Ed!
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Ed!
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
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Ed!
Please! It would be helpful if you could give these questions some thought.
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Please! It would be helpful if you could give these questions some thought.
Ed,
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?
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Please! It would be helpful if you could give these questions some thought.
Ed,
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?
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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 -
Ed Glasser Accepts defeat?
Ed,
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? -
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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... -
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. -
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.. -
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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. -
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! -
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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. -
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. -
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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. -
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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. -
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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! -
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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. -
Had to do something! Since no one is defending MASS.... -
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 -
http://en.wikipedia.org/wiki/Stiffness -
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? -
You guys are such "Stiffs":drinks
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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:
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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:
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Attached Files:
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Someone should split off this excellent discussion on orthosis stiffness out of this "MASS" (whatever that acronym means currently) thread.
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