Foot Function posts

WHY TRYING TO COPY HIRSCHER AND SHIFFRIN’S MOVES DOESN’T WORK – PART 4

A central premise in skiing, especially in ski teaching and coaching, is that skiers and racers can learn to ski like the best by observing and copying them. Hence, articles and videos that talk in nebulous terms about good balance, an athletic stance, pressure control, steering, edging, extension, separation etc. as elements that, when blended together, will enable skiers and racers to ski like the Hirschers and Shiffrins of the world. If a racer who has undergone training in the system is not competitive or worse, suddenly becomes uncompetitive, the racer is typically blamed for not being strong enough or not pushing themselves hard enough or not taking enough risk or some other factor. In the end, the responsibility for lacklustre performance is conveniently assigned to the racer.

Ski boots are rarely considered a factor. So long as the boots are comfortable that is the only thing that matters. To suggest otherwise is to blame the equipment. This flies in the face of my experience. But until the skate study (1.) I had no reliable way of measuring and thus comparing performance.

The two pressure studies done in 1998 by the University of Ottawa with elite ski instructors provided an opportunity to compare the results of the studies to those of the 2012 skate study that I modified skates for. This study was also done by the University of Ottawa. Of the three studies:

  • One 1998 skier pressure study used three highly skilled ski instructors (CSIA level IV)
  • One 1998 skier pressure study used six internationally certified Canadian ski instructors.
  • The 2012 skate study used five competitive skaters.

The 1998 study with the six internationally certified Canadian ski instructors provided Peak Force data that I could use to compare to the Peak Force data obtained from the 2012 skate study.

As I pointed out in my previous posts, skating and skiing are similar in that they both depend on the ability of the participant’s neuromotor system to create a foundation of dynamic stability across the skate blade or the inside edge of the outside ski prior to being able to effectively apply force to the ice blade or ski edge. The existence of dynamic stability across the skate blade or inside edge of the outside ski enables the neuromotor system to regulate fore-aft stability in what is typically referred to as skater or skier balance.

Peak Force

Peak Force is the highest force applied in an Impulse Force

In the skate study skaters performed forward skating sprint starts in each skate (OS and NS) for a total of 6 trials each. As would be expected with competitive skaters Dynamic Stability as represented by Peak Force was very close among the skaters in their Own Skates as shown in the graphic below.

But when the highest and lowest Peak Forces of the competitive skaters were compared to the highest and lowest Peak Force of the internationally certified Canadian ski instructors the difference was much greater; approximately 125% for the skaters and 300% for the ski instructors. The researchers noted this significant variance and suggested equipment could have been a factor. But that aspect was not investigated.

Peak Force Improvement

It would seem logical to assign sole responsibility for such marked differences to inferior muscle strength or improper training. Muscle strength and training are definitely important factors. But their contribution to overall performance is dependent on the ability of a competitor to create dynamic stability and quickly acquire a position from which they can effectively apply force to a skate blade or edges of a ski. These factors, in turn, are dependent on a functional environment in the footwear for the physiogic function of the lower limb.

As shown in the graphic below, when the same skaters switched from their Own Skates (OS) to the skates I prepared (NS) there was an immediate and statistically significant improvement in mean Peak Force of approximately 190%. Even more significant is the fact that the Peak Force of skater number 4 (the lowest of the four skaters) increased by approximately 252% changing the skater’s ranking from #4 to #1.

Impulse Force Improvement

An Impulse Force is a high force of short duration that causes a change in momentum.

When the skaters switched from their Own Skates (OS) to the New Skates (NS) there was an immediate mean increase in Impulse Force of approximately 216% as shown in the graphic below. Even more significant, the Impulse Force of skater number 4 (the lowest of the four skaters in their Own Skates) increased by approximately 276% raising skater number 4 to almost the same level as skater number 3. Meanwhile, an increase in Impulse Force of approximately 224% raised skater number 2 to almost the same level as skater number 1. In other words, the New Skate was literally a game changer that resulted in a leveler playing field for the four competitive skaters.

Center of Force (CoF) Variance: Where Races are Really Won

The most significant effect of the New Skate (NS) was on what is called Center of Force (CoF) Variance. Center of Force Variance is the amount of forward movement of the Center of Force within a fixed unit of time to the position on a skate blade or ski edge where force can effectively be applied.

The graphic below shows the Center of Force Variance of the four competitive skaters in their own skates (OS).

The graphic below shows the Center of Force Variance of the four competitive skaters in their Own Skates (OS) compared to the Center of Force Variance in the new skates (NS). When the skaters switched from their Own Skates (OS) to the New Skates (NS) there was an immediate mean increase in CoF Variance of approximately 172% as shown in the graphic below. Skater number 4 experienced the largest increase in CoF Variance (approximately 241%) that changed the ranking from #3 to #1.

An increase in the variance of CoF results in increased control during the stance phase of forward skating.

The graphic below shows what would happen if only skater number four were provided with New Skates (NS) while the other 3 competitive skaters continued to use their Own Skates (OS). Think of the red dashed line at 1.20 as the finish line of the CoF Variance race. It should obvious who will win and who will have the advantage at every turn.

The Score for Skater Four

Skater number four experienced the following improvements in the New Skates (NS) over their Own Skates (OS)

  • Peak Force – 252%
  • Impulse – 276%
  • CoF Variance – 241%
  • Mean improvement – 256%

The improvement in the three metrics was immediate and, based on my experience with skiers and racers, probably immediately reversible simply by having the competitive skaters revert to their Own Skate (OS) format.

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. (2.)

To paraphrase Dr. Emily Splichal:

A skier is only as strong as they are dynamically stable.

In my next post, I will discuss the implications of the skate study and associated performance technology and metrics for the future of skiing, especially ski racing.


  1. A Novel Protocol for Assessing Skating Performance in Ice Hockey – Kendall M, Zanetti K, & Hoshizaki TB – School of Human Kinetics, University of Ottawa. Ottawa, Canada
  2. 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

WHY TRYING TO COPY HIRSCHER AND SHIFFRIN’S MOVES DOESN’T WORK – PART 3

Superior Dynamic Stability (Equilibrium) has always been the single most important factor responsible for the dominance of the World’s best skiers. It enables racers like Hirscher and Shiffrin to literally free fall, maximally accelerate under gravity then precisely land on and lock up the edges of their outside ski, establish a line and project their body towards the next gate in milliseconds and initiate a new free fall. Maximization of Dynamic Stability is crucial for a skier to set up a dynamically stable foundation in the outside ski to stand and balance on so they can establish the strongest possible position from which to generate the internal forces required to oppose the external forces acting on them.

Both skating and skiing are susceptible transverse instability manifesting as wobble oscillation (chatter) across the pivot formed by the skate blade or inside edge of a ski underfoot that challenges skater/skier Dynamic Stability. A number of quantifiable metrics are reliable indicators of the presence and degree of Dynamic Stability.  A key metric is Peak (maximum) Force.

The graph below shows the peak forces of 4 competitive skaters in the 2012 University of Ottawa skate study in their own skates (OS) and the skates I prepared (NS).I have added green bars for the elite skiers with highest and lowest peak forces from the 1998 University of Ottawa pressure study for comparison purposes.

Of interest is the fact that the peak force of one of the elite ski instructors is almost 3 times the peak force of one of the other elite ski instructors.  Given the small variances in peak Forces of the 4 competitive skaters in their own skates and the significant increase in peak Force seen in the skates I prepared (NS) it is reasonable to assume that some factor or factors are limiting the performance of the competitive skaters and one or more of the elite ski instructors in the 1998 study. The researchers recognized this in the 1998 ski pressure study (1.)

A factor that was not controlled during data collection was the equipment worn by the subjects. The skiers wore different boots, and used different skis, although two of them had the same brand and model of skis and boots. It still has yet to be determined if that factor had any effect on the results. A point that all the skis that the subjects used had in common is that the skis were all sharp side-cut skis (also called shaped skis). Another equipment variation which may have affected in-boot measurements, is that some subjects (n=5) wore custom designed footbeds, while the other did not. 

A 2017 pressure study on giant slalom turns (3.) notes several limitations to the use of pressure analysis technology fit to ski boots to record pressures during skiing.

The compressive force is underestimated from 21% to 54% compared to a force platform, and this underestimation varies depending on the phase of the turn, the skier’s skill level, the pitch of the slope and the skiing mode. 

The use of the term underestimated is out of context. When fit to a ski boot, pressure analysis technology records the plantar pressures imposed on the pressure insole. The researchers clarify this with the statement:

It has been stated this underestimation originates from a significant part of the force actually being transferred through the ski boot’s cuff.

In other words, interference with the application of plantar pressure by the structures of the ski boot is negatively affecting the ability of skier to create a foundation characterized by Dynamic Stability under the outside foot of a turn.

As a result, the CoP trajectory also tends to be underestimated along both the anterior-posterior (A-P) and medial-lateral (M-L) axes compared to force platforms.

As I will show in my next post, CoP trajectory is limited by the structures of a skate or ski boot, not underestimated by the pressure analysis technology which is only the messenger in the scheme of things.

Although a static physical environment is not the same as the dynamic physical environment associated with skating or skiing, pressure data captured on a force platform in a controlled laboratory setting can provide valuable baseline data on L-R symmetry that could explain the asymmetry seen in the large differences in the 1998 ski pressure study (1.) as shown in the table below.

What the pressure data is really showing is a L-R imbalance of Dynamic Stability.

Australian therapist and skier, Tom Gellie, posted on L-R pressure asymmetry on September 30 2018 on his FaceBook page, Functional Body.

Dynamic equilibrium is the most important aspect of skiing. Everything else is subordinated. Every aspect of skiing from equipment to technique should be assessed on its impact on the processes of Dynamic equilibrium. Ski design in particular needs to be analyzed especially as it pertains to sidecut geometry since it dictates the point where ground reaction force occurs and ground reaction force is fundamental to the initiation and maintenance of the processes of Dynamic equilibrium.

– M. Mester: keynote speaker at the first annual science symposium on skiing

……. to be continued in Part 4.


  1. ANALYSIS OF THE DISTRIBUTION OF PRESSURES UNDER THE FEET OF ELITE ALPINE SKI INSTRUCTORS – Dany Lafontaine, M.Sc.1,2,3, Mario Lamontagne, Ph.D., Daniel Dupuis, M.Sc.1,2, Binta Diallo, B.Sc.: Faculty of Health Sciences1, School of Human Kinetics, Department of Cellular and Molecular Medicine, Anatomy program, University of Ottawa, Ottawa, Ontario, Canada – 1998
  2. ANALYSIS OF THE DISTRIBUTION OF PRESSURE UNDER THE FEET OF ELITE ALPINE SKI INSTRUCTORS – Dany Lafontaine, Mario Lamontagne, Daniel Dupuis, Binta Diallo, University of Ottawa, Ottawa, Ontario, Canada – 1998
  3. Influence of slope steepness, foot position and turn phase on plantar pressure distribution during giant slalom alpine ski racing: Thomas Falda-Buscaiot , Frédérique Hintzy, Patrice Rougier, Patrick Lacouture, Nicolas Coulmy – Published: May 4, 2017 https://doi.org/10.1371/journal.pone.0176975

 

WHY TRYING TO COPY HIRSCHER AND SHIFFRIN’S MOVES DOESN’T WORK – PART 2

In previous posts I discussed the two studies (1, 2) done by the University of Ottawa in 1998 that analyzed pressure under the feet of elite alpine ski instructors

The pressure data from the study that used 6 elite alpine ski instructors found maximal (peak) force ranged from a high of 1454 Newtons to a low of 522 Newtons. The graph below compares the peak force seen in pressure data captured from the 4 competitive skaters in their own skates from my last post to the highest and lowest peak force seen in pressure data captured from the 6 elite alpine ski instructors used in the 1998 University of Ottawa study.

In consideration of the fact that the researchers commented that force-time histories revealed that forces of up to 3 times body weight can be attained during high performance recreational skiing it is interesting that the peak force of one of the 6 elite alpine ski instructors in the study was less than the lowest peak force of one of the 4 competitive skaters in the 2012 University of Ottawa study while the highest peak force of one of the 6 elite alpine ski instructors in the 1998 study was almost twice the highest peak force of one of the 4 competitive skaters in the 2012 University of Ottawa study.

A significant challenge in attempting to conduct foot pressure studies with alpine skiers is the variability of the slope and environmental and piste conditions. Test conditions and variables, especially ice, can be tightly controlled in the conditioned environment of an indoor skating rink.

Although the studies did not provide pressure data that compared peak and average pressures for different ski instructors, the peak forces from one study reached up to 30 newtons per square centimetre.

In the spring of 2012 I was asked to modify a number of pairs of the same brand and model of a hockey skate for use in a study that would compare metrics derived from pressure data captured from a competitive skater’s own skates to the same metrics from data acquired  from skates I had modified. I saw this as an opportunity to document the effect of modifications made to hockey skates based on the principles of neurobiomechanics described in my patents and this blog. When I speculated that the metrics derived from the pressure data might show improvements as high as 10% (i.e. 110%) I was told that the study was unlikely to result in more than a single digit improvement of approximately 2% or 3%.

I modified the pairs of skates in the shop in the garage of my home near Vancouver. The modifications were general in nature and made without the benefit of data on the feet of the test subjects. No modifications were made after I shipped the hockey skates to the University of Ottawa. I was not involved in the design of the study protocol or the actual study. I was hopeful that the study would produce meaningful results because it would have implications that could be extrapolated to alpine skiing.

The graph below shows the highest peak force in Newtons recorded for each of the 4 competitive skaters in their own hockey skates (blue = OS) and in the hockey skates that I modified (red = NS). The improvement was immediate with little or no run in period in which to adapt. The percentage improvement for each skater is shown at the top of each bar.

The mean (i.e. average) improvement was approximately 190%. The only factor that improvements of this magnitude could be attributed to is improved dynamic stability resulting from an improved functional environment in the skate for the foot and leg of the user.

……. to be continued in Part 3.


  1.  ANALYSIS OF THE DISTRIBUTION OF PRESSURES UNDER THE FEET OF ELITE ALPINE SKI INSTRUCTORS – Dany Lafontaine, M.Sc.1,2,3, Mario Lamontagne, Ph.D., Daniel Dupuis, M.Sc.1,2, Binta Diallo, B.Sc.: Faculty of Health Sciences1, School of Human Kinetics, Department of Cellular and Molecular Medicine, Anatomy program, University of Ottawa, Ottawa, Ontario, Canada.
  2. ANALYSIS OF THE DISTRIBUTION OF PRESSURE UNDER THE FEET OF ELITE ALPINE SKI INSTRUCTORS – Dany Lafontaine, Mario Lamontagne, Daniel Dupuis, Binta Diallo, University of Ottawa, Ottawa, Ontario, Canada

WHAT’S YOUR PQ? [PERFORMANCE QUOTIENT]

After my disastrous experience in 1977 with the mythical Perfect Fit with Crazy Canuck, Dave Murray (.1); one that transformed Mur from a World Cup racer to a struggling beginner, my work on ski boots became focussed on removing instead of adding material and making room to allow a skier’s foot to assume its natural configuration in the shell of the ski boot. As I improved the accommodation of a skiers’ neurobiomechanical functional requirements in the ski boot, skier performance improved in lockstep. I was merely reducing the structures of the boot that interfered with performance to enable a skier/racer to use the performance they already had.

Fit: The Antithesis of Human Function

Fit, by it’s definition of joining or causing to join together two or more elements so as to form a whole, is the antithesis (def: the direct opposite) of enabling the function of the human foot and lower limbs as one of the most dynamic organs in the human body. Fitting a ski boot to the foot and leg of a skier, especially a racer, equates with imposing a disability on them (2.). Although I didn’t realize it until I read The Shoe in Sport and learned of the barefoot studies done at the Human Performance Laboratory at the University of Calgary, my work on ski boots had transitioned from Fitting (disabling), by adding materials to liners to fill voids between the foot and leg and shell wall, to UnFitting (abling) by removing materials from liners and expanding and grinding boot shells so as to accommodate the neurobiomechanical functional requirements of the foot and leg of a skier.

But the big breakthrough for me came when Steve Podborksi won the 1981-81 World Cup Downhill title using the dorsal constraint system (Dorthotic) I developed and later patented. The Lange boot shells the device was used in had the least constraint of any ski boot I had ever worked with. The instantaneous quantum leap in Steve’s performance compared to the same shell using a conventional liner raised the question of how could a skier’s maximum performance be achieved and was there a way to compare to a skier’s performance in different ski boot/liner configurations to an optimal reference standard?

A reliable indicator that my un-fitting was trending in the right direction was that skiers consistently found that skiing became easier. For racers, coaches would typically report that the racer was skiing better. Improved race results served as further confirmation of my efforts. But these indicators were subjective. I wanted a way to not just measure performance with quantifiable metrics generated from data specific to the activity, I wanted to be able to compare the same metrics to a reference or baseline standard that represented the optimal performance of a skier or racer at a given moment in time. Without a way to measure and compare performance there is no way of knowing how a ski boot is affecting a skier or racer and especially no way of knowing how close they are to skiing at their maximum level of performance. I wanted to develop a skier Performance Quotient or PQ.

Definition of Quotient

  • Mathematics: – a result obtained by dividing one quantity by another.
  • a degree or amount of a specified quality or characteristic.

A skier Performance Quotient would capture baseline metrics from a skier’s performance in a ski boot that provides the optimal functional environment for the foot and lower limbs to the skier’s peformance in different ski boots including a skier’s current ski boot. The ski boot that provides the optimal functional environment for the foot and lower limbs would be designated as 100%. If the same metrics captured in a different ski boot were 78% of the reference standard, the skier’s PQ in the ski boot would represent a PQ of 78% against a possible 100% or 78/100.

Raising the bar of skier/racer function with body work and/or conditioning will raise the PQ. But it cannot close the PQ gap created by the performance limitations of the interference with neurobiomechanical function caused by their ski boot. Nor can trying harder or training more intensely overcome the limitations of a ski boot. Assuming 2 ski racers of equal athletic ability and mental strength, the racer with the ski boot that enables a higher PQ will dominate in competition. The only way to improve a skier’s PQ when it is less than 100% is to improve the functional environment of the ski boot.

In current ski boot design process, manufacturing and aesthetic considerations override skier functional requirements. An innovative approach to the design of the ski boot is needed. This is the subject of my next post.


  1. IN THE BEGINNING: HOW I GOT STARTED IN SKI BOOT MODIFICATIONS, May 12, 2013 – https://wp.me/p3vZhu-y
  2. LESS REALLY IS MORE, May 13, 2013 – https://wp.me/p3vZhu-N

 

WHAT SHOULD A SKI BOOT DO?

After Steve Podborski won the 1981-82 World Cup Downhill title using a revolutionary dorsal fit technology I developed for his ski boots in June of 1980, he proposed that we become partners in a venture to develop a new ski boot that would do for every skier what the dorsal fit system had done for him. In exchange for my creative efforts, Podborski would fund the venture up to a point after which we would try to raise funds from investors for the project.

If I accepted Podborski’s proposal (which I eventually did), I knew the we faced significant hurdles. After giving the proposal a lot of thought, I accepted Steve’s offer. Steve and I became partners in a company called MACPOD Enterprises Ltd. While I had identified some of the pieces of the puzzle, I didn’t yet know the answer to the question what a ski boot should do. But I knew that when the time came to raise money I would need to provide investors with convincing evidence that I knew the answer to this question.

Podborski’s success lent credibility to the project. But his credibility was based on his subjective assessment supported by his race results. To be credible, a ski boot design based on principles of science would need to be supported with data from actual skiing maneuvers that could generate meaningful, quantifiable metrics for such things as balance and ski control. When the metrics were compared to the same metrics from data captured from the same skiers using conventional ski boots, they would need to unequivocally demonstrate superior performance of the MACPOD ski boot. I had to come up with a format that would satisfy potential investors that the new ski boot MACPOD would develop would be at least as good, if not better, than the system Podborski used to win the 1981-81 World Cup Downhill title. Whatever format I came up with had to be capable of allowing investors who skied to ski in it.

In 1992, MACPOD raised money from investors to fund the first phase of the venture. The pressure was on.

The single variable assessment protocol

The factor that convinced Podborski of the merits of my dorsal fit system was the comparison test he did against identical Lange boot shells fit with conventional Lange liners.

After rupturing his ACL testing skis at the end of July in 1980 Steve went to France 2 weeks before the opening downhill race of the 1980-81 World Cup season at Val d’isere to be with the team to support them. He had not planned on skiing, let alone racing, because he had been told by his doctors he was out of commission for the 1980-81 World Cup Downhill season. But Podborski had brought 2 pair of identical Lange boot shells to France with him just in case. One pair had the untested dorsal fit system with only the upper cuff of a Lange liner mounted on the boot shaft. The other pair had conventional Lange liners.  The only difference between the boots was the fit system; the classic single variable assessment protocol.

The graphic below from my US Patent shows a conventional tongue format (20) in FIG 3 (prior art) compared to my dorsal fit system (30) in FIG 5. The shin component (31) is like a conventional tongue.

On a whim, Podborski decided to see if he could ski in the boots with the dorsal fit system. He was amazed to find that he could ski well with little pain in his partially healed, reconstructed ACL. But when he tried to ski in the boots with the conventional liner he could barely ski.  I found this interesting because the impetus for the new fit system was my hypothesis that dorsal loading of the bones of the midfoot might reduce strain on the knee by dampening decompression of the arches resulting from perturbations in ground reaction force due to asperities and undulating terrain. A conventional liner could not be used because it would have interfered with the interface of the lower shell overlap closure on the upper surface of the dorsal fit system required to apply force to it. Fig 9 below from the patent shows how the overlap of the shell applies force to the upper surface of the dorsal fit system. The buckle closures allow the force, which should be minimal, to be regulated.

The ability to compare the dorsal fit system against a conventional liner system on the same day and in same conditions made the superiority of the dorsal fit system apparent. The unprecedented improvement in performance with no run-in period or special training program strongly suggested that the improvement resulted from reducing factors in conventional ski boots that limit or degrade human performance. This experience caused me to undertake a critical analysis of the functional requirements of the human system for skiing. This exercise opened the door to the possibility of technologies that would integrate external appendages such as skis and skate blades with the human system, what I later came to term Bio-Integration.

Bio-Engineering

If structures of ski boots, ice skates and cycling shoes can limit or degrade the human performance of the user it also became apparent to me that it might be possible to modify the function of the feet and lower limbs that would make it specific to activities such as skiing, skating or cycling and even potentiate neuromuscular function. I termed this concept Bio-Engineering. I didn’t realize until 1991 that the dorsal fit system used principles of Bio-Engineering.

The graphic below is the pressure image of the right foot of an elite cyclist showing the forces applied by the foot to the sole of the shoe on the pedal spindle at 3 o’clock in the stroke sequence at a low cadence with a moderate to high load on the crank. The cyclist is wearing a conventional rigid sole cycling shoe with no arch supports, wedges or other accessories.

Red is highest force. Dark blue is the lowest force. Forces were recorded with a Tekscan F Scan system fit to the shoe.

The highest force is applied under the ball of the great toe and the great toe and to a lesser extent, the second, third and fourth toes. The dashed line shows the approximate location of the pedal spindle which is the source of resistance/reaction  force. This pressure pattern is typical of elite cyclists. Ideally, the highest force should be applied across the width of the pedal spindle by the heads of all five metatarsals. Note that aside from the high pressure patterns on the ball of the foot and toes 1 through 4 the pattern is diffuse across the heads of metatarsals 2 through 5 and under the heel.


In my next post, I will show a pressure pattern of the same foot in the same position with a technology that Bio Engineers the foot and lower limbs and discuss the significant differences.

IS ‘SUBTALAR NEUTRAL’ SKIINGS’ HOUSE OF CARDS?

If you purchased custom footbeds for your ski boots or had your ski boots custom fit you may have been told that your foot was placed in subtalar neutral and that this created the strongest position of the bones of the foot and leg for skiing. Neutral in this context refers to a neutral configuration of the subtalar joint of the ankle/foot complex.

As best I can recall, the term subtalar neutral began to emerge in the ski industry about 1978. The authoritarian manner in which it was presented and promoted suggested that it was science-based and supported with evidence that conclusively demonstrated superior performance. But I never saw or heard any explanation as to how subtalar neutral could create the strongest position for skiing of the bones of the foot and leg and I have still not seen such an explanation.

Back in 1978, I didn’t even know what the subtalar joint was. I couldn’t envision how the bones of the foot and leg could be maintained in a specific configuration while foam was injected into a liner around the foot and leg or through some other custom fit system. But in spite of the lack of even a theory to support the premise of subtalar neutral as creating ideal biomechanical alignment of the bones of the foot and leg for skiing the premise seemed to be readily accepted as fact and quickly became mainstream. By the time The Shoe in Sport (which questioned the principles on which the plastic ski boot is based) was published in 1989 (1987 in German), neutral subtalar was firmly entrenched in the narrative of skiing.

In my US Patent 4,534,122 (filed on December 1, 2013) for a dorsal support system that I called the Dorthotic, I had unkowingly tried to fix the subtalar joint in a static position as evidenced by the excerpt below from the patent:

The system of the invention applies significant pressure to the dorsal (upper) surface of the foot over the instep, including the medial and lateral aspects thereof, and hence to the bones of the mid-foot to substantially prevent these bones from moving relative to each other.

Note: The prior art refers to the current paradigm in existence.

The objective of the dorsal support system was to immobilize the joints of the bones below the ankle in conjunction with the joints of the bones of the midfoot while allowing unrestricted dorsi-plantarflexion of the ankle joint within it’s normal range of motion. But the significant medial (inner) pressure applied by the  system to the bones of Podborski’s foot below his ankle made it difficult for him to stand and balance on one foot with the system in a ski boot shell even on the concrete floor of my workshop. Removing the offending structure from the dorsal support system quickly resolved the issue by allowing his foot to pronate. This made me aware that structures that impede supination did not appear to create issues. This insight raised the possibility of a fit system based on selective constraint applied to specific aspects of the foot and leg as opposed to what I termed indiscriminate (general) constraint.

Even though at the time that I wrote my US Patent No, 5,265,350 in February of 1992 I still did not comprehend the mechanism behind the claimed superior performance associated subtalar neutral, I knew enough to know that attempting to fix the subtalar joint in any configuration in a ski boot would interfere with, or even prevent, a skier from balancing on one foot.

Here is what I said in the patent:

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 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 (balance on one foot on the outside ski).

I later discovered that the above statement came close to the truth.

I also discussed the issue of subtalar neutral in my post NO NEUTRAL GROUND (2.) published on September 1, 2014. But I did not learn about the origins of subtatar neutral and especially the intense controversy surrounding it in professional circles until recently when I came across a discussion on Root and his subtalar neutral theory in an online podiatry forum.

The Origin of Subtalar Neutral

Merton’s Root’s subtalar joint neutral theory was first described in the textbooks, Biomechanical Examination of the Foot, Volume 1. – 1971 (Root, Orien, Weed and Hughes) and Normal and Abnormal Function of the Foot – 1977 (Root, Orien, Weed). The basic premise of Root’s subtalar neutral theory is that a neutral position of the subtalar joint (which Root defined as existing when the foot was neither supinated or pronated), is the ideal position of function in static (two-footed bipedal, erect) stance and in gait where the subtalar neutral theory posited that the foot was pronated in the first half of the stance phase then transitioned through neutral in mid stance to become supinated in the latter half of the stance phase.

Root’s paradigm proposes that the human foot functions ideally around the subtalar joint’s neutral position and that deviations from this ideal position are deformities.

What Root really said

Root and his associates never stated that the joints of the foot should be immobilized in subtalar neutral. The reference to static in subtalar neutral as the ideal position of function in static stance pertained to a subject standing in place in an erect bipedal stance on a flat, level, stable surface with the weight apportioned between the two feet. In this static stance the Root subtalar neutral theory posited that the subtalar joint should rest in neutral. Root and his associates never stated, implied or suggested that the joints of the foot should be configured and immobilized in subtalar neutral. Further, Root and his associates made no reference, of which I am aware, to the application of subtalar neutral to activities other than static stance and gait. Critrics have asserted that a subtalar neutral position in static stance is neither normal or ideal. In defining subtalar joint neutral as normal, Root’s theory implied the existence of abnormal pathologies in the feet of the majority of the world’s population.

The lack of evidence

Critics of Root and his associates “Eight Biophysical Criteria for Normalcy” claim the criteria was nothing more than hunches, that these conjectures were accepted as fact, when, in reality, there was no experimental data or research to support them and that the eight criteria were neither normal or ideal.

 The STJ neutral position problem

One of the early critics of Root and his associates was Kevin Kirby, DPM. He is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt College in Oakland, Ca.

Kirby observed a large error range in determining STJ neutral position on the same foot from one examiner to another. In unpublished studies done during his Biomechanics Fellowship at the California College of Podiatric Medicine, Kirby found that the Biomechanics Professors were +/- 2 degrees (a 4 degree spread) and the podiatry students were +/- 5 degrees (a 10 degree spread)  in determining STJ neutral position.

Subtalar neutral appears to be what amounts to a knife edge between pronation and supination where neutral is the border or transition point between the two states. Unless the subtalar neutral position can be precisely and consistently identified, it is impossible to know whether the subtalar joint is pronated or supinated.

The future of subtalar neutral in skiing

Too many times theories of how the human foot functions and therefore how mechanically inducted foot problems are treated have been presented as if they were facts. The dogmatic adherence that sometimes ensues from such an approach has frequently stifled the evolution of foot mechanics. This has been particularly apparent in the field of podiatry which has been dominated by the Root paradigm. (4.)

The long standing controversy and growing challenges mounted against the credibily of Root’s subtalar neutral theory has significant implications for the continued promotion of subtalar neutral in skiing as providing the strongest position of the bones of the foot and leg.

It may eventually be shown to be unfortunate that Root’s influential textbooks were published at a time when the ski industry was attempting to come to terms with the skier/boot interface issues associated with the new paradigm created by the rigid shell plastic ski boot.

In my next post, I will discuss what a ski boot should do for the user or perhaps, more a case of what a ski boot shouldn’t do.


  1. Root ML, Orien WP, Weed JH, RJ Hughes: Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971
  2. https://wp.me/p3vZhu-Bv
  3. Are Root Biomechanics Dying: Podiatry Today, March 27, 2009
  4. Foot biomechanics- emerging paradigms: Stephen F Albert, 4th Congress of the International Foot and Ankle Biomechanics (i-FAB) Community Busan, Korea. 8-11 April 2014

 

IN THE BEGINNING: HOW I GOT STARTED IN SKI BOOT MODIFICATIONS

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 thinking 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.).

Conclusions
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).


  1. https://wp.me/p3vZhu-UB
  2. https://jfootankleres.biomedcentral.com/articles/10.1186/s13047-017-0189-2