perfect fit


I originally published this post on May 12, 2013. This is a revised and edited version.

Before I started ‘tinkering’ with ski boots in 1973, I didn’t just read everything I could find on the subject of fitting boots, I devoured every bit of information I could find on the subject. The assumption I made at that time was that the experts in the field not only knew what they were talking about, but that they also had the requisite knowledge and understanding of the underlying principles to back up their positions with applied science and/or research. Based on this assumption, I started modifying ski boots by doing all the things the experts recommended such as padding the ankle to ‘support’ and ‘stabilize’ it in the boot shell and cuff and adding cants between the soles of the boots and the skis to make the skis sit flat on the snow. But the big breakthrough for me came when I started making footbeds to support the foot.

Within a year I had gained expertise in my craft to the point that skiers from all over Canada were starting to seek out my services. In  response, I started a company called Anatomic Concepts. Soon, I was spending most of my free time working on ski boots. But while I was helping a lot of skiers ski better, none of what I was learning or doing was helping my own skiing. I was still struggling after switching from low-cut leather boots to the new stiff, all plastic boots.

The (Un)Holy Grail

Despite the inability to solve my own problems, my thinking remained aligned with conventional thnking right up until my experience with Mur and the ‘Holy Grail’ of ski boots; the perfect fit of the boot with the foot and leg of the skier.

In 1977, Roger McCarthy (head of the Whistler Ski Patrol), whose boots I had worked, on introduced me to Nancy Greene Raine in the Roundhouse on top of Whistler Mountain. The timing was perfect. Racers on our National Ski Team were having boot problems. They needed help. It was a classic case of me being in the right place at the right time. Nancy recruited me, flew me to Calgary at her expense and introduced me to the National Team and Dave Murray. She set up a working arrangement with the team, one in which I was completely independent. Nancy also introduced me to Glen Wurtele, head coach of the BC Ski Team. At Wurtele’s request, I began working on the boots of members of the team.

I started working on the boots of NAST (National Alpine Ski Team) racers with Dave Murray; ‘Mur’ as he was affectionately known. My thinking at that time vis-a-vis the need to immobilize the foot and achieve a ‘perfect fit’ of the boot with the foot was aligned with the approach of the  ‘experts’ in the  field. Mur didn’t live far from me. When I was working on his boots, he seemed to spend more time at our home than his. Because of my ready access to Mur, I saw an opportunity to achieve the Holy Grail of skiing with a fit of the boot with the foot so perfect that the foot was for all intents and purposes rendered rigid and immobile and united with the structures of the ski boot.

To achieve this lofty goal I spent the better part of 2 weeks working for hours every night carefully crafting a matrix of heat formable 1 mm thick vinyl around Mur’s foot and leg and the shells of his boots with my inserts inside the liners of the boot. When Mur finally confirmed he was ‘loaded, locked and ready’ he went skiing to test the results. I waited for the inevitable confirmation of success and certain celebration that would follow. But after what seemed like an eternity, instead of the expected good news, Mur called to tell me that he could barely ski with my perfect fit. He had little or no balance or control. The Holy Grail had reduced a world class skier to a struggling beginner. I didn’t need to be a rocket scientist to know that the industry had to be way off track especially in view of the recent publication of Professor Verne T. Inman’s seminal book, The Joints of the Ankle.

After this experience I knew that there was way more going on than I understood. I started learning about human physiology, in particular, about the mechanics, neuralbiomechanics and physics of skiing. I started asking hard questions that no one in the industry seemed to have answers for. And I started going off in a very different direction from the one the industry was acquiring increasing momentum in. If the perfect fit could impose what amounts to a severe disability on one of the world’s best skiers I could only imagine what such indiscriminate constraint was doing to the average recreational skier. It could not be good. For me it certainly wasn’t.

A major turning point came for me in 1988 when a husband and wife radiology team who had heard about my efforts to try and develop a ski boot based on anatomical principles presented me with a copy of a medical text called The Shoe in Sport published in German in 1987. This seminal work contains an entire chapter dedicated to The Ski Boot. I discuss the issues raised about the design and fabrication of ski boots by international experts in the articles in chapter on The Ski Boot in my most viewed post to date; THE SHOCKING TRUTH ABOUT POWER STRAPS (1.)

The Root of Misinformation

Unfortunately for skiing, the relevance and significance of the knowledge contained in The Shoe in Sport was overshadowed by the publication in 1971 of the book, the Biomechanical Examination of the Foot, Volume 1 by Drs. Merton Root, William Orien, John Weed and Robert Hughes. The book lists what the authors call their “Eight Biophysical Criteria for Normalcy”. These criteria, which have since been challenged and shown to be largely invalid,  were claimed to represent the “ideal physical relationship of the boney segments of the foot and leg for the production of maximum efficiency during static stance or locomotion”.

A key component of the biophysical criteria was that a bisection  of the lower third of the leg be perpendicular to the ground and the subtalar joint rest in neutral. Root described neutral as occuring when the subtalar joint was neither supinated or pronated.

In order to be considered normal, a foot had to meet all eight biophysical criteria. The effect of this criteria, which was arbitrary, was to render the majority of the feet of the world’s population abnormal and candidates for corrective interventions. Although Root never stated, implied or suggested it, his neutral sub-talar theory appears to have been misinterpretated in the ski industry to mean that the foot functions best in static ski stance when its joints are immobilized in neutral (sub talar).

In recent years, Root’s Sub-Talar Neutral Theory has come under increasing challenge with calls to discontinue its use (2.).

Taken as part of a wider body of evidence, the results of this study have profound implications for clinical foot health practice. We believe that the assessment protocol advocated by the Root model is no longer a suitable basis for professional practice. We recommend that clinicians stop using sub-talar neutral position during clinical assessments and stop assessing the non-weight bearing range of ankle dorsiflexion, first ray position and forefoot alignments and movement as a means of defining the associated foot deformities. The results question the relevance of the Root assessments in the prescription of foot orthoses.

The results of the wider body of evidence have the potential to have profound implications for skiing in terms of the application of Root’s Subtalar Neutral Theory as putting the foot in the most functional position for skiing by supporting and immobilizing it in neutral (subtalar).



In this post, I will expand on the content of The Shocking Truth About Power Straps (1.) which was by far the most popular post since I started this blog in 2013.

While the truth about what power straps can potentially do if improperly adjusted is shocking, the lack of support in principles of applied science for the basic premise that I describe as indiscriminate envelopment as the approach to achieving a fit of a ski boot with the foot and leg of the user with the objective of substantially immobilizing it’s joints with unknown consequences, is even more shocking. Little or no consideration appears to be given to the effects of indiscriminate envelopment on the balance and motor control systems of the skier.

What is done to the foot and (lower) leg can affect the entire body. In his post, Foot biomechanics is dead. Discuss (2.), Professor Chris Nester states:

The foot is not a compilation of interconnected mechanical components that respond precisely to the laws of mechanics. It is a complex matrix of at least 11 biological tissues (i.e. skin, fat, muscle, tendon, joint capsule, ligament, bone, cartilage, fascia, nerves, blood vessels….) that responds to external loads through the symbiotic relationship between the motor control system and tissue properties.

Professor Nester goes on to state:

I believe the integration of our current foot biomechanics knowledge with insights from motor control, neurophysiology and related domains (e.g. tissue biology) will drive advances in foot function more than pursuing a pure mechanics paradigm.

Professor Nester proposes that the term biomechanics be replaced with the term Neurobiomechanics. I concur.

How Does the Ski Boot Affect the Human Performance of the Skier?

The short answer is that when the structures of a ski boot indiscriminately envelop the structures of a foot and a portion of the leg (aka the Perfect Fit or the Holy Grail), no one knows. While it is essential that a ski boot create a secure connection of the foot of a skier with the ski, it should not achieve this connection at the expense of natural neuromuscular function, especially balance.

In 1980, when I was about to prepare a new pair of Lange race boots for Steve Podborski, I asked myself whether it was possible to obtain a secure connection of the foot with the ski without compromising natural neuromuscular function or, even better, was it possible to enhance natural neuromuscular function?

I took a significant step towards answering this question in 1980 when I designed and fabricated a device I called a Dorthotic. The Dorthotic supports the upper or dorsal aspect of the foot as opposed to supporting the plantar aspect (i.e. the arch). My theory that loading the top of the foot or dorsum with a force perpendicular to the transverse or medial-lateral plantar plane of the foot has positive benefits for motor control and balance has begun to be recognized. The Dorthotic enabled Steve Podborski to compete and win on the World Cup Downhill circuit mere months after reconstructive ACL surgery and to eventually win the World Cup Downhill title, a feat no non-European has repeated. US and international patents for the dorsal device were awarded to me (David MacPhail) in 1983.

The success of the Dorthotic gave me a start towards answering the question of whether a secure connection of the foot with a ski was possible without compromising natural neuromuscular function. But I knew that I needed to learn a lot more. I realized that finding the answers I was seeking and especially unraveling the secret that enables the world’s best skiers to stand and balance on their outside ski, would require a multi-disciplinary approach.

The Missing Factor in Skiing: A Multi-Disciplinary Approach

A significant influence that served as the impetus for the design of the Birdcage research vehicle and the on-snow studies, was the work of Dr. Benno Nigg. In 1981, Dr. Nigg accepted an invitation to move from ETH Zurich, where he was the director of the biomechanics laboratory, to the University of Calgary, where he founded and developed the Human Performance Laboratory (HPL), a multi-disciplinary Research Center that concentrated on the study of the human body and its locomotion.

The publication of the Shoe In Sport in English in 1988 served as a seque to introduce me to Nigg’s research at HPL. Studies done at HPL found that any interference with the function of the human foot, even a thin sock, extracts a price in terms of the adaptive process the human body has to undergo to deal with what is really an externally imposed disability.

The Effect of Footwear on the Neuromusculoskeletal System

There is an excellent discussion in a recent post on the Correct Toes blog (3.) on the impact of a narrow toe box, toe spring and elevated heel of traditional footwear on the human body. Elevating the heel in relation to the forefoot will predictably cause a realigment of the ankle-knee-pelvis joint system with a corresponding adjustment in the tension of the associated muscles with a global effect on the Neuromuscularskeletal System. This has been known for decades. Elevating the heel in relation to the forefoot, will cause the ankle joint to plantarflex (reduce dorsiflexion) in relation to the support surface under the foot in order to maintain COM within the limits of the base of support.

Ramp Angle Rules

Due to the unstructured nature of the indiscriminate envelopment characteristic of the fit of the majority of conventional ski boots, it is extremely difficult, if not impossible, to determine the effect of constraint of this nature on the Neuromusculoskeletal System. So I’ll focus on the one aspect of the ski boot that has consistent and profound implications on skier human performance, especially motor control and balance; boot board ramp angle or zeppa. Binding ramp angle or delta compounds any effect of zeppa. For the sake of simplicity we’ll assume zero delta.

Contrary to the widely help perception, raising the heel of a skier in a ski boot does not cause CoM to move forward. In fact, it usually has the exact opposite effect. It puts a skier in the back seat with the weight on their heels. Worse, it can disrupt the competence of the biokinetic chain that dynamically stabilizes and protects the joints of the lower limbs. Excessive heel elevation can render a skier static and cause the balance system to resort to using the back of the shaft as a security blanket.

As of this writing, I am unaware of any standard within the ski industry for zeppa. It appears to be all over the map with some boots having as much as 6.5 or more degrees. The default zeppa for the human foot on a hard, flat level surface, is zero.

Through subjective experiments in 1978, I arbitrarily determined that zeppas in excess 3° had a detrimental affect on skier balance. In 1991, zeppas of 2.3° and 2.5° were chosen for the large (US 8-12) and small (US 4-8) Birdcages based on an analysis of the effect of ramp angle on COM and neuromuscular activity. This range appears to work for a majority of recreational skiers. But recent tests with a dynamic ramp angle assessment device that I designed and fabricated is finding the stance of elite skiers optimizes at much lower zeppa angles, with some skiers below 1.5°. Interestingly, when NABOSO insoles are introduced for the assessment, zeppas decrease even further. With minimal training, most skiers are sensitive to dynamic changes in zeppa of 0.1 degrees.

Implications for the future of skiing

A tectonic shift is underway on a number of fronts (see A Revolution) that is challenging the mechanical and static premises that form the underpinnings of the key positions in ski teaching and the design of equipment such as ski boots and the fit process. In my next post I will post recent material by Dr. Emily Splichal, functional podiatrist and inventor the revolutionary NABOSO small proprioceptive stimulating insole.



When I started modifying ski boots in 1973, my perspective was that the problems that I was experiencing with my own skiing after switching from low-cut leather boots to the new higher, rigid plastic boots was an improper fit of the boot with my foot and leg. The paradigm back then, one that persists today, is that the optimal fit of the ski boot is achieved when the fit of the boot perfectly mirrors the shape of the user’s foot and leg. A related perception, that also persists today, is that the design of activity specific footwear is based on sound principles of science and that the footwear supports the performance of the human system.

I went forward on the basis that the conventional paradigm was both valid and based on sound principles of science. But instead of the expected improvement in performance commensurate with improvements in the application of the principles of the established paradigm, I was seeing a decrease in performance. As this continued to happen, I began to question everything I had initially accepted as factual and sound. When I did, I started heading in a new direction. A few Einstein quotes are appropriate.

We cannot solve our problems with the same thinking we used when we created them.

Insanity: doing the same thing over and over again and expecting different results.

A man should look for what is, and not for what he thinks should be.

Starting in the fall of 1978, I began to look for what was, instead of looking for what I believed should be. One thing Einstein didn’t appear say is that human thinking seems to follow Newton’s Laws in that once a paradigm becomes accepted it tends to develop momentum that resists new thinking. Right or wrong, it seems to be human nature to stay with the familiar. This is especially true once a paradigm has acquired commercial momentum. In terms of contemporary knowledge of functional anatomy, the thinking in the footwear paradigm, even today, is by comparison, at best, stone age.

Once I stepped out of the conventional footwear paradigm it became obvious to me that, with rare exceptions, the majority of footwear today, including ski boots, is predicated on a 5,000 year old, unsophisticated, cobbler-paradigm of wrapping a sole structure over and about the foot and leg of the user. Like Henry Ford’s dictum, You can have any color you want as long it is black, the consumer today  is faced with a similar You can have any form of footwear you want as long it is based on a 5,000 year old artisan format. That a 5,000 year old footwear paradigm remains substantially unchanged in our digital age tends to foster the perception in the consumer that activity specific footwear such as sport shoes is conducive to proper biomechanical function. This premise is largely accepted without question. But in the following statement contained in the introduction to The Shoe in Sport  (published in 1987), the authors suggest, that far from being conducive to proper biomechanical function, footwear may, in fact, actually be causing problems.

“Is there really a need for shoes? The examples of athletes like Zola Budd and Abebe Bikila suggest

……. in a technologic environment the evolution of the athletic shoe parallels the decline in our organs of locomotion.

The authors go on to state,

The buyers of athletic shoes are always looking for the ‘ideal shoe’. They encounter a bewildering variety of options and are largely dependent for information on the more or less aggressive sales pitches that are directed at all athletes in all possible ways. For this reason, the ‘shoe problem’ as it exists in the various fields, will be studied (in the book) with respect to the biomechanical, medical and technical aspects of shoemaking. The findings (of the studies contained in the book) should enable the interested reader to distinguish between hucksterism  and humbug on one side and the scientifically sound improvements in the athletic shoe on the other(my emphasis added).

The reference to hucksterism rings true with some of the statements made by ski  industry tech and ski magazine writers that are so  patently absurd as to be offensive to anyone with a modicum of knowledge of functional anatomy. In 1978 when I first began to suspect this was the case, I diverged from convention and started looking in new directions. I started asking questions that no one had answers for.

When I began to conduct subjective experiments that called into question the principles on which ski boots were based, I got a clear indication that I was displeasing certain parties in the memo below received by National Team racers and forwarded to me.

NAST 79 memo

I found the memo especially interesting in view of the fact that my services had been requested by Nancy Greene Raine because National Team racers were not getting the help they needed with their boot problems.
Silence in the face of knowledge of a better way to do things only serves to perpetuate ignorance and dogma. Constructive, honest criticism, offered in the spirit of furthering a cause or effort, is the catalyst of innovation and progress. Constructive, honest criticism is also a catalyst of learning. Towards this end, my commitment has been, and continues to be, to the athlete and the realization of their true performance potential.


Here is what I said in my US patent (since expired) that I wrote in January 1991 and filed on February 3, 1991 about the existing philosophy in ski boots (aka – the prior art)

“The inventive technology disclosed by the present application, as will be described in more detail below, teaches the importance of accommodating and enhancing both bipedal and monopedal function by providing for freedom of medial movement of the inside ankle bone. This is in direct contrast with the prior art which teaches, in an indirect manner, that the ideal function for skiing will result from fixing the architecture of the foot in a position closely resembling that of bipedal function, thus preventing monopedal function. 

The prior art refers to the importance of a neutral sub-talar joint. The sub-talar joint is a joint with rotational capability which underlies and supports the ankle joint. The sub-talar joint is substantially “neutral” in bipedal function. That is to say that the foot is neither rolled inward or rolled outward.

If the foot can be substantially maintained in a neutral position with the arch supported and with a broad area of the inner aspect of the foot well padded, there will exist a good degree of comfort. Such a state of comfort exists because the foot is not able to roll inward (pronate) to a degree where significant mechanical forces can be set up which would allow it to bear against the inner surface of the boot shell. In effect, this means that initiation of the transition from a state of bipedal to a state of monopedal function, is prevented. This transition would normally be precipitated by an attempt to balance on one foot. If the foot is contained in a neutral position, traditional supportive footbeds (arch supports) are quite compatible with the mechanisms and philosophies of the prior art.

COMMENT: The objective of the conventional ski boot, whether intended or not, is to make skiing exceedingly difficult. Towards this end, the objective is comfort. A ski boot that renders the lower limbs dysfunctional can be very comfortable while at the same time making skiing exceptionally difficult. Although a priority, comfort in itself does not necessarily equate with good balance and control in skiing.

Problems arise when the foot is attempting a transition from a state of bipedal stance to monopedal stance. If the transition to monopedal stance or function can be completed without interference from the structures of the ski boot, all is fine and well. However, if the transition is allowed to proceed to a point where the mechanics associated with the monopedal function can establish significant horizontal forces, and the further movement of the foot is blocked before the transition can be completed, the skier will experience pain and discomfort at the points where the inner aspect of the foot bears against the structures of the footwear. This is the situation experienced by a majority of the skiers with prior art footwear. It is at this point where arch supports, if employed, also begin to cause discomfort. It should be noted that it is the normal tendency of the foot to pronate when weight bearing on one foot.

Footbeds (arch supports) may work in conventional boots (which traditionally do not allow natural biomechanics or movement of the foot to occur), but in a boot which accommodates and supports natural leg and foot articulation and function, arch supports can be detrimental.

When the foot attempts to pronate inside the ski boot, it is often the case that the ankle bone will come to bear against the inner surface of the boot shell. When contact of this nature occurs, pain and other related complications usually result. Since the consensus of those skilled in the art of ski boot design and modification is that pronation or the rolling inward of the foot is detrimental, and, thus, undesirable, provision is not made to allow for such movement. Rather, the structure of the footwear is intended to resist or even prevent it.

Thus, the problem with existing footwear arises due to the dynamic nature of the architecture of the foot. When the wearer is standing with the weight equally distributed between left and right feet so that the centre of mass of the wearer is manifesting itself in the centre between the feet, the architecture of the wearer’s foot assumes a specific configuration. As the wearer begins to shift his weight towards one foot so that the other foot bears proportionately less weight, the wearer’s centre of mass moves over the medial aspect of the weighted foot so as to assume a position of balance.

In order for this movement of the wearer’s centre of mass to occur, the architecture of the weighted foot must undergo a progressive re-alignment. Existing footwear does not adequately anticipate this re-alignment of the architecture of the foot and thus such footwear inhibits the wearer’s ability to assume a balanced position.”

While I am working on the video cited in my last post I will do a post next that describes how to assume a pronated position on one the foot and what it feels like.


In order to get the best connection of the foot with the ski the boot must fit the foot as closely and as tightly as possible. Race boots need to be narrow in forefoot, significantly narrower than recreational boots, so that the boot will grip the forefoot tightly for ‘optimal steering’ control. We know these things to be true because that’s what the experts preach, or at least that’s the official story. If everyone agrees on an issue then consensus equals truth. In my case, I knew this was true because I couldn’t seem to get a tight fit of my feet with my ski boots. Other skiers must have been having the same problem because in the ’70s improving fit was a common theme of ski magazine articles on boot fitting. And there was an array of ankle pads and other aids available to help tighten the fit.

If one had a loose fit of their foot in their ski boots the answer was simple; improve the fit with pads or foam injected liners that precisely conform to the shape of the foot. Today heat formable liners and even heat formable boot shells, considered by some to be the Holy Grail of skiing, are available as are boots formed to lasts made from 3 D scans of the user’s foot. Perfection draws closer. That all boot fit technology has gravitated towards the perfect fit serves to prove the soundness of the concept………or maybe not. Maybe there is something else going on.

First, let’s be clear. The foot must be constrained in some fashion to achieve an intimate connection with the ski. But what I started to notice is that the feet of elite skiers were different in a fundamental way from those of lesser skiers whose feet were in turn different from the feet of those (of which I was one) who were struggling to ski in rigid plastic ski boots. Specifically, the feet of the elite skiers were compact and seemed tighter than the feet of lesser skiers. What do I mean by tighter? The foot has 28 bones that shift in relation to each other in three-dimensional space. The movement of the bones is constrained by soft tissue, in particular  ligaments that bind the bones together. The movement of the bones of the feet of elite skiers seemed to be more constrained by ligaments than the bones of the feet of lesser skiers. Put another way, the feet of elite skiers appeared to be able to function reasonably well within the constraints of the rigid plastic ski boot.

An excellent animation showing the movement of the bones of the foot called, ‘Ankle & Subtalar Joint Motion Function Explained Biomechanics of the Foot – Pronation & Supination by Dr Glass DPM’ can be viewed at –

The problem is that in an industry where the foot is represented by an inanimate one-piece last, the tendency is to view all but the most deformed feet as equal. Clearly this is not the case. Research on foot characteristics has classified the human foot into three categories; 1) tightly bound, 2) moderately bound and, 3) loosely bound. If your feet fall into category 1), tightly bound, and your foot is compact with moderate or less width, the odds are that you will find skiing easy. Category 2 is less certain while category 3), of which, I was one, means that attempts to tighten the fit of the ski boot could, and usually do, actually make the bones of the foot looser because the structures of the boot interfere with the processes that tighten the bones of the foot. This results in a perceived looseness of the foot, which can lead to subsequent attempts to tighten the fit of the boot resulting in a vicious circle.

Recognizing that foot structure can affect the ability to ski adds a layer of complexity, one that marketers would probably rather ignore. The essence of effective marketing is simplicity. “Watch what I do. Listen to what I tell you to do and you will ski like me”. Easy! Except for the fact that for the majority it doesn’t work this way. They may try their best to ski like the best. But the simple fact of the matter is…….they can’t because of their type of foot type. Like the earth is flat story, once people buy into concept they tend to stick with with it even in the face of overwhelming evidence that it is flawed. The brain subconsciously filters out any information that disagrees with the official position. So those with loosely bound feet “don’t get no respect”.

But it gets worse. Skiers with tightly bound feet tend to ski with their boots loosely buckled. Cases have been documented of racers winning races who had forgotten to close their boot buckles. Skiers with tightly bound feet usually ski best with loosely buckled ski boots, something those with loosely bound feet would find unthinkable. The resulting Paradox flies in the face of the common sense. So it is conveniently ignored. Skiers with tightly bound feet usually end up being the ski pros by a process of elimination. The best feet rise to the top. Because the best skiers tend to assume that skiing is a simple matter of teaching someone to do what they can easily do, they don’t appreciate, let alone understand, why others can’t seem to get it.

In summary, loosely bound feet require much more three-dimensional space in which to acquire tightness than tightly bound feet. Tightly bound feet function best in minimally tensioned ski boots. But maximal constraint can never make loosely bound feet tight because a tight fitting boot inhibits the physiologic processes that tighten the joints of the foot. Knowing this, I knew that the answer had to be to find a way to constrain the foot in a manner that allowed the tightening processes of all types of feet to engage. If this were possible all feet would become equal. In effect, this would serve to level the playing field or perhaps better stated, make the slope more consistent for everyone.


In LESS REALLY IS MORE I talked about how I gone in a direction opposite from that of the industry after my perfect fit experience with Mur. I was now removing material from ski boots instead of adding material and expanding shells where necessary to make room for the structures of the foot. While this seemed to generally have a positive effect on skier balance and the ability to control skis, especially edging, removing material from the sides of the boot liner  exacerbated the fact that in the majority of cases I was encountering the shell wasn’t loading the instep of the foot. The reason for this turned out to be  that there was a void between the top of the tongue of the liner and the inner surface of the shell over the forefoot. This was allowing the foot to move upward into the void space or unload from contact with the sole plate (aka boot board) in response to changes or perturbations in ground reaction force. I coined the effect Separation Anxiety because of the alarm bells it was setting off in the skier’s balance system.

After I became aware of this effect, I started doing experiments to try and understand how it was affecting a skier’s balance and ability to control their skis. While riding ski lifts with foot rests (the old slow chairlifts) I would let one of my feet drop off the foot rest and try and feel what was happening with my foot and leg inside the boot when the foot unloaded from the boot board. At that time, I wasn’t thinking in terms of trying find a solution for knee injuries. I saw this as an issue that would be addressed by refinements in bindings which at that time were rapidly evolving. Through my experiments I had come to the realization that the unloading and reloading of the sole of the foot with the boot board, such as occurs when a skier is moving over irregular terrain, was setting off a chain-reaction of physiological events that were creating balance issues. Although I didn’t know exactly how, this unload/load cycle  seemed to be placing stress on the knee. But my focus was trying to find a way to reduce the effect on skier balance. In effect, I was trying to achieve a net improvement in skier balance by reducing negative balance artifacts.

The standard solution in those days was to attempt wedge the heel with heel or L-pads inserted in the liner. The objective was to keep the foot from lifting. I tried this approach. But I  found it didn’t work as advertised. The pads invariably caused problems with the Achilles tendon or they prevented the heel from seating in the back of the shell, or both. The latter had the effect of making the liner shorter and the boot hell to put on. I was looking for a better solution. But it wasn’t until 1980, while working on Podborski’s boots, that I came up with a device that eventually led to my being granted US Patent Number 4,534,122.


When I started skiing in 1970, the buzz was all about the new safety bindings. Debates raged in magazines and ski shops over which binding was the best as in the safest. After years of skiing being perceived as dangerous because of the incidence of broken legs, a new era had arrived with the introduction of a generation of sophisticated bindings. This created the perception that it was finally safe to go out play on the ski hills. But as the sound of snapping leg bones faded into the background it was replaced by an even grimmer sound; the popping of knee ligaments, in particular, torn ACLs. Before the introduction of the rigid plastic ski boot, few skiers had ever heard of an ACL. That was about to change.

It was about the time that I started working with National Ski Team members in 1977 that I began to hear of racers suffering knee injuries. Knee injuries seemed to start with a trickle. I can’t even recall hearing of a recreational skier suffering one. Like most skiers, I believed that the new bindings had addressed the injury issue. Even after knee injuries started to increase in frequency I thought it only a matter of time before refinements would be made to ski bindings and that this would be the end of them. As the popping of ligaments got more frequent, panic seemed to set in in the industry. Skiing had entered a period of vigorous growth. The last thing it needed was a good news, bad news story as in, “The good news is that the rigid plastic boot has made skiing easier. Now for the bad news…..”. As best I can recall, it was around 1980 that a team of spanish orthopaedic surgeons published a study linking the introduction of the rigid plastic boot to knee injuries noting that the incidence appeared to be rising in lock-step with sales of the boot. A classic problem-solving strategy is to go back to the time when a problem first emerged and look for anything that changed. In this case, the most significant change was in the boot. Meantime, those with expertise in biomechanics were pointing out that by stiffening the ankle the boot was sending the forces of skiing upward to the relatively weak knee.

In retrospect, it seemed like it should have been obvious that encasing the foot within what amounts to an orthopedic splint would act to transfer force up the leg. It’s ironic, if not erroneous, that the industry, even today, talks about the boot transferring energy to the ski as if this were the end game of skiing. The reality is that unless the ski industry has repealed Newton’s Third Law (which is doubtful), if a skier were to transfer energy to anything through the boot it would be through the stack of equipment between the sole of the boot to the source of Ground (or Snow) Reaction Force at the snow. This being the case, according Newton’s Third Law which states; “For every action there is an equal and opposite reaction”, the snow will transfer an equal amount of energy through the stack of equipment back up the skier’s leg to the knee. The issues are way more complex than a simple transfer of energy. But I will start with the simple and obvious then build from here.

The question is, “Given the established reputation of skiing as being a dangerous sport prior to the introduction of the rigid plastic ski boot and the fact that skis attached to the foot and leg act as force multipliers, did anyone consider the implications of trying to immobilize the foot and leg within a rigid plastic ski boot?”