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Here you go Craig, here is an analysis of the variation in normal force components on the surface of a foot orthosis that I did for our paper on in-shoe pressure measurement. In the analysis each point on the orthosis surface was loaded vertically with the same force, say 10N. The magnitude of the normal component of the force at each point on the orthosis is proportional to the length of the green arrow, so too will be the magnitude of the shear components (parallel to the orthosis surface at each point). So, the shorter the normal component, the bigger the shear component and vice versa. You could do the same thing with your heel cups.
Re: Will increasing the friction of the topcover increase the supination resistance of the foot? And if so, how and why?
Quote:
Originally Posted by CraigT
Hi Simon
I will have a closer look at this in a couple of weeks... packing for a weeks holiday at the moment... but a quick observation-
Aren't the shear components going to be in the opposite direction on the lateral heel cup??
Opposite direction to what? To the shear components on the medial heel cup, yes. Where did I say they wouldn't be? Enjoy your holiday.
Re: Will increasing the friction of the topcover increase the supination resistance of the foot? And if so, how and why?
[quote]Originally Posted by CraigT
Hi Simon
I will have a closer look at this in a couple of weeks... packing for a weeks holiday at the moment... but a quick observation-
Aren't the shear components going to be in the opposite direction on the lateral heel cup??
Opposite direction to what? To the shear components on the medial heel cup, yes. Where did I say they wouldn't be? Enjoy your holiday./QUOTE]
I wasn't happy with that my comment of mine and I deleted it... bloody hell you are quick!
To be continued....
__________________
Craig Tanner
Podiatrist ASPETAR-
Qatar Orthopaedic and Sports Medicine Hospital
Doha
QATAR http://www.aspetar.com/
Re: Will increasing the friction of the topcover increase the supination resistance of the foot? And if so, how and why?
Quote:
Originally Posted by Kevin Kirby
Why do you think that anything I said here makes you assumes the foot that I think the foot is not a deformable body?
Because you appeared to be suggesting that shoes could prevent slippage of the section of the foot in contact with say, point A on the orthosis surface such that it wouldn't tend to slide toward the section of the foot which interfaced with point B on the orthosis surface even when the surface angulation at point A exceeded the angle of friction between the foot and orthosis at this point and when the surface angulation at point B did not exceed the angle of friction between the foot and the orthosis. This might be the case if the foot were a rigid body, but not in reality because the foot is a deformable body. How do shoes prevent this occurring in the presence of a "deformable" foot?
Here's what happens when you have a deformable object (let the car = foot) sliding into an immoveable buttress (lets say the wall here is the lateral heel-cup of an orthosis + the shoe): http://www.youtube.com/watch?v=gPsRb...eature=related See how the wall (lateral heel cup) prevents the car (foot) deforming with it's wheels not sliding toward the buttress and instead arrests the motion dead without deformation. Not. Indeed, does the wall/ buttress/ heel cup/ lateral shoe improve this problem or actually make it worse? That'll be worse then. The solution might be to increase the co-efficient of friction between the wheels (foot) and the road (orthosis) so the car (foot) doesn't slide into the wall (lateral heel -cup + shoe) in the first place. But if sliding (shearing) doesn't occur at the orthosis-sock interface nor at the sock-foot interface it will occur within the subcutaneous tissues and the underlying osseous tissues. This could be good if you want to change the forces acting upon the underlying osseous tissues, but not so good if the shearing is so excessive that it creates pathology. Yet, that's only if you believe that the frictional characteristics at the foot orthosis interface are important.
Re: Will increasing the friction of the topcover increase the supination resistance of the foot? And if so, how and why?
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