Liners

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.

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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.

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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,

TONGUE SURGERY

In my post, TONGUE TIED, I described how a conventional ski boot tongue can block the glide path of the ankle during dorsiflexion, disrupting the physiology of the ankle joint. It is essential to avoid this especially in dynamic activities such as skiing because the ankle joint is a portal for the flow of neural information. Neural flow from the more than 200,000 nerve endings in each foot and mechanoreceptors in the ankle send a flow of proprioceptive, sensory information to the central nervous system where it is processed and used to generate postural responses that sustain balance. Disrupting the physiology of the ankle joint with physical structures can disrupt neural flow and introduce foreign forces into the ankle joint that contaminate neural information from mechanoreceptors. Disrupting the physiology of the ankle joint has a similar effect on the balance system as  taking a hammer to your computer or smart phone then expecting it to still work.

My US Patent No. 4,544,299, published almost 30 years ago, discloses an in-boot tongue fit system that restrains the foot without obstructing the glide path of the ankle joint. The short video clip below shows a section through the center of the tongue system superimposed over the actual patent figures to illustrate how this system works when used in a conventional ski boot shell. The shank and forefoot portions are separate components joined by a flexible link. This allows the components to maintain their respective positions on the shank and forefoot during ankle flexion.

The in-boot system allows the ankle to flex while maintaining the position of the load centre on the shank. In order to keep the load on my shin centred in my Head World Cup boot work I had to perform some tongue surgery. The photo below is of the original tongue sectioned through the centre to reveal the core.

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The first thing to note is the use of chip foam for the tongue padding. Chip foam is made from foam scraps that are ground up and held together in matrix with a bonding agent. It has been my experience that chip foam has very poor energy absorbing qualities. My first procedure will be a partial chip foamectomy. Since I only want the lower distribution of force on my shin to extend a little further below the load centre at the top of the front of the shaft than it extends above the load centre I don’t need any foam below this point where it could load my shin. I am also going to surgically remove a portion of the outer padded tongue skin since it is folded over adding thickness  in the glide path of the ankle, the very place where I don’t want any foam or padding. While I am at it, I am  going to remove all the chip foam from the forefoot of the tongue since it is next to useless anyway.

Here’s what the tongue looks like after removal of the foam.

Post foam re

In addition to removing the foam, I also trimmed off the front of the plastic tongue body that would normally be used to stitch the tongue to the liner. I want my tongue to be able to ‘float’ in the forefoot area to reduce any possibility of the transition blocking the glide path of my ankle joint. As my shin approaches the front of the boot cuff in the lead segment of flexion, I want to decelerate the movement as opposed to having my shin slam into the top edge of the shaft (aka Lange Bang). I also want to create more space below the pressure distribution zone to help maintain the centre of pressure while reducing the possibility of any load at the bottom of my shin that could block the glide path of my ankle. The solution? Add a band of foam to the tongue in front of my shin bone as shown in the photo below.

Foam add

I don’t want to add foam to the entire area of the tongue. I only want to add a rectangular band of foam that is directly in front of my shin bone. The reason for this is that there is usually a gap where the sides of the liner overlap the sides of the tongue. Placing a band of foam in front of the shin bone draws the sides of the tongue inward as my shin pushes through the gap. This assists the deceleration of the forward movement of my shin during ankle dorsiflexion while helping keep the force centred. The photo below shows the gap.

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When I am skiing, the only time I would ever have any perception of contact of my shin with the front of my cuff is if I were to get momentarily pitched forward. Even then, any sensation of any contact is minimal. When I am skiing, the only sensation I am consciously aware of is the considerable tension in the soles of my feet.

In my next post I will discuss final tongue modifications including how I reduce the crash space over my forefoot.

 

BOOT FLEX CAN BE A REAL TURN OFF

The title refers to the ability of the shaft of a ski boot to disrupt and contaminate the neuromuscular processes of balance and, in particular, to diminish or extinguish the contraction of muscles that would normally act to oppose forces that tend to disturb balance. As a prelude to discussing the measures that I use in my ski boots to mitigate these effects I will address the widespread perception among ski professionals and coaches that the ski boot does not signficantly affect skier performance.

Although the design of the modern rigid plastic ski boot has some serious shortcomings, the fact of the matter is that some skiers can ski reasonably well in these boots. It is also a fact that many World Cup and Olympic medals have been won on them. This has spawned the erroneous assumption that if a skier is having problems with their skiing skills the problem lies with them, not their equipment and especially not their ski boots. The reasoning of many ski professionals and coaches is that if they can  ski without apparent difficulty in stock ski boots then acquiring skill in skiing is a simple matter of technical training and practice.  Unless one regressed, as I did after switching from low-cut leather boots in which I was an expert skier to higher, rigid plastic boots in which I was reduced to the level of a beginner, they would not have the benefit of the perspective of the ski boot as the problem. Further, until one gets very close to the optimal ski boot configuration any interference with the function of the feet and lower limbs, in particular the processes of balance, caused by the ski boot is unlikely to be perceived.

My experience with my spouses’ ski boots serves an example of how fine the line is that separates performance from dysfunction. This season I made what I thought were minor changes to her boots. But these minor changes had negative effects on her skiing far in excess of anything I could have expected. I replaced the soft fabric Lange liners in her 10 year old Head boot shells with identical new Lange liners. The reason for this change was that the old liners were disintegrating. I removed the stock Lange tongue from the new liners so she could use the tongue fit system from her old liners. But I did not cut away the seams along the sides in the front of her liner as I had done with her old liners. The reason I do this is to ensure that the metatarsals can spread under load. One significant change that I did make was to use a stock Lange insole in place of the much thinner insole in her old liners. The special tongue fit system I invented in her boots is the principal fit component. This did not change.

What happened on snow was startling.  In the first few meters of her first run my spouse went from an expert to a struggling beginner. She appeared to have little balance or control. She told me her boots felt completely wrong and that she was disoriented and could not find her balance. Her situation was so bad that we left the ski hill after one run and went home to assess the situation. After we got home I cut away most of the front of her liners. I also heated the Lange insoles and pressed them dead flat because she complained they were digging into her arch. This seemed incredible to me because the Lange insoles have almost no arch form.

The photos below show the new unmodified Lange liner on the left with the same liner modified after her skiing experience on the right. I left a small amount of the toe box of the liner to help keep the insole from creeping forward. On the left liner I also cut away some of the plastic backing of the cuff to allow her calf muscle to sit properly.

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When we went back on the ski hill the change in her skiing was dramatic and instantaneous. A similar thing happened to me with interference with the arch of my left foot. When I am in a moderate to high speed GS turn the tension in the sole  of my outside foot is so great that it feels as if my foot is made of steel and the base of support on my ski feels as if I am standing on a concrete surface. With this amount of tension anything that impinges on my arch feels like a sharp stone in my shoe. I had an interference problem in the arch of my left foot that was not addressed by shaving down an already flat insole. I eventually traced the problem to the detail of the sole of the liner that rises up along the inner aspect. Cutting away this section of the sole resolved the problem. The photo below shows the portion of the liner that was causing the problem.

Arch int

The ability of the ski boot to significantly affect skier performance was described in The Shoe in Sport 1989 – Published in Germany in 1987 as Der Schuh im Sport. ISNB 0-8151-7814-X (27 years ago). Despite the call by scientists for a ski boot based on a design that from a functional point of view that takes into consideration the realities of functional anatomy (axes etc.) a significant component of the design of ski equipment and the formulation of ski teaching and coaching methodologies continues to be influenced by opinion and subjective observation. Ski pros and coaches tend to interpret what they see in the context of what they know or what they believe they know. Although athletic prowess is arguably a factor, a significant but unrecognized factor confounding the analysis of technical faults is that the ski boot acts as a selective filter that literally determines how well someone can ski based on the physical characteristics of their feet and legs. Those who are able to ski with reasonable efficiency within the constraints of a ski boot become ski instructors. Those who ski really well become racers. The remainder languish as terminal intermediates. Levels of competition act as selective filters that eliminate those more compromised by the constraints imposed by their ski boots. Ski pros and coaches tend to view their charges based on a paradigm in which the ski boot has no effect on skier performance. Even today some coaches continue to argue that the in-boot technology that I invented and that Podborski used to compete and win on a partially healed knee was not a factor in this success, that it was training or some other factor.

A  book that I just finished reading, one  that substantiates my position that with rare exceptions ski teaching methods tend to overlook the effect of the boot on the skier, is Ski Simply Well by Ken Chaddock (http://www.skiwellsimply.com/). Chaddock is a local Ski Pro who teaches on Whistler-Blackcomb. With the exception of a few omissions, Ski Well Simply is simply one of the best books I have ever read on ski teaching, bar none. But while Chaddock raises the issue of cuff cant angle which is important, he appears to make the common assumption that those who read his book will be able to ski the same way he does. What Chaddock gets right, and he really gets it right, is his description of how he develops plantar tension in the soles of his feet and skis with minimal use of the cuff of the boot. Chaddock gets so much right that in a future post I will fill in the missing pieces and connect the dots he missed.

In my next post I will describe how I build a tongue that lets me ski in a minimal boot shell.

 

 

 

 

LINERS – HOW MUCH IS ENOUGH?

After you read my posts on foot and leg shape, ramp angle and what I look for in a ski boot you may have concluded that all you have to do is get the boot shell right, insert the liners and go skiing. Not quite. It is a little more complicated than that. In my experience, ski boot liners, especially custom-fit liners, can cause more problems than almost any other piece of ski equipment. “Seriously”, you say. “How is that possible? I thought boot liners were designed to help me ski better”. Maybe that was the intent. But I have yet to come across an explanation based on sound principles of science, let alone research that will withstand rigorous scrutiny, that supports the concept of attempting to immobilize the foot and leg within what amounts to an orthopaedic splint. If anyone knows of such an explanation and/or studies please let me know.

If you are like most skiers, you are probably reluctant to do anything significant to the liners of your boots, let alone do anything radical. It is reasonable to assume that if the manufacturer made the liner a certain it was probably for a good reason. There are several reasons I can think of that might explain why liners are made the way they are. But they have to do with manufacturing considerations, not skier performance.  The question is how much liner do I need to ski well? In Steve Podborski’s case, the question is how much liner did he need to ski not just well, but well enough to become the only non-European to win the World Cup Downhill title? The answer will probably surprise you. And let’s not forget that in the 1980-81 World Cup season where he almost won the downhill title he wasn’t even supposed to be skiing because he had torn his ACL 4 months before the start of the first race.

The photo below is of a stock soft-fabric Lange liner similar to the ones I built boots with in 1978-79.

Lange liner

The photo below is of the liner that Steve Podborski used in the ski boots that he wore when he almost won the World Cup Downhill title in 1980-81 and in the 1981-82 World Cup season when he won the the title. The liner is a little worse for wear because he skied in it from the start of the 1980-81 World Cup season until he retired.

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Two cap screws on the back of the moulded plastic spoiler of the liner secured it to the top of the boot shell cuff.

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The series of photos below are of the liner from the Head World Cup boot I am currently skiing in. The first photo is of the inner aspect of the right liner. The cutout below the cuff creates clearance for my inside ankle bone to move towards the shell wall as my foot pronates. The outer layer of the liner beside the ball of my foot has been cut away to allow the side of the ball of my foot to sit against the shell wall. The entire front portion of the liner has been removed to allow my foot to spread and elongate under load.

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This is the outer aspect of my right liner. The portion of the liner adjacent to my 5th metatarsal has been cut away to allow my foot to spread under load as it pronates.

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Top view of the right liner with no insole in place.

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Top view of the same liner with a Superfeet insole in place that I heated, put in a press and compressed it until it was dead flat.

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Bottom view of my liner. I intentionally purchased an insole that was too big then trimmed it to the exact length and shape of the base of my boot shell. Note how it slightly overhangs the front of the liner and especially how it overlaps the outer aspect of the sole of the liner.

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In my next post I will talk about how the tongue configuration I use makes a liner like this work.