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.

MASS - Questions un-answered

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Graham, Dec 1, 2010.

  1. Graham

    Graham RIP

    Members do not see these Ads. Sign Up.


    What are they calibrated to? How do you calibrate these "arch supports"?

    What evidence do you have to support this statement?

    Thanking you in advance
  2. Graham

    Graham RIP

    Please! It would be helpful if you could give these questions some thought.

  3. Graham

    Graham RIP

    Please! It would be helpful if you could give these questions some thought.

    This is my third request on this thread and my fifth attempt overall to have you answer a reasonable question. Please! Could you give this a whirl?

  4. Graham

    Graham RIP

    Please! It would be helpful if you could give these questions some thought.

    This is my fourth request on this thread and my sixth attempt overall to have you answer a reasonable question. Please! Could you give this a whirl?

  5. VernWalther

    VernWalther Member

    This should at least answer the question you posed to Ed about how (& why) he calibrates flexibility...

    Part 3 of Dr. Ed Glaser's morning lecture at the "Competing Theories of Foot Biomechanics" seminar at Rosalind Franklin University on Saturday, November 13th, 2010.

    Vern Walther, C.Ped.
    Last edited by a moderator: Sep 22, 2016
  6. Graham

    Graham RIP

    Ed Glasser Accepts defeat?


    I assume your lack of response to the questions I, and others, have put to you regarding MASS means you accept that this "theory" and approach has no scientific merit and is for your profit and not your clients or their patients? Perhaps?
  7. Graham

    Graham RIP

    thanks..i think! Anything else you can answer for Ed?
  8. Meh.

    Sounds to me like he's talking about supination resistance... without talking about supination resistance. And I'm sure I remember that STA location was more predictive of higher Supination resistance than body mass...
  9. David Wedemeyer

    David Wedemeyer Well-Known Member

    Excellent question Graham.

    Calibration is a nifty marketing term but you'll notice Ed uses the terminology 'accomodation' synonymously with 'posture'. I watched all of the videos supplied by Vern (thank you) of the "Competing Theories of Foot Biomechanics" lecture and I recall Ed mentioning this concept. If you examine a SS insole you'll understand that the suggestion that resupination in midstance is the goal but the devices are too accomodative to actually achieve that. How do you negate a high MLA design insole from becoming (as Ed is often fond of saying) a warranty? Compliance of the device.

    Don't take my word for it, test them for yourself. I bet dollars to doughnuts you'll also find that calibration and accomodation are not scientific derived criteria but synonyms for compliant materials and therefore a compliant (accomodative) device. Ed's lecture supports this.
  10. Anyone who knows me will know that I have more than a passing interest in orthoses calibration. I've tried to avoid this thread, yet here I am. To calibrate an orthosis in terms of it's load/ deformation characteristics we first need to know the loading upon the device during dynamic function- errr we don't/ can't know that from a cast sent to a lab. And inflating bladders with air, on top of an orthosis ain't never going to tell us this. We can inflate an air filled bladder on top of a device and then sand-blast the device so that it deforms a certain amount under the bladder's load, but this is not related to how the device will perform in-vivo because we don't know the loading pattern in-vivo. How much and where should a device deform? Moreover, there are ultimately three characteristics of a foot orthosis which can have a direct influence on the foot's kinematics: it's coefficient of friction; it's surface geometry; it's stiffness. End of.. If only it were that simple?

    What we do know from finite element analysis is that if we take two devices with identical shell structure and add an external post to one of them, the one without the external post will deform more in the area of the talo-navicular joint than the one with the rearfoot post. I'm not saying that's a good or A BAD THING, but if it's all about controlling talo-navicular joint motion..
  11. David Wedemeyer

    David Wedemeyer Well-Known Member

    These MASS threads are like a train wreck Simon, the authorities keep saying "move along, nothing to see here" but you just gotta look!
  12. Simon:

    However, if the orthosis is made of a non-homogenous material with topcovers and forefoot extensions, then other factors such as topcover thickness and topcover/extension geometry/stiffness should be added to your list. I would also add that the sagittal plane angle of the orthosis relative to the weightbearing surface will directly affect foot kinematics/kinetics that may be independent of surface geomety, stiffness and coefficient of friction.
  13. And I think there is another element. If there is a medial flange then the device will deform medially under stress, especially if there is a significant transverse plane element to the probation. If the device has less of a medial flange, it will tend to flex downward. If it is deforming medially, then the stiffness of the shoe it is in becomes highly significant! The shank is not the only part of the shoe upon which an orthotic can be dependant.

    And of course one must consider that the pressure from a pronating foot is not distributed evenly across the insole as a bladder will exert. I suspect that this is significant also!
  14. Just realised I wrote kinematics above, I meant kinetics. Non-homogenous materials, top-covers and forefoot extensions can still only ever influences the devices geometry, stiffness and friction. I don't follow your last point Kevin, surely sagittal plane angle is an issue of surface geometry?
  15. But the device itself has still only altered the stiffness, surface geometry or friction at the foots interface. End of story.
  16. Simon:

    Once the geometry has been established within an individual foot orthosis, the function of that foot orthosis can then be altered by the heel height differential of the shoe, without affecting the overall shape of the orthosis. Therefore, I believe you must add "shoe geometry" to your list of "geometry, stiffness and friction" to be more complete and accurate.
  17. I think I see simons point. The heel height of the shoe is one of many external factors which will affect how the insole works, but it remains an external factor rather than a part of the nature of the insole itself.

    I'm still not 100% happy with the description though. I'm not sure stiffness covers it. An insole made of more than one material will not simply flex. The first element of resistance will be the compression of the softer material. That in turn will affect the distribution of pressure on the shell.
  18. In my mind that all relates to stiffness - maybe you can break stiffness down into sub components but it is still stiffness.
  19. Yeah, if we laminate two or more materials together we get a net stiffness for the materials. The shoe is an extrinsic factor, true. But it is the shoe not the orthosis which is different Take a patient standing in a shoe, we then add the orthotic to the shoe- what has the othotic changed? The orthosis can only change the surface geometry, stiffness or frictional properties at the foot's interface. I may have missed something, but I don't think so. With regard to pressure changes, pressure = force / area- the orthosis changes contact area due to alteration of surface geometry at the foots interface.
  20. From the viewpoint of the foot, I guess its all the same. Maybe load deformation is more accurate?

    I'm just thinking of, for Eg, an insole with 6mm poron over a 100% rigid shell. There will be a load deformation curve (No resistance, some resistance, 100% resistance) but the plate itself does not flex. Can, then, we still consider it in terms of stiffness? Stiffness to me suggests the ability of the unit to flex.
  21. Define stiffness.
  22. If we think of something else say car suspension I´m not real car guy but if I want to increase the stiffness of the suspension there is many components which I can change to increase the suspension stiffness. The spring, the shocks, the rubber bushel etc the overall suspension stiffness will have got stiffer.

    It does not really matter which of the changes has the greatest effect as we discuss overall the suspension.

    do you agree ?

    then the stiffness of the orthotic is the sum of the stiffness of the components which make up the device plastic, poron cover etc = Total stiffness.
  23. Define body.
  24. If we are thinking about orthotic stiffness, then in this instance the body is the orthosis.
  25. But the car is a solid mass exerted through a single (ok, 4) points. Whereas the foot is not.

    If the foot was homogenous, like the bladder, then yes I'd agree. the resistance posed to the foot could be considered as a composite. But its not, there will be peak pressures and such. A compressable material on the top will behave differently depending on the area, as well as the magnitude of force.

    So for EG. Let X be the amount of force needed to compress a piece of poron of 30 cmsqu to half its thickness (Y). If we consider the insole in its its entireity then X is the amount of force needed to get that degree of deformation in surface geometry.

    But the load is not distributed evenly. Lets say we are interested, in particular, in the height of the MLA. Lets further say, hypothetically, that when the foot pronates the peak pressure is sub navicular. How much force will be needed to get the navicular down by Y. Less than X I suggest.

    Good discussion!
  26. My point. Can we consider the orthoses as a whole? To borrow Mike's analogy, can we talk about the suspension of the car in general, or must we consider each of the wheels separately?
  27. Griff

    Griff Moderator

    What the hell are you guys playing at - this is a MASS thread, and you've hijacked it with proper science talk... shame on you ;)
  28. Who's considering it as a whole? Robert, think back to my FEA animations in Portugal, was the orthosis uniformly stiff across it's surface? Even with an homogenous material, and a uniformly distributed load, the stiffness of the orthosis will vary from point to point due to variation in the local geometry. I'm not saying the stiffness of an orthosis is the same under the medial tubercle of the calcaneus as it is under the base of the 1st metatarsal. I'm not saying that if we have variation in material components it won't also result in local variation in the orthosis stiffness. Hence my comments in post no. 10 of this thread; to reiterate: "we can inflate an air filled bladder on top of a device and then sand-blast the device so that it deforms a certain amount under the bladder's load, but this is not related to how the device will perform in-vivo because we don't know the loading pattern in-vivo. How much and where should a device deform?" But what I am saying is that mechanically the orthosis can only alter the stiffness, geometry or friction (under a given part of the foot, if that helps)- it's a shaped structure made of inert material(s), can you think of anything else it can do to influence the foots kinetics?
  29. I guess not. I do see what you are driving at, I'm just a little unsure about considering compressive resistance and flexion resistance in the same catagory.

    I suppose, playing devils advocate, that exteroception might be considered significant (or not), but then that would be a quality of geometry and friction wouldn't it.
  30. Hangs head in shame.

    Had to do something! Since no one is defending MASS....
  31. I'm not so certain just the term "orthosis stiffness" is the best term to use to describe the ability of all the parts of the orthosis to resist deformation in all diretions. Here we have a material with complex curves that may be deforming in multiple directions from the individual's foot at any instant during gait. Does "stiffness" apply to all the internal forces that resist deformations from the foot? Maybe, but it's not the best term in my opinion. The term stiffness would need to allow for multiple parts of the orthosis and multiple planes of deformation of the orthosis to also be included at any instant during gait.

    I believe that the term "three-dimensional load-deformation characteristics" which would be a much more inclusive and accurate term than simply using the term "stiffness" to describe the load-deformation characteristics of multiple parts of the orthosis in all three dimensions?

    Good discussion.:drinks
  32. I disagree. I believe stiffness is the correct term and is the term that is used in engineering to refer to the load / deformation characteristics of a structure (an orthotic is a structure). Stiffness relates not to just one degree of freedom and so encompasses the 3-dimensional load / deformation of any particular point within the orthotic.

  33. However, when you state that "orthosis stiffness" is one of the primary factors that determines orthosis function, are you referring to heel cup stiffness where each point along the curve of the heel cup may be bending in different directions at the same time, or are you referring to medial longitudinal arch stiffness, or lateral longitudinal arch stiffness or all the possible stiffnesses of the orthosis component parts that can be made on a single orthosis, in all different directions at any time during gait?

    Certainly using a term such as "stiffnesses" or "stiffness of orthosis components" makes much more sense from a biomechanical standpoint since "orthosis stiffness" to me, is a ambiguous term unless one first designates the point on the orthosis where the load is being applied and also designates the direction in which the loading force is being applied.

    What is your definition of orthosis stiffness?
  34. Graham

    Graham RIP

    You guys are such "Stiffs":drinks
  35. That's the key, there is no such thing as a single orthosis stiffness and for every given point on the superior surface of an orthosis (the area that is in contact with the foot) the stiffness will vary depending on the geometry and material properties of the device. You cannot talk in terms of one orthosis stiffness, but you can say that one of the three mechanical ways in which orthoses work might be to alter the stiffness characteristics at the foot's interface. Each point of the orthosis in contact with the foot will have a different load applied to it at any point in time during dynamic function and will deform in accordance with the physical laws which govern it behaviour under that load. That's why you need to run finite element models to get to grips with this.
  36. Here's a finite element plot showing the displacement under a uniform constant vertical load in a homogenous foot orthosis (polyprop). Hopefully, you can see that the deformation is not uniform across the surface of the device (different colours = different deformation) Stiffness = load / displacement, load was constant. I've got tons of these showing what different design features do to the stresses and displacements within the devices, but they're .avi files so I've just quickly screen grabbed a still from one.

    Attached Files:

  37. Here's another one, same basic shell but without a rearfoot post, note the difference in the areas of relative stiffness in the superior surface of the device between this and the previous image.

    Attached Files:

  38. Yes, and stiffness too. I'm not talking about what the foot brings to the party, only what the orthosis adds mechanically to alter the kinetics of the foot. Hopefully Kevin and I will get this paper finished soon.
  39. yeah, check out the load/ deformation on this face...

    Attached Files:

  40. Someone should split off this excellent discussion on orthosis stiffness out of this "MASS" (whatever that acronym means currently) thread.

Share This Page