Ski boot modification posts


“A problem with stronger sports people is that they can ‘fake’ the outcome. But when it comes to free form, fluid skiing… the real deal is still missing (for me).” – Whistler Ski Pro, Matt

Since last fall, I have been working with Matt. His situation is not uncommon. It is one thing to look like a good skier. It is another matter entirely to be able spread your wings and fly like a bird in free form, fluid skiing. A small number of skiers can ski at this elite level in boots right out of the box, with little or no modification. These are the skiers that rise to the top. Based on my experience, I estimate that this elite skier group makes up less than 0.5% of the skier population. But these are the skiers those such as Matt are chasing but never getting any closer to, no matter how hard they work at their skiing. Matt’s problem isn’t a lack of talent, fitness or athletic ability. Matt’s feet are simply out of specification for most performance ski boots.

The reason I started this blog is to provide serious skiers like Matt with information that would help them realize their full potential. About a year ago, I started working with a small number of serious skiers and racers in different parts of the world, mostly by email. Since that time, I have learned a lot more than I previously knew about how equipment, especially the ski boot, can affect a skier. More important, I have learned a lot more about the process with which to correct and reverse these effects so skiers whose progress has stalled, can reach a higher level.


On October 11, 2015, I received the following message from Matt:

“Hi David, I have been following your posts and discussion with interest. I’m a ski coach, I work 10-11 months of the year on snow. Summer in Australia and Winter in Whistler. I have a lot of questions for you. To keep it short, will you be in Whistler this season? And secondly, are you available for any amount of time to briefly discuss boot fit/make an assessment of me on/ off skis. I would be happy to pay any amount of money for your services.”

On October 22, 2015, Matt wrote:

“Thank you for your comments, it makes sense to read. Now my next question is…. Through the season could I look at creating the perfect boot and liner with you. Whilst I make do with my vacuum fit in the mean time, I’d like to invest and do this properly as I understand the critical importance of this.”

On October 26, 2015, Matt wrote:

“I appreciate all of your advice on the matters. In my years of skiing I’ve yet to have a boot where I’ve felt as if it’s the correct fit. Whether that be adverse effect in my feet or the outcome to my connection to the ski and snow!”

Matt knew that something was preventing him from realizing his potential.

I replied, “Once you have found a product you can work with, the process is not difficult.”

Feet First

The first thing I did was ask Matt to send me photos of his feet taken from top, sides and rear. Matt is solid and athletic. His problem is his feet, not in terms of their function, but in their inability to function within the constraints of pretty every performance ski boot.

In the photos below, Matt’s big toes are angled inward and twisted outward. His forefoot is also wider than performance boot shells, which are narrower than recreational boots. A big clue to Matt’s issues are the prominent heel spurs on both feet and the inflamed area outlined on the shank of his left foot. It was almost certain that his prominent inside ankle bones were in hard contact with the inside of the shells of his boots.

Although not as obvious, the front to back cross-section of Matt’s leg, above the ankle bone, appears big in proportion to the length of his foot. The mass of Matt’s calf muscle is also larger lower down on his leg than that of the typical elite skier. This issue is exacerbated by the large heel spurs that prevent Matt’s foot from moving all the way to the rear of the liner and boot shell.

Feet 2.1

Feet 1

Based on Matt’s photos, the most likely source of his problems was that the tongue of the liner of the boot was obstructing the glide path of his ankle joint. The lack of sufficient width was was limiting Matt’s ability to load the heads of his metatarsals, especially the head of the first metatarsal. This was preventing his foot from fully compressing and tensioning the arches. When Matt attempted to flex his ankles by moving forward in the hips, the center of force on tongue pressing on his shank was moving down the shaft of the boot into the glide path of his ankle. I discussed this issue in my posts:




As far back as 1987, the importance of ankle flexion and maintaining the center of force on the shin was recognized by a number of preeminent authorities.

In Kinematics of the Foot in the Ski Boot – Professor  Dr. M. Pfeiffer of the Institute for the Athletic Science at the University of Salzburg, Salzburg, Austria said, “The shaft of the boot should provide the leg with good support, but not with great resistance for about two thirds of the possible arc, i.e., (12 degrees) 20 to 22 degrees. Up to that point, the normal, physiologic function of the ankle should not be impeded. Previous misconceptions concerning its role in absorbing energy must be replaced by the realization that shaft pressure generates impulses affecting the motion patterns of the upper body, which in turn profoundly affect acceleration and balance.”

In Sports Medical Criteria of the Alpine Ski Boot – W Hauser P. Schaff of the Technical Surveillance Association, Munich, West Germany said, “Many alpine skiers have insufficient mobility in their knees and ankle. The range of motion, particularly in the ankles, is much too small”.

In Ski-Specific Injuries and Overload Problems – Orthopedic Design of the Ski Boot –  Dr. med. H.W. Bar, Orthopedics-Sportsmedicine, member of GOTS, Murnau, West Germany said, “Few forms of athletics place as high demands on the footwear used in their performance as alpine skiing. It (the ski boot) functions as a connecting link between the binding and the body and performs a series of difficult complex tasks. (my emphasis added) “The boot must assure freedom of mobility to the toes. This is accomplished by having a large enough inner shoe.

In my next post, I will discuss what’s wrong with ski boots in general.





Since the summer and fall is a time when racers and serious skiers make changes to their ski boots, I will describe the strategy I use to assess any changes. It is important to make changes in a manner that controls variables and provides a baseline to make one-on-one comparisons against. However, after viewing video provided to me by several followers of my blog that graphically show the effect on technique of changes made to ski boots over a number of years, it became apparent to me that few, if any, racers or elite skiers have any idea of what a ski boot should ideally feel like and especially how it should affect them in terms of performance.

Without clearly defined end objectives and a sequential process for achieving and confirming successful implementation, skiers and racers can only think in relative terms of better or worse, not optimal.

The experience of Mikaela Shiffrin at the beginning of last World Cup season serves as a prime example. Prior to the start of the 2014-15 World Cup season she changed boots. Early in the season, Shiffrin struggled. Thankfully, she regained her form after changing back to her old boots at a camp over Christmas.

In a similar manner, multiple Olympic and World Championship medalist, Julia Mancuso has struggled after changing boot brands. For the 2015-16 World Cup season she will be back on the boot brand she won her medals on. Will she return to her previous form? Hopefully, she will. But there is no guarantee.

These experiences are excellent examples of the perils of fixing something that ain’t broke and especially the need to have an escape route that allows a change to be undone that doesn’t work out for the better. Getting a boot right so it enables optimal user performance involves a degree of luck in addition to skill and knowledge.  As demonstrated by Shiffrin and Mancuso, no amount of talent can overcome a ski boot that is not right.

Good ski technique starts with a strong stance. In the order of things, the starting point is ensuring optimal performance of the human system by having a comprehensive biomechanical assessment done followed by a program designed to correct any deficiencies identified. The next step is stance training done outside of the ski boot in a controlled environment. This will be the subject of a future post.

Contrary to what is inferred by marketing pitches, ski boots don’t perform. They are inanimate objects. What ski boots do is influence the performance of the human system. Skiers and racers do the equivalent of chasing the rainbow by searching for the right boot in the absence of a definitive specification for what the right boot for them needs to be. Comfort is often erroneously used as a benchmark for performance. Although a boot that supports user performance must be comfortable, comfort, in itself, does not equate with optimal user performance. A boot can be very comfortable while severely compromising skier performance. As the impediments to performance are sequentially removed, a boot that started off being comfortable typically starts to become increasingly uncomfortable as the most prominent sources of interference to function reveal themselves and does not become comfortable again until all sources of interference are removed

The following is part of general strategy strategy for assessing changes in ski boots:

  • Do not change components of a ski boot such as liners and insoles without the ability to reverse the changes.
  • When changing to a new boot model or boot brand retain the old boots. If doubts arise about the new boots  one-on-one comparisons can be made with the old boot on one foot and the new boot on the other.
  • If possible, try the shell of a new boot with the liner inserted in it from the old boot and do a one-on-one comparison with the old boot. This eliminates differences in liners and can give a good idea of how the new shell compares to the old shell.



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.


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.


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.


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.


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,


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 in the video 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.

Section R

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.


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.



The first thing I look for in a ski boot I am considering is a shaft with sufficient stiffness to create a defined oval shape that will accommodate 14-15 degrees of lead segment low resistance ankle flexion before firm contact of my shank with the front of the shaft occurs. Because my shank is free to move fore and aft up to 14-15 degrees within the shaft, I tend to be acutely aware of what the tongue is doing on my shin. This is much harder to sense in boots with flexible shaft overlap segments that won’t assume a defined shape and especially in a boot with the shaft buckles and power strap cinched tight. When I took my Head World Cup boots out of the box and put them on I immediately sensed the tongue pressing firmly against the base of my shank. This was before I even tried to dorsiflex my ankle (rotate my shank forward). The curve of the transition of the tongue felt like a block pushing against the base of my shank.

Most plastic tongues amount to bent half tubes. One of the stiffest shapes known is a tube. When the trailing edges of a ski boot tongue are loaded by the leading edges of the boot liner and the curved interface of the boot shaft, the shank portion of the tongue becomes substantially rigid. When the shank presses against the tongue it bends at its transition with the forefoot portion. When it bends, the curve at the transition flattens and the tongue body moves rearward towards the shank. Unless the tongue is sewn to the toe box of the liner so it is too far forward, it can press on the lower end of the shank and block the glide path of the ankle joint. Here is a simulation of what happens. The black line represents the profile of the tongue.


This issue was identified in my US No. 4,534,122 and in a series of X-ray video studies done by Professor M. Pfeiffer (Kinematics of the Foot in the Ski Boot – The Shoe in Sport).  In the Type C study Dr. Pfeiffer observed that, among other things, the physiologic function of the ankle is stopped prematurely (blocked) with the effect that the talus (the bone that forms the ankle joint with the tibia) is levered backward and upward within the boot shell. The previous short video clip and the clip that follows below show this effect. If you pause the videos before and after shank loading you can see the extent of the effect of the tongue bending at the transition and pressing against the base of the shank. The flattening effect at the transition is due to the manner in which the stiffness of the half tube shape of the tongue influences the deformation.


Note how the foot is forced backward in the boot and the entire forefoot lifts off the boot board. This effect is easy to demonstrate with foot pressure technology by having the subject apply firm pressure to the balls of the feet and then flex the boot. As boot flex progresses, the pressure seen on the monitor under the balls of the feet will progressively decrease then disappear. The reason for this is that ski boots are flexed by decreasing the contraction of the soleus muscle. This has the effect of turning off the connection of the tibia with the balls of the feet. In his article, Dr. Pfeiffer stresses the importance of the forces on the shank in the fore aft plane being the result of active muscle participation and tonic muscular tension and that if muscular function is inhibited in the ankle area, greater loads will be placed on the knee. Tonus in a muscle is a reflex state where the muscle is primed and ready to rapidly respond to a neural signal to contract.

In my next post I will discuss the modifications I make to my boot tongue to try and minimize ankle glide path block.




In reference to the photo of the tongue, which I surgically removed from the liner of my Head World Cup ski boot with a tonguectomy procedure, I also performed a bilateral resection of the tongue for the purpose of exposing the core structure. The photo on the right is of the resected tongue . I will discuss this tongue in the next post. I apologize for any confusion this omission may have caused.

Tongue section


This post is about how tongues in ski boot can affect balance.

Every ski boot has some sort of tongue. In the case of rear entry boots or liners like the Intuition, a portion of the liner acts in the capacity of a tongue. So what exactly does the tongue do? The obvious job of the tongue is to the pad the shin and spread the load applied by the shank to the front of the boot shaft.

What about the forefoot portion of the tongue over the instep of the foot? What does it do? As far as I have been able to ascertain, for most skiers, not much. Seriogram X-Ray studies done for me in 1995 found that in the boots of some skiers, there was a significant crash space between the top of the forefoot portion of the tongue and the inner surface of the boot shell. A lack of constraint or load applied to the instep of the foot of a skier means that the entire foot can float within the boot shell in response to perturbations in snow reaction force. Typically, when a skier’s CoM is perturbed, the plantar foot separates from the insole on the liner. If the skier is thrown off balance and pitches forward, the heel of the foot moves up as the foot rotates about the balls of the foot. This is an issue that the in-boot technology in my US Patent No. 4,534,122 addressed.

But ski boot tongues can do other things that you may not be aware of. The tongue can act in the capacity of a spring that opposes and progressively loads the shank in ankle flexion. Worse, it can  obstruct the glide path of the ankle joint. When the now ubiquitous power strap that is present on most boots today is cinched up tight, the tongue can act as an effective splint for the ankle.

In my last post, MOMENT OF THE SHANK IN THE SHAFT,  I used a simulation to show how my shank can move with little resistance from the shaft for about 14-16 degrees within the front to back free space within the shaft. In his article, Kinematics of the foot in the ski boot, Dr. M. Pfeiffer refers to this as the lead segment of shank flexion. Here is what it looks like in my Head World Cup ski boot.

Lead segment

The red line emanating from the fixation of the shaft of the boot indicates the proximate point about which deformation of the front of the cuff will occur. As my shank encounters the front of the shaft I want the load centre to remain substantially fixed and the resistance to predictably increase so my balance system can work with it.

The load applied by my shank is to the top edge of the front of the shaft of the boot. This is the centre of the load. The load is distributed by the tongue above and below the load centre. I like to have a little more load on my shank below the load center than above the load centre. The red arrows and bar with the dots in the photos below show this. I don’t want to have any load on my shank below the lower aspect of the load distribution.

C of Force

Here is what the stock tongue from my boots looked like after I performed a tonguectomy procedure that removed it from the liner.

Tongue section

Here is what the tongue looks like overlaid on my ski boot.

Tongue overlaid

Note the flat profile. In order for the tongue to conform to my foot and leg either my ankle has to severely plantarflex or my the tongue has to bend. I suspect that tongue is made this way to act as a sort of shank-shaft  shoehorn to facilitate entry of the foot into the boot. Since I can’t stand up let alone ski with my ankle plantarflexed, the tongue has to bend. By what? By my shank applying a force to it. In this configuration the tongue is acting like a spring pushing against the shank of my leg in places where I don’t want any load.


I push on the tongue, the tongue pushes back. But it can be worse than that especially if the tongue is too far back as it was in my boots. The tongue is fixed (usually sewn) to the toe box of the liner. The first time I put my boots on (the liners were intact then) and operated the buckles it felt like a steel rod was jammed into the base of my shank. If I tried to flex my ankle I could feel that the glide path of the joint was impeded. So I would get an initial load on my shank at its base followed by a secondary load at the top of the shaft superimposed over the first load. To me, the feeling is like running up a flight of stairs and catching the toe of my lead foot on a stair nosing. I call this kind of unpredictable loading the ‘trip effect’ because it feels similar to tripping in terms of the effect on my balance.

In my next post I will discuss the tongue modifications I typically make.