REDUCING FOREFOOT CRASH SPACE


In my post, TONGUE SURGERY, I described how the tongue in my Head World Cup boot was blocking the glide path of my ankle joint by introducing an unwanted source of resistance at the lower end of my shank. By removing all the foam in the tongue below the lower end of the force distribution zone and adding a rectangular layer of foam directly in front of my shin bone, behind the existing layer of chip foam, I increased the space between the plastic tongue body and the lower end of my shank. But I also want to reduce the rearward movement at the transition of the tongue body that occurs when the tongue is bent in dorsiflexion.  I achieve this by trimming the sides of the tongue body as shown in the photo below.

Tongue trim 2

The red dashed lines show where I trimmed the sides of the tongue body and enlarged the neck at the narrowest point. Here’s a side view.

Tongue trim 1

I leave the fabric-foam outer skin run wild instead of trimming it to the shape of the tongue. The reason I do this is to lessen the tendency of the edges of the tongue to snag on my sock when I insert my foot into the boot. I also don’t re-sew the fabric-foam to the tongue body or glue it in place. Both these can stiffen the tongue at the transition bend. Putting my boot on can be a bit tricky a first. I place the tongue on my shin with my forefoot in the shaft. Then I grasp the boot shaft and shove my foot in. Once my foot is in the boot I wiggle the tongue to make sure it is in the right place.

To reduce the crash space over my forefoot I make a new foam pad to replace the original chip foam pad. I start off making the pad bigger than it will eventually be then trim it down as necessary to enable me to get my boot on.  Here is what the foam forefoot pad for my boot looks like.

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I usually taper the top edges to give the tongue a shape that won’t conflict with the shape of the boot shell above. I secure the pad in place with 2-sided tape instead of gluing it. This makes it easy to reposition the pad or remove and replace it. I fold back the fabric-foam skin,  stick the foam pad to the underside of the tongue body then fold over the fabric-foam skin.

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I try foams of different densities and resistance to deformation to try and find the one that works best. When I did a lot of boot work I acquired such a good supply of foams that I have not bought any in years. So I can’t recall the types or sources I am using. But here’s a photo that shows half of the original chip foam tongue alongside some samples from my stock of foams.

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Here’s what the front of the tongue looks like with the foam pad in place. Note the gap behind the forefoot pad in the transition bend that allows the tongue to bend independently of the foam-fabric skin.

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In terms of reducing the crash space, I just want to take up any space between the top of the high point of my foot and the boot shell while leaving space at the back end for the glide path of my ankle joint. I don’t want to feel a significant force pressing down hard on top of my foot.  If the pad is not quite thick enough to fill the space, I add a thin layer (2-3 mm) of dense foam that compresses very little. The net ramp angle of 3 degrees in combination with 14 or 15 degrees of lead segment ankle flexion turns on the stretch reflex in my legs. The stretch reflex enables my balance system to maintain the position of my CoM over my feet on what Ken Chaddock (Ski Simply Well) calls the Magic Carpet. The stretch reflex also allows my muscles to absorb energy from perturbations in snow reaction force that would tend to disturb my equilibrium. This gives me the best ride for the least effort.

In my next post I will discuss joint angles of the legs and pelvis,

2 comments

  1. I’m surprised the purple foam pad isn’t a little more wedge shaped…tapered forward. My memory of the birdcage boot was that its main restraint was the foam pad just forward of the instep, and that its function was to restrain the upward motion of the instep, but also to force the entire foot back to seat the heel in a relatively immobilized position…hence the wedge shape.

    1. You will see this wedge shape in the tongue system that I made for my wife’s Head boots. At some point I will do a post that compares her boots to mine. It involved major work. The issue I have to contend with is getting my US men’s size 12 foot into the very stiff Head shell. I can’t spread the sides of the forefoot of the boot very much. So I had to find the best compromise. Interestingly, as long as I have a reasonable load on my instep and I maintain COP in front of the base of my shank and behind the balls of my feet with the muscles in the back of my legs in eccentric contraction, I can absorb energy from perturbations in snow reaction force without getting thrown around whereas in a boot that disrupts the physiology of my ankle joint I would be tossed all over the place. It is hard to appreciate what I am experiencing until one gets everything right in the equipment system. Then the whole world seems to change. When this happens skiing suddenly becomes effortless.

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