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

 

6 comments

  1. I’ve never seen one but Sven promotes his zip fit liner as having an all neoprene(Spenco) forefoot which is actually quite flexible depending on the thickness. So it may be worth trying for Herb.
    I also think he was behind the Atomic Hawx design that put gill like cuts in the boot to allow some longitudinal flex. This was an interesting idea. I’m not sure what he was trying to achieve with this but I know It took me a long time and lots of work to ski as well in my Alpine boots as I could with my low plastic Telemark boots. I don’t know if he was trying to achieve a better flexing ski or activating the Windlass Mechanism. Interesting guy.

    1. I agree that Sven Coomer is a very interesting guy. He is also innovative. But I don’t know much about his early approach to ski boot design and fit. I tried contacting him but got no response. Back in the ’70s I was reworking Lange tricot (soft) liners to reconfgure the toe box and add a Spenco element. I would use the next size up liner then reconfigure the toe box. I will post on this at some point.

      Your story of taking a long time and lots of work to ski as well in your Alpine boots as you could in your Telemark boots is all too familiar. It has been my experience that it can take several years of concerted effort to get a boot to the point where they can be skied in. It’s as if the manufacturers are intentionally designing boots to make them impossible to ski in.

  2. Hi David,

    Thank you for the history and the reality of the origins of “orthotic insoles” or footbeds. It is very disconcerting that there were no properly designed and executed studies to back up Root’s concepts which were presented as practical guides for podiatrists who are ostensibly “doctors”. It would be interesting to know the source of the first footbed/orthotic and the justification behind it as well as the first ski boot orthotic. In reviewing printouts of your posts I just came across the title “Overpronation? Get Over It”, and the quote by Dr. Nigg. Very appropriate.

    Having had custom orthotics for many years going back to the early blue Superfeet custom cork (2 pairs) and shoe/work boot models (which were promoted by my employer) the overall impression I have is that they do not so much lock up the movement of the bones of the feet as restrict movement and seem to cause some disfunction by causing the foot to assume an unnatural position to conform to or avoid excessive pressure from the orthotic. Retraining myself to allow for more natural movement of feet and body since going “barefoot” about 8 years ago has been challenging. The most challenging part has, of course, been fitting ski boots to allow for proper functional movement inside the boot without having too much movement and lack of control of the skis.

    Are there some guidelines for where to stop expanding the shell or should I keep going until I can stand in monopedal stance and apply maximum pressure on the first metatarsal without impingement on my navicular or medial malleolus? At some point I assume I need to be able to apply pressure to the side of the boot shell and maybe cuff as well as the bottom. Should the cuff, then, be snug to the sides or just in contact with the lower shank while still allowing adequate fore/aft movement?

    I have been able to experience the walking sequence quite effectively while linking turns on easier terrain but, do not feel secure enough to apply it well to more challenging terrain. Any suggestions will be greatly appreciated as is all of the work on this blog.

    Thanks again,
    Herb Jones

    1. Hi Herb,

      Thank you for your comments. In all fairness to Root and the wrong direction that ski boot design went into when plastic boots emerged in the late 1960s, a quote from Benno Nigg’s book, ‘Biomechanics of Sports Shoes’ is appropriate.

      “In the early 1970s, biomechanical research on human locomotion was in its infancy and biomechanical studies of sports shoes were virtually non-existent.”

      The focus of Root and his associates in 1971 was on bones as forming the primary supporting structure for weight of the body. So from a simplistic perspective it made mechanical sense for the lower third of the leg and heel bone to be perpendicular to the ground and the subtalar joint to be in neutral. From the same simplistic perspective, supporting the arch was viewed as essential because the lowering of the arch due to compression-tension was perceived as the arch collapsing and failing. The problem is that these misperceptions became the cornerstones of the ski industry which is resistant to change.

      “…….the overall impression I have is that they do not so much lock up the movement of the bones of the feet as restrict movement and seem to cause some disfunction by causing the foot to assume an unnatural position to conform to or avoid excessive pressure from the orthotic.”

      That is a very accurate assessment of what I believe happens in situations where there is no pathology associated with a foot that by Roots’ standards would be assessed as pronated or supinated. Nigg goes into this aspect in his book.

      “Are there some guidelines for where to stop expanding the shell or should I keep going until I can stand in monopedal stance and apply maximum pressure on the first metatarsal without impingement on my navicular or medial malleolus? At some point I assume I need to be able to apply pressure to the side of the boot shell and maybe cuff as well as the bottom. Should the cuff, then, be snug to the sides or just in contact with the lower shank while still allowing adequate fore/aft movement?”

      In a series of future posts, I am going to attempt to address these issues in a systematic manner. The biggest problem I encounter in trying to work with skiers and racers (I don’t do much actual boot shell work any more) is liners that are next to imppossible to modify to create adequate width for the foot and correct alignment of the big toe which is crucial. In some cases it can take several ski seasons to get a pair of boots properly set up.

      Best regards,
      David

      1. Thank you David, for helping to put this in perspective. Last year , while searching for a better liner, I checked out the Zip fit liners which are appealing for the ability to add and remove the moldable filler material. I was curious about the guy doing the presentations on the Zip fit website, Sven Coomer, and found his bio which included being the major designer of the early Nordica ski boots and having developed a system of design criteria for plastic ski boots. I did not find the criteria,( 170+ in number I believe), but, it would be interesting to know what they are and how much has changed. Sven also started Superfeet, I believe, sold it and started Downunders footbeds (he’s Austrailian by birth) so he appears to be (still) in the prior art camp.
        The Zip Fit is an appealing idea but, it does not yet address the forefoot splay issue. I wonder if the industry cartel is still using Sven’s criteria for boot design.

        This past weekend I visited a bootfitter who I had worked with years ago and found him to be very willing to do what I want and not what he wants. He worked for Lange on the US race circuit. I am hopeful that he will be able to assist me in the more difficult phases, at least with the shells, which can require a lot of equipment to shape properly. He also was very helpful with suggestions on how to do things and did not hide what he was doing but, rather showed me how he was working. Very unlike the many shops which want to tell you what you need and fit boots the way they “know is right” much like the industry is making what they want and trying to convince us it is what we want and need.

        I apologize for being a bit impatient for more information on fitting but, I did not get much skiing in this season as I worked to get a boot that “works”. Once I proved to myself (this season) that this method works I became even more eager to make it work well. This is the second season of serious work to put your principles into practice and the most productive so far. I look forward to learning more about how to make my boots fit functionally and to your informative posts.

        Thanks again,

        Herb

      2. Hi Herb,

        Thankyou for doing the research on Sven Coomer. I found an article on Sven by Jackson Hogen called The Master Boot Laster (https://skiinghistory.org/news/master-boot-laster). Here’s Hogen’s opening statement:

        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.

        This is the concluding statement:

        The Redster race boot concentrates on stabilizing the rear foot with an ultra-solid spoiler so the skier’s forefoot is allowed to flex and move naturally within the confines of the shell. 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. 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.

        But then, Coomer, the Cassandra of the ski boot world for the last forty-five years, knows all too well that just because you can prove you’re right, doesn’t mean your advice will be heeded.

        If Coomer did indeed produce 170+ design criteria he would have published them. I checked the Downunders web site and there is still a reference to neutral.

        I will be publishing a new post soon that will set a new direction for The Skier’s Manifesto that will focus on functional requirements and options to achieve them in existing boots. I will also discuss my concepts of Bio-Engineering.

        The Zip Fit is an appealing idea but, it does not yet address the forefoot splay issue. I wonder if the industry cartel is still using Sven’s criteria for boot design.

        The ski industry has two impediments to advancing boot design as a science; 1) the DIN standard toe box shape makes it very difficult to allow the big toe to properly align and 2) they are stuck in neutral (subtalar)

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