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Formthotics; Do you need the heating machine?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by footsteps2, Jul 19, 2011.

  1. footsteps2

    footsteps2 Active Member

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    Has anyone used the Formthotics with or without the heating machine? Can a heat gun be used instead or is the heating machine a necessity?
    Do the Formthotics have to be in shoe when heated on the machine?

    Where I work part time (employed) they are thinking of using the Formthotics and just want to know best way to heat them before moulding to the foot.
  2. Paul Baalham

    Paul Baalham Member


    I use Formthotics and you do not need to use a heating machine to mould them. I find that a heating gun is adequate for the task.

    The heating machine is designed for heating the formthotic in a shoe. With a heating gun I dont think it a matters if you heat them in or out of the shoe.


    a heat gun is all you need.

    Turn the heat down and take your time, heat in the shoe but be careful you can melt the shoe.
  4. Craig Payne

    Craig Payne Moderator


    I know Charlie hates it when I say this, BUT you can not heat mold a shank dependent EVA/PE prefabricated orthoses.

    and Simon and I said you can change the stiffness of a device by changing the shape, but we never heard back from you ;)

    ie if you increase the arch shape of the formthotic you have changed the stiffness of the device.

    if this change in stiffness is significant is a whole other story
  6. Craig Payne

    Craig Payne Moderator


    Sorry, I must have missed that.

    BUT, how do you change the arch shape of a Formthotic or any prefab by heating it? As they are shank dependent, as soon as you stand on the device, the shape is determined by the thickness of the material and there is no way that heating changes the thickness of the material.

    If you do not believe me, get some calipers and measure the thickness of the prefab in a few locations; heat them following the manufacturers instructions, then measure the thickness of the material in the same spots again. Did it change?

    You can heat and bend a prefab and let it cool down and it will maintain that shape, but as soon as you stand on it its shape is determined by thickness; heating does not change that thickness; - the only way you can change the shape is by gluing bits on or grinding bits off.

    I can't believe people fall for this (and worse, that people can keep a straight face when the teach this).

    (Disclaimer: There probably is some benefit to heating the heel area of a Formthotic to facilitate its initial fit into the shoe)
  7. Boots n all

    Boots n all Well-Known Member


    Craig l am suprized you took so long to reply to that one;).

    Heating in the shoe? brave people, if it gets hot enough to make EVA mouldable:confused: the heel stiffener would also become soft......mind the synthetic linings and the Velcro which both melt at low temps
  8. phil

    phil Active Member


    I too have been very confused for a very long time about why I am bothering to heat these things up!

    Iv'e concluded it must be for a bit of theatrics, or maybe to make them feel nice and warm?

    Acutally, i think its so it takes a bit longer than 46 seconds, which it the resonable time it should take someone to remove the sock liners from a pair of runners and replace them with formthotics.

    Because, once you've stood on the things, they're gunna hit the floor no matter what temperature they are. Unless they're molten lava temperature, but then you've got a whole other bunch of problems on your hands.
  9. Craig Payne

    Craig Payne Moderator


    BUT, as soon as you stand on it, its back to its original shape. if there is a change in stiffness, then its going to be:

    Well, you can, but as you and Phil say its futile if that is ALL you do to it. You will change the shape and perhaps even the LD characteristics (a tiney tiney bit) but if you create a void under the inferior surface of the orthotic by raising the arch, the orthotic will change back to its initial shape under the slightest load.

    And I'd agree that the heating system with formthotics is nowhere near enough to heat the orthotic to the point of malleability all the way through.

    Heat moulding shank dependant pre fabs is one of my favourite ways to customise a pre fab, but you have to either add more material or grind some away from the underside of the device to make it practical.

    the whole potato potato thing - but then the question becomes what level of stiffness is required of the original device before bending will have a significant effect - but then I guess its all to do with supination resistance and other kinetic questions
  12. Craig Payne

    Craig Payne Moderator


    I have no problem with that and do it a lot.
    Take any of the EVA/PE prefabs (eg Formthotics; ICB; Vasyli; TaylorMade; etc); heat it; bend it with your hands; hold it there until cooled; place on flat surface ..... you can flatten it to its original shape with your little finger --> imagine what body weight does....

    Just done this, will upload photos later...
  14. Ok, here we go. So lets say we know that foot orthoses work by altering the magnitude, distribution and timing of reaction forces acting on the foot. And that we agree that basically they do this by altering the geometry, load/deformation and frictional characteristics at the foot-orthosis interface. In order for heat molding of eva devices to not alter the magnitude, distribution and timing of reaction forces acting the foot, then the heat molding cannot change the geometry, load/deformation and frictional characteristics at the foot orthosis interface. If it does then the reaction forces will be altered.

    So, quick bench test. I started with a block of 10mm thick eva and then did some work on a prefab. If anyone here believes that the heat molding of these has not altered the geometry or load/deformation characteristics, please speak now.

    Attached Files:

  15. Loaded upside down, turn your screen over, it'll be quicker than me fannying about with the pictures;)

    Here's where I think people are getting confused. Lets say we take two different devices of different shapes and different load/deformation characteristics. Lets say that during loading, equilibrium between the foot and both the orthoses occur such that the two orthoses are exactly the same shape at the point of equilibrium. Will the reaction forces between the foot and the two devices have been identical from the time of initial contact to the time to equilibrium?

    The answer you are looking for is no. So even if it does deform back to it's initial shape, the timing magnitude and distribution of reaction forces acting on the foot will have been altered. And since this is how foot orthoses work, we must have changed the way the orthosis works by heat molding it. I hope that helps.
  17. mgrig

    mgrig Active Member

    How significant could these changes be? the higher arch will make the device more rigid, how much is the question? Most likely You could deform the shape with you little finger, clinically significant? I doubt it.

    Perhaps the next test could be to measure arch deformation when placed under a various loads?

    I think if you are going to modify the arch height by heating, you need to then fill it with Eva.
  18. Yeah, so you've changed the geometry and the load/deformation characteristics....so the orthotic is going to function differently.:bang:
  19. RobinP

    RobinP Well-Known Member

    Good examples and pictures Simon

    What helped me to get a handle on this was the fact that it was not just the lowering of the arch of the prefab that was possible, but also the raising of the arch of the prefab. Raising the arch increases the stiffness and will have effects on fricition and thus change the magnitude of the forces.

    Yes, it can be pushed out by the amount of force from one's little finger. Does that make it clinically insignificant - not in my book.

    We have all seen patients with bits of cardboard in their shoes that have been enough to alter the forces enough to reduce tissue stress. Why shouldn't the miniscule change in surface geometry of a prefab be capable of doing the same thing?

  20. Thanks Robin,

    You've really got to go back to understanding how reaction forces are generated and the factors that influence them. Rate of transfer of momentum is good place to start.

    As you know the example I have used is two cars travelling at the same speed, one applies the brakes gently over a longer distance, the other slams the brakes on at the last second. Both cars stop at the same point on the road. But the braking forces (orthotic reaction forces) have been very different. This is effectively what changing the load/ deformation characteristics of the orthoses does.

    To better understand how altering interface geometry influences reaction forces, anyone interested should take a look at the paper which Dave Smith, Kevin Kirby and I wrote on in-shoe pressure measurement. I'm told it's helped a few people to get their heads around the influence of orthoses geometry and force vectors.
  21. One must also understand that in any discussion of both shank dependent and shank dependent orthoses, the orthosis will be signficantly influenced by its contact with the medial upper of the shoe. Just yesterday I had a patient that said that the orthosis felt too high in the medial arch when the orthosis was inside the shoe, but didn't feel too high when the orthosis was laying on the floor, without any shoe mechanical interaction. I simply narrowed the orthosis by 2 mm and he felt the orthosis felt much less high in the arch (the orthosis was sitting flat on the insole of the shoe both before and after adjusting the orthosis).

    I agree with Simon on this one....even the simplest flat flexible insole, when now placed into a laced up shoe, can have a signficant affect on foot comfort and foot function since it doesn't necessarily retain its flat shape when it lies against the medial upper of the shoe. These considerations are extremely important when we are discussing orthosis function, orthosis stiffness and orthosis comfort.
  22. If memory serves, Josh Burns did some testing on the "sham" devices he used in his PhD, these were very compliant indeed and similar to those used in the Landorf study. As I recall, Josh stated that these so called "sham" orthoses reduced peak pressure by about 10%.

    I challenge you. The first picture is the original shape of the eva (it's a slab here, but it could be part of a shank dependent prefabricated orthosis). I heated it up, bent it with my hands and placed it on a flat surface (second picture). Now, flatten it to the original shape with your little finger... go ahead, make my day. http://www.youtube.com/watch?v=gD3cYh5Pp1I. You can't get there from here. Y'all got to remember you can compress the device too when you heat-mold it... Have I changed the surface geometry? Have I changed the load/deformation characteristics? Is the pope a catholic? Does he wear a silly hat? Does he live in a council flat? OK, the last question might result in a negative answer, but these are the opening lines to the first song what I ever wrote. It was a deep mother about how completely out of touch religious leaders were with the "real" world at the time... I was about 17 at the time, glad to see how the world has moved on in the last twenty something years. Not. Of course, the pope is now an ex-member of the Hitler youth.... so all is well with the world, start singing... http://www.youtube.com/watch?v=rf6-5-9efM8

    "rivers rise as the rain descends, don't make that same mistake"- wise words.

    Attached Files:

  24. CraigT

    CraigT Well-Known Member

    Ha- just last week had a guy in who had 'orthoses' which were pieces of cardboard in his shoe. What was really interesting was that he had them since about 1993 and was a 'pretty serious' runner... How serious? Well he ran in the 10000m in 2 Olympics!
  25. Yeah, Eddie "the Eagle" Edwards represented the UK in a winter olympics http://en.wikipedia.org/wiki/Eddie_"The_Eagle"_Edwards. He was the best we'd got or have had at the event since. By olympic standards he was rubbish. How does Australia get on in international ski-jumping?

    Who was that olympic swimmer who swam about as quick as I did when I was 9 years old, who was at the olympics not too long ago?

    Viz. If I lived on the Isle of Man, I could probably be competing in the next olympic 10,000m, if the funding was available.
  26. RobinP

    RobinP Well-Known Member

    Against our Three Legged Marvels, I think not!
  27. Griff

    Griff Moderator

    Eric the Eel.

    Last edited by a moderator: Sep 22, 2016
  28. RobinP

    RobinP Well-Known Member

    Eric the Eel. I'd forgotten just how funny that was. AWWWEESSOMME!
  29. CraigT

    CraigT Well-Known Member

    Actually Simon, this guy has a sub 28 minute PB, so was the real deal. A lot slower now, but competed in the 92 and 96 Olympics...

    As for Australia at the winter Olympics, we would probably be just as crap as great Britain at ski jumping, but we have a few medals. Most infamously is our first gold-
    I remember listening to a US commentator saying 'that will be the first and last gold medal for australia at the winter olympics'... then we won another the next day in aerials...:D
    Last edited: Jul 20, 2011
  30. Maybe you can bring back the GB tradition in Ice Hockey Simon

    GB have a Gold and a Bronze even beat Canada to win the Gold.
  31. Bone

    Bone Member

    I would agree that you don't need the heat machine, however you will get a much better heel cup shape, arch contour and even heat distribution if you use the formthotics heat machine.

    The downside of using a heat gun is time wastage, accidental burning of the shoe, particularly the fabric around the heel counter or nylon mesh within the shoe, and spot overheating of the formthotic, and uneven heating of the formthotics.

    I have worked in a number of clinics with high volume formthotic use, by far the best result and use of my time was the clinic with the heat machine, for forming and subsequent modification of formthotic bulk and prescription angular changes (posting) for the device to encourage positive change in foot mechanics.

    Heat gun or machine you will get better results with in-shoe heating.

    These days I prefer the accuracy of a good lab.
  32. Craig Payne

    Craig Payne Moderator

    Simon - I will get my own pictures in response soon..
    How? How do you actually change the arch contour if heating does not change the thickness of the material?
  33. Bone

    Bone Member

    Grinding and heating.
    I agree with you Craig, there are way too many variables with pre-fabs.
  34. Craig Payne

    Craig Payne Moderator


    OK, here is my photo. This was a prefab that I heated with a heat gun and bent in the arch and let cool down. As you can see with next to no effort from one of the Arena'ettes, were able to flatten it with her fingers -- that hardly represents much if any change in stiffness, esp if it was a foot and bodyweight doing it.

    Attached Files:

  35. Boots n all

    Boots n all Well-Known Member

    Simon, out of curiosity what was the density/hardness of the EVA you compressed so easily?

    Lower density materials will compress easier and stay that way compared to the higher density materials.

    Remember these Pre fabs are ranging in the 4mm-5mm thick in hard EVA's, the percentage of compression available is less in the higher density materials.
  36. Shore 50. A low density vasyli prefab is shore 45, medium density Vasyli is shore 55. Next...
  37. ........Next, I took a commercially available prefab and put it into a materials testing machine (see the picture) 15mm flat disc probe, I added two restraints as seen and measured the height of a point in the medial longitudinal arch section and proceeded to plot load/ deformation data.

    Then, I heat molded the device by hand and increased the arch height and repeated the process of measuring load/ deformation

    Then, I heated up the device again, this time lowering the arch and repeated once more.

    The load/ deformation curves are attached in the .pdf.

    The unloaded height of the arch in the unmolded state was: 23.93mm
    The unloaded height of the arch after the elevation/ heightening molding was 29.93mm
    The unloaded height of the arch after the lowering molding was 18.83mm

    Loading was increased on the device such that 1mm increments of deformation were observed. Thus, given that the height of the elevated molding was 6mm higher than the unmolded state, 6mm of deformation and the load required to achieve this should be necessary to bring the height of the arch to the same level that it was at prior to molding (roughly).

    So, one way to view this data is to look at the graph, and compare the load at 7mm deformation for the heightened molding and compare that to the load of the unmolded device at 1mm deformation since the device should be roughly the same arch height at this point (Craig's contention that the device returns to the same shape under loading- right?). In other words, in order for the area of the foot which interfaces with this area of the orthosis to occupy the same point in space on the two devices, this area of the foot would need to apply a force of 36N on the device with the heightened arch, but only 10N on the unmolded device. Remember Newtons 3rd law: if the foot is applying a load of 36N to the orthosis, the orthosis is applying a load of 36N to the foot; if the foot is applying a load of 10N to the orthosis, the orthosis is applying a load of 10N to the foot over this area. Thus, the orthosis with heightened arch applies 3.6 times more load to this area of the foot at this point in space compared to the unmolded device.

    A simplified example of the potential significance of this difference: lets pretend that this force is the only reactive force at the foot-orthosis interface, lets assume a vertical force vector, lets assume the centre of pressure of this force is 10mm from the subtalar joint axis. Moment = force x distance

    36N x 10mm = 360Nmm
    10N x 10mm = 100Nmm

    It's a bit rough and ready, but hey: what did you do between patients today?

    Attached Files:

  38. RobinP

    RobinP Well-Known Member

    I read Kevin's article on "Precise naming aids dorsiflexion stiffness diagnosis"

    only slightly less geeky!

    Good graph - curious as to why the raised arch showed lower load for the same deformation relative to the others as the deformation increased
    Last edited: Jul 21, 2011
  39. I think it was the restraints I used. With higher deformations the prefab tries to lift off on the lateral border so it's probably error related to this.

    N.B. this was really just a quick show and tell. A bit of scratch "n" sniff science.:drinks it is obvious though that heat-molding of prefabs is capable of changing both the surface geometry and load/deformation characteristics of prefabricated devices. Thus the timing, location and magnitude of the reaction forces occurring at the foot-orthosis interface can be changed by the heat-molding process. QED

    Whether or not these changes are clinically significant is another story.

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