WHY HIRSCHER AND SHIFFRIN CAN CROSS THE LINE

There has been a huge surge in interest in my post HIRSCHER AND SHIFFRIN WIN BY CROSSING THE LINE.

The reason Hirscher and Shiffrin can ski this way is that they have the ability to cross the rise line and establish balance on their outside foot and leg in milliseconds. This enables them to make what amounts to a hairpin turn. They are on and off their edges like a flat stone skipping off the water. The reason they can do what few other racers can is because their boot setup supports the requisite neurobiomechanics. I discuss this in my last post WHY HIRSCHER AND SHIFFRIN ARE DOMINATING.

WHY SHIFFRIN AND HIRSCHER ARE DOMINATING

Existing footwear does not provide for the dynamic nature of the architecture of the foot by providing a fit system with dynamic and predictable qualities to substantially match those of the foot and lower leg.

MacPhail, US Patent 5,265,350 – November 30, 1993

Of all the figures who have influenced the development of the plastic shell ski boot over the years, the Australian, Sven Coomer, stands tall as one of the most significant and innovative. More recently, Coomer was involved with the development of Atomic’s race boot, the Redster, used by Marcel Hirscher and Mikaela Shiffrin. Coomer claims that the Redster allows the skier’s forefoot to flex and move naturally within the confines of the shell.

A 2014 article by Jackson Hogen quoted Coomer as saying:

This liberation of the previously stunted, frozen and crushed forefoot is what allows for the subtle edging and foot steering that initiates the slalom turns of World Cup champions Marcel Hirscher and Mikaela Shiffrin. (1.)

Four years, later Hirscher and Shiffrin are dominating the technical disciplines of the World Cup circuit.

The ability to establish balance on the outside foot and ski in milliseconds is dependent on the ability of the forefoot to fully spread and acquire fascial tensioning that extends to the ankle and knee. This is called time-to-stabilization. Although Coomer doesn’t mention them, a myriad of other factors are also critical; including the alignment of the big toe on the long axis of the foot and the optimal ramp angle.

Coomer suspects that if racers would only fit their boots more accurately, coupled with a dynamic molding inner boot medium between the foot and shell, and without down-sizing into short, narrow, thick-sidewall shells, their results just might improve. (1.)

In order to realize their maximum potential it is critical that racers and even recreational skiers have a ski boot fit with dynamic and predictable qualities that substantially match those of the foot and lower leg. Yet Coomer readily acknowledges:

Many racers believe they need downsized, super-stiff, ultra-narrow boots. The most accomplished alpine ski boot designer of the plastic era, Sven Coomer, believes that’s changing.(1.)

But then, he seems to retract his optimism when he says that after forty-five years as the Cassandra of the ski boot world, he knows all too well that just because you can prove you’re right, it doesn’t mean your advice will be heeded.

My observation is that since Hogen’s 2014 article, the situation with downsized, hyper-restrictive ski boots that severely compromise the dynamic nature of the architecture of the foot, has gotten worse. I have seen instances where after having ski boots properly fit, it took several full seasons for the competence of the balance to be fully restored after a skier or racer’s feet and legs were constrained for years in ski boots that were too small and too tightly fit.

Marcel Hirscher and Mikaela Shiffrin have heeded Coomer’s advice. Others choose to ignore him at their own peril. In so doing, they handicap their efforts and limit their race results.

In my next post I will start a series of posts on how to build a ski boot from the snow up; one that provides a fit with dynamic and predictable qualities that substantially match those of the foot and lower leg.

  1. The Master Boot Laster by Jackson Hogen: The International Skiing History Association – Article Date: Tuesday, June 3, 2014

(NEURAL) BIO (MECHANICAL) ENGINEERING: DOES IT WORK?

The proof of a performance concept lies in the data. If neural bio mechanical engineering can improve human performance in a specific application such as skiing, skating or cycling then it should be possible to demonstrate meaningful performance improvement with quantifiable metrics generated from data captured from the actual activity. In the case of cycling, meaningful improvement would be shown by an increase in metrics such as peak force transferred to the pedal spindle that cannot be explained by other factors. In order to attribute any change in performance, whether positive or negative, to neural bio mechanical engineering the effect must be immediate, reversible and reproducible. In the case of the improvement seen with Podborski’s performance using ski boots fit with the dorsal fit system, reverting to identical boot shells fit with a conventional liner reversed the improvement in performance.

Where possible, standard protocols should be used and testing performed by experts in the field. In the case of the cycling shoe Tekscan F Scan data comparison, my only involvement was to analyze the human lower limb requirements for cycling and generate the design and specification for the device that produced the neural bio mechanical engineering effect. I played no role in designing the test protocol or conducting the tests. I was not even an observer.

So how did the neural bio mechanical engineering system work in the application to cycling?

Performance Metrics

There are numerous metrics that can be used to assess and compare performance. The subject test was limited to pressure analysis using the Tekscan F Scan system.

In the graphic below the upper image outlined in red is the F Scan pressure image of an elite cyclist captured at 3 o’clock in the crank cycle at moderate to high load using their own conventional cycling shoe. The F Scan pressure image outlined in green below the first image is of the same cyclist using the device that bio engineered the foot and lower limb.

Results

There are a number of significant differences between the forces applied with the same cyclist with the conventional cycling shoe and the bio-engineering. In the 2 F Scan images, the contact area of the application of force across the heads of the metatarsals over the pedal spindle with bio-engineering is much greater and the force much higher than the force applied to the heads of the metatarsals in the conventional shoe.

The two significant, quantifiable (measurable) metrics that relate directly to cycling performance are: Peak Force and Anterior-Posterior (forward-backward) Excursion of the Center of Force.

Peak Force

The peak (maximum) force with the device that bio-engineered the foot and lower limb was 140% of the peak force applied with the conventional cycling shoe.

Anterior-Posterior (fore-aft) Force Excursion

This is the range of forward-backward movement of center of force through the crank cycle.

The graphic below shows the tracking of center of force forward and backward in the pedal stroke. Notice how straight the force tracks in the lower image with bio engineering compared to the upper image captured from the conventional cycling shoe.

The ability to move the center of force forward and backward, not just down and, more important, substantially aligned with the crank rotation is both more consistent and efficient than the excursion tracking with the conventional shoe. The bio engineering device improved excursion by 175% in rearward tracking force (long bars) and 200% in forward tracking force (over the top) as shown by the short bars below the images.

In my next post I will discuss how I designed a ski boot from the snow up using principles of neural bio-mechanical engineering.

INTRODUCTION TO (NEURAL) BIO (MECHANICAL) ENGINEERING

Neural biomechanical engineering is an external, non-invasive, reversible process that alters the neuralbiomechanics of the human feet and lower limbs in a manner that makes their function specific to an activity such as skiing, skating or cycling. In some cases, the process can potentiate muscle power and/or the processes of balance. Neural biomechanical engineering is human function centric.

The graphic below is the pressure image of the right foot of the same elite cyclist in the last post except that the foot has undergone neural biomechanical engineering.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 primary forces are now across the heads of all five metatarsals with secondary forces under the big toe and, to a lesser extent, the second and third toes. The primary force is now applied to the pedal spindle. The applied force is also more focussed under the heel.

There are many other more subtle but important changes. But the central issue is whether metrics show a significant quantifiable improvement in performance.

What, if any, improvement in performance resulted from the application of neural biomechanical engineering? Any guesses?

 

 

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 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.).

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