known Member

    Here was I thinking you would be too busy eating cookies in Amsterdam to bother replying!
    Kevin.. you and I have had this discussion before.. what I have said is there is no evidence to support the concept that dual density midsoles do anything other than add weight. They MIGHT add a little bit of construction integrity, but they do not control motion and they do not prevent pronation or injury. What this 40 odd year old "technology" has done is underline and emphasise an erroneous paradigm, that being that pronation should be controlled. Calling on years of success with this type of shoe is not relevant, because you are not able to titrate this against what might have happened with other designs, geometry for example, that might and should have happened if the indusrty and retail had not been so obsessed with motion control.. put simply, you cannot know!
    In response to "Please name five running shoe features that you feel science has examined adequately to warrant inclusion in all running shoes for all runners" of course you know I can't because there aren't any.. but that does not mean there will not be and especially it does not mean we should cling to weight adding "technology" given we understand weight IS bad. Basically, shoes have been given far more attention than they deserve in response to foot biomechanics and especially injury. They are currently, a very small part of the equation, and dual density midsoles are a dinosaur that should not be part of the discussion.
    Kevin, if you can point me to one single piece of evidence that "The dual-density midsole provides a "dynamic varus rearfoot wedge" for runners" I would be very grateful. And DD midsoles are still around 35 years later because it has been embraced by retai, the publicl and our profession as being something very important. without evidence.
    You would be aware of several studies that cut windows into the back of shoes to measure in shoe pronation. The foot still pronates completely happily inside the shoe with a dual density midsole.. DD midsoles do not systematically or substantially provide a varus wedging effect.
    If you want, I can forward you videos privately of the same runner in the same circumstances running in dual density midsoles vs geometrically manipulated midsoles. If "motion control" is your bag, geometry wins every single time..however, because I DO work in footwear design and research, I can't broadcast some of this stuff publically.. happy to email it to you though. Enjoy Amsterdam and say hello to Pam!
  13. Simon, greatly enjoyed the Rijksmuseum this morning. Ready to head out for some more shopping (mostly for Pam) after dinner. It's now sunny in Amsterdam after a little morning rain.

    I knew you couldn't name five running shoe design features that are scientifically justified in order to only prove the point that this discussion is nothing more than your against my opinion about the usefulness and benefit of dual-density midsoles in running shoes.

    As you know, Benno Nigg's Preferred Motion Pathway Model predicts that rearfoot motion may not change with changes in shoe design. With that being said, I predict that dual-density rearfoot midsoles will eventually be shown to significantly change the kinetics of the rearfoot (i.e. decrease the external rearfoot eversion moments and decrease the internal rearfoot inversion moments) but not significantly change the rearfoot kinematics during running.

    Until then, to only discuss the kinematics of the rearfoot in running in response to running shoe design is to only discuss a fraction of how running shoe design features may alter the efferent activity of the central nervous system during running.

    Time now for dinner, then shopping, then taking evening photos along the canals of Amsterdam!
  14. toomoon

    toomoon Well-Known Member

    I am glad you guys are having fun.. Amsterdam is one of my very favorite cities..but still you do not come to visit me despite being only an hour away.. is it something I said?
    So, you have to believe that we do a LOT of comparative studies against all sorts of running shoes to try to figure out what works and what does not.
    What if I told you that we have a shoe.. super decoupled.. super flexible and light (less than 250 grams).. and its metrics for kinematics and kinetics are so off the chart we have spent 2.5 years trying to disprove what we are seeing.. that this heavily decoupled shoe lowers peak pronation and pronation ROM more effectively than a motion control (dual density) shoe, and that it also radically changes the moments not only at the foot, but at the ankle knee and hip?
    And what if I told you there is also no energetic penalty this (which we thought might be the case because it is so flexible)?
    Would you believe me?
    Because this shoe not only exists, it is going into production quite soon.
    Now enough of this.. go out and spend some money and enjoy dinner...
  15. efuller

    efuller MVP

    When you say the science has been "poor" do you mean that no one has looked to see if dual density midsoles shift the center of pressure under the foot. In a couple of minutes on Pubmed I didn't see any studies on the center of pressure and midsoles. I've walked over an emed with dual density shoes and it sure looked like there was a shift in center of pressure. I will admit that I didn't run the numbers to be sure, but to the eye it looked different. The original Nigg study looked at lateral flare on running shoes and showed an increase in pronation velocity with lateral flares that is easily explained by shift in center of pressure with a bigger lateral flare.

    So there is theoretical justification for use of dual density midsoles. Is there a study that shows that dual density midsoles don't shift center of pressure?
  16. CorneHaast

    CorneHaast Member

    In my humble opinion a very important reason to add a dual density to a midsole is to PREVENT that de midsole is compressed too much by the runner. Sometimes you need a post more at the rear foot (when the calcaneus valgisation is very easy because of very loose ligaments), sometimes more under the mid-foot (when running with the feet pointing outward), and sometimes even at the forefoot (in case of a metaprimus elevatus; in that case I would even prefer a wedgeshaped midsole, but they don't exist). There are somtimes very stabil shoes, on which neutral ánd "overpronating" runners can run without problems. I remember the Asics Nimbus 2 and 5 as good examples. So it is possible to make shoes without medial posts, and still providing a good stabiltiy. I can also remember de Brooks Adrenaline GTS 2, which was only suitible for supinating (!) runners, because of its very instabil characteristics. It did not even give stability to "neutral"runners. And this shoe had a medial post...
    Greetings, Corné, from The Netherlands.
  17. efuller

    efuller MVP

    To translate, the force profile seen when the heel gets the ground, is consistent with the weight of the shank and foot hitting the ground in heel contact running. The rest of the body is gradually decelerated by flexion of the joints.

    As they have shown with the devices that measure hardness, impact accelerations can be reduced by materials at the point of contact. Those German artificial athletes are dropped from a height and the deceleration when the "athlete" hits the material in question is measured. This is one method to measure the hardness of midsole material. So, for the shank, impact forces could be reduced with a softer, but not too soft, material at the posterior aspect of the shoe.
  18. Eric, Simon and Colleagues:

    Since there are no good scientific studies on dual density midsoles and their effects on the shift in center of pressure or rearfoot kinetics during running, I don't see how one can dismiss their effectiveness without some data that supports their opinion that they do little other than "add weight" to the running shoe.

    Certainly, considering their popularity over the years, if dual density midsoles were harmful, or uncomfortable, or produced injury over the past three and a half decades for runners, they would have gone the way of the 20 degree lateral sole flare or the five-toed running shoe...in other words, they would not be around that long. As Craig Payne often says, runners have been voting with their feet for 35 years.

    As a competitive running athlete for 40 years, I can very clearly state that the dual density midsole running shoe was a necessity for me during my competitive years to not have pronation-related injuries. There may be new shoe designs that come and go, but the dual density midsole, in my opinion, is here to stay for many, many more years in running shoes.
  19. toomoon

    toomoon Well-Known Member

    Kevin!! I have not said they directly cause injury. I have said they do nothing except add weight, which is the opinion of most shoe scientists!
    You are presenting your N=1, however, the question remains, how do you know you would have done as well or better in a different configuration?
    DD midsoles have prevailed only because the running shoe companies have so much invested in them. They even have names for them like Duomax. The estimation of most shoe scientists is that motion control shoes with dual density midsoles are suitable for 1 in 500 to 1 in 1000 runners at best.
    Dual Density midsoles have already largely disappeared, with most companies having only 1 to 2 models within their range, and some having none at all. Big companies like ASICS know there is no advantage to DD midsoles because they have tested them, but, as so often happens, once you give a "technology" a name and the public believes the hype, it is very.. very difficult to get rid of.. same with GEL.
    Finally, I do not believe Craig's comments about voting with their feet referred at all to shoes with DD midsoles.. if I remember correctly, it was in relation to the decline in the minimalist craze..!
    very best

    Simon Bartold
    Fellow Faculty of Podiatric Medicine,
    The Royal College of Physicians and Surgeons (Glaasg)
    Fellow, The University of Melbourne, Australia
    Visiting Fellow, The University of Staffordshire, UK
    Director of Strategic Programs Amersports
  20. toomoon

    toomoon Well-Known Member

  21. toomoon

    toomoon Well-Known Member

    Are we talking force or acceleration here Eric? Nigg was able to demonstrate fairly clearly in 2 studies 10 years apart that softer materials did not neccesarily reduce vertical impact force.
    If I could figure out how to insert an image, I would put up those results.. alas, this is beyond me..
  22. Simon:

    Can you provide evidence for your statement "DD midsoles have prevailed only because the running shoe companies have so much invested in them"? I tend to think that is your opinion, not fact.

    The reality is that the running shoe companies could easily quit selling dual density midsole running shoes by eliminating those shoes from their running shoe lineup. That would, in fact, save them money in production costs. But, what would happen if they did that? Many runners would then complain because they are comfortable and seem to allow them to train with less injury, no matter what "shoe scientists" think about how many of them need the shoe.

    Do "shoe scientists", all employed by running shoe companies, know more about what individual runners need than do sports podiatrists, who see the runners who these "shoe scientists" injure with their "latest and greatest" running shoe designs? I'm not so sure. There are plenty of instances where "shoe scientists" have designed shoes that worked great for some runners but didn't sell well because most runners found them uncomfortable or gave them injuries. So much for "shoe science" when it comes to making a great running shoe, in many instances.

    I know dual density midsoles worked best for me because when I was running 70+ miles per week for many years, I would always get medial ankle and knee pain training in non-dual density running shoes. In addition, in the thousands of runners I have treated over the past 32+ years, many of my runner-patients report the same experience. Not everyone does better with dual density midsole shoes, but some, like myself and many of my runner patients, seem to do best with this shoe design feature.

    As I said before, Simon, show me the data that says that dual-density midsoles don't alter the frontal plane kinetics of the rearfoot running and I will be reconsider. Just because dual-density running shoes haven't been shown to alter rearfoot pronation kinematics means very little when we start to discuss the important forces and moments that produce injuries in runners.
  23. toomoon

    toomoon Well-Known Member

  24. efuller

    efuller MVP

    Why do they think that? As a clinical estimate I would tend to put a third of people in anti pronation shoes. Specifically, those with a more medially deviated STJ axis.

    When they did those studies did they just test everybody without trying to differentiate differences between feet. Specifically, did they look at STJ axis position in the transverse plane. I would predict that most of the people would not need dual density midsole shoes. However, I would also predict that those with a more medially deviated STJ axis would prefer the dual density shoes. Feet are different. All people should not wear shoes for the average foot.
  25. efuller

    efuller MVP

    F = ma so those are the same.
    I was talking about just the high frequency force spike seen with heel strikers. Not the total force.

    There is some kinetic information in that study. If the acceleration changed with wider flare shoes the moment at the STJ changed. Which is my point about the dual density shoes. The question is whether dual density shoes change the location of center of pressure compared to shoes without a dual density.

    I'm not sure what you are saying about I could see a change with any shoe. I walked over the force plate with shoes without a dual density and shoes with a dual density. There were higher pressures under the medial heel with the shoes with a dual density midsole. If I remember correctly these were the old Asics with the plug in the medial heel. There was increased pressures right where the plug was.

    I agree that you can shift center of pressure under the heel with other ways than a dual density midsole. The Nike foot bridge is one example. I would need pictures to understand what you are describing above, but I'm sure there are plenty of ways to make a shoe tend to shift the center of pressure under the foot. Some may be lighter than a dual density midsole.

    Simon, do you agree that a shift in the center of pressure under the foot would change the kinetics?

    I also recall experimenting with varus wedges under my orthotics. I eventually put enough wedge under my orthotic that I noticed that my peroneus brevis muscle was starting to contract a lot more. There might not have been any kinematic changes, but that N =1 experience sure helped confirm by belief in the theory of shifting the center under the foot will change the moments about the STJ axis. This illustrates how the kinetics could change without kinematic changes.
  26. toomoon

    toomoon Well-Known Member

    I agree. One of the problems is that the studies never look at STJ axial deviation because that is a discussion podiatrists have, and nearly all these studies are by biomechanists who do not take this into account!
  27. toomoon

    toomoon Well-Known Member

  28. efuller

    efuller MVP


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