The position of some in the ski industry is that the foot functions best in skiing when its joints are immobilized in a neutral position; ergo, when the foot is ‘captured’. Neutral in this context refers to a neutral configuration of the subtalar joint. The subtalar joint or STJ is the joint between the talus and calcaneus (talocalcaneal joint).  This important joint underlies the ankle joint (tibio-talar joint). It functions by allowing eversion and inversion of the foot.  When the STJ is in so-called neutral, the foot is neither supinated (inverted – sole turned inward), nor pronated (everted – sole turned outward). When viewed from the rear, the heel bone will appear to be vertical to the ground or supporting surface when the STJ is in neutral.

I have yet to find an explanation as to how immobilizing the foot in a neutral configuration, effectively rendering the lower limbs dysfunctional, would make the foot function best in skiing.  There are significant implications to not only preventing the foot from functionally pronating, but becoming functionally pronated very quickly.  I use the term “without delay” in reference to the ability of the foot to pronate in a timely manner within the confines of a ski boot.

At the initiation of the transition phase between turns, the center of the force applied to a ski by the inside foot of a turn will be under the proximate centre of the base of the heel bone. This is the default location of what will become known as the Centre of Pressure (CoP) at foot flat when force is applied to the snow by the heads of all five metatarsals and the base of the heel bone. In a ski with a width underfoot of 65-67 mm, the head of the first metatarsal of a size 9 US men’s foot will be substantially aligned above the inside edge of the outside ski. But the proximate centre of the force applied to the ski under the base of heel bone will be offset 30-35 mm to the outside turn aspect of the centre of the head of the first metatarsal (dimension X in sketch below). The fore/aft offset between the centers of the head of the first MT and the base of the heel bone will be approximately 60 mm (dimension Y in sketch below).

Centres of key pts

In the transition phase, the ski goes flat between edge changes.  At this time, CoP must be able to move from the base of the heel bone to the centre of the head of the first MT in a fraction of second through the mechanism of pronation (dashed red line).

COP excursion The kinematics is essentially the same as in the gait sequence: supination to pronation.  The unweighted swing foot is supinated:  the ankle is plantarflexed, the foot is inverted and the leg is externally rotated. The foot makes contact with the ground on its lateral border and everts about the STJ as the foot pronates. CoP moves forward in a sweeping arc towards the head of the first MT. When the head of the first MT is maximally loaded the skier is in monopedal function.

Monopedal function is a physiologic state wherein balance is achieved with the weight of the body borne on the medial plantar aspect of one foot. Foot pronation is the vital integral function of monopedal stance and is essential for balance and control in the sport of skiing

The ability to balance on one foot provides superior balance and control in sports such as skiing and skating.

Should CoP fail to complete the transitory shift to the head of the first metatarsal before the ski acquires a significant edge angle, an inversion moment arm will be set up that will cause the center of force to return to its default position on the centre axis of the foot and, by association, the centre axis of the ski. The resulting inversion moment of force across the STJ will be translated into an obligatory vertical axial moment of force that will rotate the leg as a unit externally; ergo, towards the outside of the turn.  In the scenario where a ski is on edge and external forces are at play that are pulling the COM of a skier towards the outside of a turn, there can be no neutral ground, no neutral STJ. There can only be eversion moments of force or inversion moments of force acting across the inside edge of the outside ski. The multi-axial joint system will do what it is designed to do: rotate simultaneously in 2 planes until the 3 points of the arch have made contact with a supportive surface and a stable source of ground reaction force has been acquired.

Whether this mechanism causes or contributes to injury is not conjecture. Any unbalanced moment of force across the STJ is a predisposition to injury of the lower limbs.


  1. I have been fitting ski boots for over 30 years, most of what is posted is over my head but I have a general understanding of what is going on. I have always been an advocate of “if you can’t flex your boots, you can’t turn your skis”. I work a lot with juniors both FIS and lower high school athletes, it’s the parents that insist that the child be in the stiffest race boots out there so as to have the best advantage to win. I continually struggle with parents to put proper equipment on the athlete. The attitude from the 70s prevail here. On a side note here, I am thoroughly enjoying the reading here.

    1. Hi Theron, glad you are enjoying my blog. The issue is not so much flexing the boots as being able to flex the ankles. Figure 56 of my US Patent 5,265,350 is sketch of a schematic of the resistance curve needed in a ski boot. There should be fore/aft free space within the boot cuff that allows about 12-14 degrees of low resistance ankle flexion. When the boot cuff or shank can actually rotate about the shell lower without distortion the resistance would be in the journals of the cuff. But the design of most boots relies on cuff distortion for ankle flexion. For this reason, I use a very stiff race shell with the cuff buckles closed in the first bale catch and no power strap. When I am skiing even in bumps I never have any sensation of cuff contact on any aspect of the cuff. I am not claiming there is never any contact. There has to be. But the large muscles in the back of my legs are absorbing the energy because they are in eccentric contraction. And I agree that boots today are not just so yesterday, they are so 70s.

      1. Matt,

        Please, don’t insult us by wilding guessing what HH thinks, does or dreams, about the foot, inside the boot, This is an example of knowing a little, about a great big expense of science.


        It’s center of knee mass (center point of the width of the knee), because it’s not the center of the knee cap, which far too many think is the center of their bootiverse 🙂

        Are you really suggesting there needs to be fore/after …space…,inside the ski boot, or do you really mean, there needs to a certain amount of dorsiflexion available? Do you care about the relationship of axis of the ankle hinge to the shell/cuff hinge point? What do you think is the most common reason a skier cannot flex their boots?

        Dr.Kim, Have you ever seen an exaggerated, internally rotated leg, with complaints of knee and ankle pain, and later came to learn, the skier has a flexible flatfoot (a large degree of STJ pronation, for everyone else), or 4-6 degrees of forefoot varus?

        Yes, there is a coupling, but in a loose pair of boots, or an excessively pronating foot, it’s a very loose, and hard to controlled, coupling. The foot reacts to GRF, if it pronates excessively then the talus not only moves medial, as the calcaneus everts, it plantar-grades. The medial malleolus sits on top of this wobbly platform, rocking and rolling medially. If this mess is not stabilized, no matter how far someone punches out the medial aspect of the shell and cuff, as Matt suggests HH thinks, the ankle will rock-right-to-it. All of this leads to a huge amount of internal rotation of the tibia, against the meniscus, and at the same time, pulls the hip forward. I don’t even want to talk about what all this does to the posterior tibial tendon and navicular.

        Do you believe a foot can excessively pronate, even if the skier has ankle equinus?

        I try not to be an enabler, I do not support old and invalid pseudo ski boot fit science. I don’t care what ski shop boot fitters did in the 70s.Today’s materials and designs are lightyears ahead of 70’s, 80s, and 90s, as is the science.

        I wonder if ski design has a place in this discussion, as it “feels” the GRFs, first? Is it important to anyone that what the ski feels is transferred to the plantar aspect of the foot —- the whole plantar aspect of the foot?

      2. Do you even read anything I write? Or are you in your own world? Your comment about boot cuff axis makes question whether you have a grasp of the basic principles of mechanics. Very few ski boot cuffs actually rotate on an axis. They are fixed to the lower and deform under load. Even if they did rotate about an axis, the glide path of the ankle is not a fixed arc and the proximate center is all over the map. This is not old news. It is ancient history. And how does an edged ski in a turn provide GRF under the whole foot? It is not possible. This is kindergarten level science. You seem to be claiming that the foot can be supported on air. What’s next? Walking on water?

      3. Skikinentics, I am sorry, but I have a far different perspective. Further, It would be nice if you let others answer, especially if they have more recent experience in boot fitting, and stance balance, if they do it

        I sure wish someone could point us to who started the notion that the STJ should be locked. This is one of those hand-me-down misconception. Early on, in our first discussions, you thought I was locking the STJ, just by making an orthotic!

        I also wish we could stick to real-world ski boot fitting, where 90% of all product is sold and where the average, or above average skier is not capable of overpowering a plug boot.

        You brashly state: “And how does an edged ski in a turn provide GRF under the whole foot? It is not possible.” You’re reading something into something I did not state!!! I did not say the GRF would be equal across the plantar of the whole foot!!!

        And,I AM THE LAST ONE TO SAY THE FOOT IS SUPPORTED BY AIR, Just the opposite!!

        Have you read anything I said? I have been a advocate for making custom insoles, or orthotics, as the starting point of custom bootfitting, since I started boot fitting, I know the biomechanics of the foot and lower extremity.I don’t have to guess, what is going on. I know, through my training, that the medial column of the foot is not an effective support, especially when doing side to side sports. This is as true for tennis players, as it is for skiers.

        Matt, yes, but which MTJ, and when?

      4. Robert, moments of force is kindergarten level science that a 2 year old who has been on a teeter-totter grasps. The principles of moments of force seem to be eluding you. The pivotal issue (pun intended) is the alignment or misalignment of COP and R in relation to the inside edge of the outside ski of a turn. It is laughable when you appear to suggest that the entire foot can be supported on an edged ski without COP residing under the head of the first MT and without an eversion moment of force. If this is not what you are suggesting, please elaborate. Until such time as you can present relevant data (as I have) that has been captured during actual ski maneuvers, your concepts are at best theories. The physical environment under which conclusions are made on a solid level surface with gravity as the sole external force acting on COM bears little resemblance to the dynamic, complex forces of skiing. The fundamental laws of the universe have not changed. Nor, is it likely that they are about to.

      5. To design a test mechanism, you have to fully understand what you need to test. You ignore GRF, across 100% of the surface of the foot, and you seem to promote the unsupported foot because some unidentified person, somewhere, once said the foot should be locked up, and you believe just the opposite, with ………… inbetween.

      6. This is what is escaping you. When the foot is on a ski that is on edge and R is pulling COM to the outside of a turn there is not automatically GRF under the entire ski. Only the inside edge and a portion of the base is in the snow; ergo GRF. The remainder of the base if the ski has air under it. Air is not GRF. But, its worse than that. The sidecut extends medial of the inside edge creating what amounts to an offset moment arm that will invert the ski unless opposed by an opposite force. Seriously Robert? This should be drop dead in your face obvious.

        BTW, I am following the knee because that is where the inversion moment of force ends up. When ski magazines boast that a ski boot maximizes ‘energy transfer’ what they are really saying is that the energy from perturbations in GRF is bypassing the foot and going straight to the knee. When knee injuries first emerged as a trend the comment was made, “We supported the ankle and were surprised to see knee injuries?” If you stiffen a link in the chain you send the force to the next link. This is as basic as it gets.

      7. Skikinetics, HOCKEY SKATES: Your informational biases about insoles, orthotics, and medial column support, gives you the wrong platform to evaluate hockey skate fit and performance. I have been making orthotics for figure, hockey and speed skates for 35 years. One has to have respect for biomechanics, and have working applicable experience, before designing a study. BTW, the “insole that comes with a boot or running shoes, etc, is called a sockliner.(industry term). You’re working with old science and old methods.

      8. Once again Robert, you are way off base. I supplied the skates for the study. I wasn’t part of the team that designed and conducted the study. I wasn’t even there. I was thousands of KM away. So I didn’t evaluate anything. One of the key researchers who did the study is the head of Tekscan Canada. His email address is on the poster paper. The other researcher, , has a string of degrees behind his name. Marshall Kendall was one of his students. Dr. Hoshizaki is an international authority on the biomechanics of skating. Please direct your comments to the parties that did the research.

      9. Robert you are not contributing anything to this conversation. The research team leader asked me to retrofit my technology to hockey skates for a study. I was not party to the study and I had no influence over the design or outcome just as I had no influence over the Birdcage research. The improvement in performance of my technology over that of a conventional skate was unprecedented and totally unexpected. The performance could have been worse than that of a conventional skate. I put my theories on the line. i was prepared to be proven wrong. I wasn’t. It’s time for you to move on.

      10. You’re right, I cannot contribute anything…… to someone who claims to own the subject. That door is closed. We should follow your lead, and assume, all is known, on your subject. You built a piece of test equipment. What didn’t it test for? There are all manner of pressure plates to measure GRFs on the plantar aspect of the foot. They are as good, as far as they go, but not perfect. Follow the knee.

      11. Robert, you said: “Please, don’t insult us by wilding guessing what HH thinks, does or dreams, about the foot, inside the boot, This is an example of knowing a little, about a great big expense of science”

        I don’t know why you feel insulted by my conjectures about HH. As I said I have read a lot of material from HH, including all his books, thousands of forum and blog posts and dozen of referenced “science” papers.

        I know that HH builds his insoles to give support, all I said was that I believe he allows for a bit more of pronation. I you have a different opinion about that you are very welcome to explain why. I am here to learn. Note also that I have not said that I think HH or David fits boots better than you do. No need to be defensive.

        Speaking of science, I am a man of science myself, although in a different field. If you have some science references that you think are relevant it would be much appreciated. As I said, I’m here to learn.

  2. Sorry Robert and all others for me not being very specific. I assumed everyone has read the same info I have from the beginning so my reference in going back 15 years was, had I allowed my ankles to flex from around1980 when the “dude”, I should have said the author “skikinetics,” was doing so with World Cup skiers, skiing would have been so much easier and enjoyable for me. The downside would have been that I would have lost out on valuable experiences that I have attained. A short version of my history is; a severe, non-skiing knee injury in 1974 left me unable to run. Fortunately I could still ski as long as I didn’t jump, straighten my leg, or get back seat. The first 2 items were easy but the back seat part, well, I lived in the back seat and it killed my knee. If I had simply been smart enough to unbuckle my ski boot cuffs all would have been fine. Instead, somewhere in the early part of this century I started to play with an adjustable plate that I can change the delta of the binding to change my fore/aft balance on the ski slope, which I have patented and have skied on now for over a decade. Got me out of the back seat, Now I can jump from one mogul to the next if I want with no stress on my knee. But being balanced fore/aft didn’t solve everything, I could never turn as well with my injured side as the other and finally I realized that one foot could invert/evert inside the boot and the other couldn’t; because the STJ was locked up. Making adjustments to the boots,the more I was able to move inside the boot, the easier skiing became and that much more fun. Skipping a lot of years and experiments in this diatribe, this past winter, after one major new discovery, I found that the looser I buckled my boots, the better everything became because I could flex my ankles!! It has been the most fun skiing has ever been (well since the day before at least!) so now I ski with the boot cuff and binding delta set so I can’t go back seat and my boots buckled just to the point where I hit the cuff just before my ankle hit their maximum flex. It’s literally the first time in my life I can actually carve and my boots aren’t even buckled, hardly. I balance on my feet and the boots are just kind of there, and for the first time in my life barely hindering my skiing!! AND I might add that if after testing this on some other skiers and it works as well for them, I’ll be able to say that the only thing right about the status quo of ski boots today is that the industry says there is a right boot and a left boot!!

    Then the icing on the cake was a good friend sent me the link to “” and this guy is explaining everything that I was experiencing this winter. So now instead of having to figure out everything myself I can try some of these boot modifications this coming year and have even more fun skiing “in spite of the ski boot!”

    1. That is very well explained, and should be easy for everyone to understand. Skiing with your boot buckled loosely, doesn’t help with binding release, though. What is the stiffness of your current boots? They’re not plug boots,are they? We used to do a drill with upper cuffs, unbuckled, but not any more, because of liability issues.

      1. Robert, I’m in a pair of Nordica, fairly high end but not plug/race stock boots about ten years old because I hated altering new $$$$ boots. They have a soft/hard mode in the back. I skied them with the buckles 2 notches tighter on soft mode in some of the ugliest icy bumps I’ve ever skied, very successfully. So successful that I was the only fool skiing them that day!!. But since it is all about experimenting and “the path” I figured I’d sacrifice my life for science and went to the hard mode with the cuff open to the point I previously (last post) described and skiing those terrible bumps was so much easier and actually a ton of fun. Forgot to say that I had to remove the power strap because it got in the way. I wasted $43 on Booster straps, I guess only to prove they get in the way too!! (I totally discovered the amount to loosen the cuffs by accident…long story) The problem is the release and safety issue is difficult for me to address honestly. My theory is to hit the front cuff of the rigid boot before my ankle is fully flexed. I haven’t fallen so I don’t know if it will work like I theorize. As a matter of fact, I can’t remember the last time I fell and lost a ski. In the 70s -90s (as a bump skier) I would buy race bindings and crank them to 14 and still pre-release. Ever since my adjustable plate and skiing in better balance my DIN is at 6 and I never come out of the bindings. The body can do amazing amounts of absorption, unless all the joints are locked up and one is out of balance, then one has to hope the bindings release before a joint does.

        Side note: have had the great fortune to watch a lot of gymnastics over the last few years. The best gymnasts are not just tiny. A lot of tiny gymnasts don’t do so well. Now you take a gymnast with flexible feet and ankles when barefoot, then size takes a back seat. A tiny gymnast with rigid feet can’t balance whereas a “big & stocky” gymnast with flexible feet can do incredible things.

        This is not a drill, cuffs unbuckled is the way I ski and the most “joyous” ever. I’m holding back on a couple of “minor” items that makes it work because the standard ski equipment doesn’t work as sold. If liability were a concern, no one would sole grind ski boots because that isn’t even scientific the way that it is being done. It’s not even elementary carpentry because most don’t level the whole sole, they take swipes off one edge and call it flat. Seen it with my own eyes!!. I can’t for the life of me figure out why sole grinding is “chic” and what Dave has done with boot cuffs has been hidden by the industry for decades.

      2. Michael, as I described in my post on the Birdcage experiments the scientist who prepared the protocols and over the actual tests (I was a spectator) did a series of experiments designed to study the effects of intervention of the muscles of the legs in dissipating perturbations in GRF (ergo, absorbing energy). What these experiments found was that limiting dorsiflexion of the ankle prevented muscles from intervening to absorb the energy. Here is a quote from the paper on balance by David Winter that I cited in my last post.

        “Tilting of the platform produced some interesting variations on the induced dorsiflexion and plantarflexions resulting from linear backward and forward translations of the platform. Tilting the platform upwards (at the toe end) stretched the gastrocnemii and a combined short latencygastrocnemii/hamstring response resulted. However, the upward tilt of the platform did not shift the body’s COM in the anterior direction (as did the backward translation), thus this response caused a backward sway of the COM that required a second response (185-250 ms) by the anterior muscles (tibialis anterior, rectus femoris) to prevent loss of balance. Further analysis of the initial responses revealed that the posterior anterior group of muscles turned on in a specific order. With additional lumbar muscles (erector spinae and abdominals) recorded there was a bottom-up sequence in the latencies. For a backward translation of the platform the gastrocnemii responded first, followed by the hamstrings, then the erector spinae. For a forward platform movement this sequence was tibialis anterior-rectus femoris-abdominals. Thus it appears the CNS recognizes the need to stabilize the joint closest to perturbation first, followed by the knee, hip, and spine.”

        Tests of this type are similar to the loads experienced in skiing moguls. However, the only balance studies ever done during actual ski maneuvers was my Birdcage studies done on the Whistler glacier in the summer of 1991. What we found with a series of experiments is that restricting the ability of the ankle to dorsiflex in what amounts to a rearward platform translation (ergo, a forward fall) shuts down the contraction of the muscles that modulate balance and protect the leg. This leaves the tibia unprotected against bending moments that can fracture it. Winter, “Thus it appears the CNS recognizes the need to stabilize the joint closest to perturbation first, followed by the knee, hip, and spine.” If the boot prevents the CNS from stabilizing the ankle and dissipating energy with muscles in the back of the leg, the energy must be absorbed by the fragile knee. This is kindergarten level science.

  3. Hello David,

    I am Morgan from france. What a such good website with very very interseting things.

    I am skier pasionate with a french blog on technique and more.

    I didn’t find your email and I have a question, sorry If it isn’t the place to ask this :

    Would you do agree that I traduce posts from your website ?
    Morgan : m(dot)petitniot@wanadoo(dot)fr


  4. Robert, what does STJ neutral mean to you in skiing? position neutral or force neutral?
    My point is that if you are balancing on the inside edge of the ski and the STJ is in normal “position” neutral the force will be to the inside of the STJ center, which means it is not really neutral in terms of the forces involved. If you instead pronate until the STJ center is aligned with the force you are force neutral but not position neutral.
    My simple view is that if the STJ center is outside the force vector an increase in force will cause eversion, reduced edge angle and eventually ski chatter.

    Regarding the knee. IMO, In an ideal setup the proper amount of pronation should lead to a knee position that is also on the force vector or slightly to the inside. Thus giving a good edge grip and low injury risk. This can be fine-tuned with orthoses, but not to a degree so that it restricts the necessary foot movements.

    Regarding the ski industry locking the foot in place. Isn’t the Fischer vacuum concept an example of that?

    1. Matt, you might want to rethink your statement: “My simple view is that if the STJ center is outside the force vector an increase in force will cause eversion, reduced edge angle and eventually ski chatter.” Eversion? Unless you are in some parallel universe where the anatomical references are polar opposite, I don’t think so.

      1. Seriously? What does outside knee mass have to do with postural responses and especially the balancing of moments of force across the joints of the ankle complex?

      2. Not every patent is put into use, or when put into use, fail to do as envisioned. So, tell me the model of the recreational, high end boot, with the corresponding patented features you are referring to, that controls only the ABNORMAL biomechanics of excessive STJ pronation. Enough with discarded or unproven theories and patents, that do not present themselves, in the real world.

  5. Knee position is a reflection of obligatory internal leg rotation as a result of normal STJ coupling and a synergistic postural response in the body via the kinetic chain. It may be altered by alignment variants, not by normal foot pronation.

    1. Could you please translate that statement into language that a simple person like me can understand?

      1. Clarifying my nebulous comment!!! Could Kim Hewson please translate that statement into language that a simple person like me can understand?

      2. I will have a go at clarifying what Kim said. In a nutshell, there is no such thing as knee angulation, knee drive etc. The STJ is a mechanical torque converter that translates rotation about the long axis of the foot into vertical axial rotation of the whole leg on approximately a 1:1 ratio. It doesn’t matter whether you are dead or alive. If you grasp the foot of someone who is unconscious or even a cadaver and rotate their foot about its long axis the leg will simultaneously rotate about its vertical axis. From a perspective of functional anatomy, the rotation is obligatory, not optional. At small angles of the knee, the rotation of the whole leg is less perceptible than it is at larger angles where the knee appears to move independently of the leg. This is an illusion. The entire leg is rotating (ergo, the shin and thigh) not just the shin as some appear to believe. The angle of the knee makes it appear to move from side to side in a sweeping arc as the leg rotates. Some ski pros and coaches talk as if the knee were the driver of the edging process and that it is the central joint of the lower limbs instead of an accessory joint.

      3. Hey Mike. Nice to know that you are still thinking and doing. David filled in well for me and I hope you get my point. Coupling means that two movements occur simultaneously. When the foot is on the ground it is relatively fixed (closed chain) in position. In a weight bearing position the foot pronates normally and the talus rotates medially in doing so. That sets up the ankle joint (tibio-talar) in an internally rotated position as well. The two joints( STJ and ankle) must move together so that dorsiflexion of the ankle over the fixed foot means that the overlying leg rotates internally. The movement are simultaneous and harmonious in a 1:1 ratio. That’s why you are so elated with your new-found ankle flexion in loosening your boot buckles that you describe so well. I have called this situation a “captured foot” syndrome. The problem lies at both joints and if you trap one you trap the other because they work together. Make sense?

        Leg internal rotation is initiated at the foot and the leg muscles react in a synergistic fashion. The proprioceptive recognition sensed in the foot-ankle complex leads to a continued internal rotation of the entire leg. This is what I mean by a “postural response”. We have called it a kinetic chain reaction in the past but it’s fun to break it down to understand it better.

        Nice to hear from you again. Please come back to Telluride to visit and ski with old friends.

      4. Further to Kim’s comments I offer the following from David Winter’s paper on balance: “Thus it appears the CNS recognizes the need to stabilize the joint closest to perturbation first, followed by the knee, hip, and spine”. In typical ski maneuvers, perturbations arise mainly from changes in terrain and snow texture. If the normal ankle physiology is disrupted, which is the stated intent of the majority of ski boot work, then balance will be disrupted at its roots.

    2. Oh, That Dr. Kim. I knew the name sounded familiar! Sorry 😦

      The problem most skiers experience is excessive STJ pronation during a turn, An unsupported foot, does not stay in STJ neutral, during a turn.

      It’s desirable to control excessive STJ motion in order to control the amount of tib-fib internal rotation.This keeps the CKM from positioning too far to the inside of the edge, over stretching for the MCL, and to lessen the effects of a mal-tracking patella..

      1. Quote from a well known fitter: “The job of a footbed is to balance your feet through and along the center, to allow equally achievable tipping movements from side to side. It should be comfortable and supportive yet not restrictive of functional movement.”
        Are you suggesting this is wrong and that functional movement should be limited more? Functional movement refers to the ability to tip the feet almost to the full range of movement.

      2. Matt, The quote you used is 100% correct, in what it says, and covers what I said about controlling and guiding the movement of the STJ. Who can you attribute that quote to? If you had read my other posts, you would know that I do NOT want to lock the STJ. I saw the locking of the STJ, with the use of cork and epoxy molded Superfeet, as a huge negative, over 30 years ago. Is it possible I can still change some peoples’ mindset? I also want to change the mindset created by the 70s way of thinking, that an unsupported foot is better for skiing. In my early podiatric medical school training in biomechanics and orthotic creation, we were taught that we DID NOT want to lock the STJ. In those days, no other medical speciality had a clue. Today, too many still do not respect the foot! Plenty of physicians, today, when examining for knee pain, without a history of direct trauma, still refuse to look at the biomechanics of the foot and it’s affect on gait and the knee!

      3. For some reason there was no reply button under your statement below.

        Anyway, great to hear it was just a misunderstanding. I did read your previous posts and I did not think you are trying to lock the STJ, just restrict it more than what the quote I provided suggested. You wrote “An unsupported foot, does not stay in STJ neutral, during a turn.
        It’s desirable to control excessive STJ motion in order to control the amount of tib-fib internal rotation”
        I suppose it is a matter of what “excessive STJ motion” means in terms of RoM.
        The quote was from HH.
        I still think that you probably restrict the movement more than HH and David would though.

      4. Matt, You said,”I still think that you probably restrict the movement more than HH and David would though.”

        Two things. 1. You’re wildly guessing, and you guessed wrong 🙂 2. I have always felt HH built his biomechanics “theories”, ignorant of basic lower extremity biomechanics. His latest book (yes I have his books), still does not get it correct. I do not fault him for not understanding this subject, just that he claims he does!

        So, in your opinion, when is excessive internal rotation of the leg at the knee, too much? When is the opening of the medial aspect of the knee (over stretching the MCL), too much? When is maltracking of the patella, too much? Will you at least admit, all of this has to be evaluated on an individual basis?

        And not to deliberately confuse things, how do you account for base edge angle?

      5. I wasn’t wildly guessing. I actually read your webpage and I have been following HHs writings for years and all posts here made by David. For example HH suggests that the ankle bone should rest against the inside boot shell and you can punch it for comfort and you don’t. This means HH allows more pronation in his insole setup no? Not a big difference but there is one.
        I agree fully that everything has to be evaluated on an individual basis and it must be done partly on snow.
        Regarding the base edge angle. If you are slicing and balancing on the edge it will not make any difference in terms of the knee position, its just a matter of how much the edge is locked into the snow. However, if you are skidding or seeking grip the skier may place the knee too far to the inside in order to find grip. If in this case you cannot tip your foot you may push the knee to the inside to find grip. Not good. IMO one of the most important step in boot fitting is to find a combination of base edge, cuff edge, varus adjustment, insole forming, heel height etc to allow for a natural tipping and balancing of the feet to find the edge grip.
        What I find very interesting in Davids writing is how all this also relates to ski chatter. Both the STH and knee has to be on the inside of the GRF, but not a lot.

      6. Matt, edge chatter, which goes way back to the days of leather boots, is really inversion-eversion (or out and in) edge angle oscillation. For the sake of simplicity’s, I am going to refer to the effect as edge angle oscillation. In future posts I will elaborate on this. It a nutshell, it is a slip-catch mechanism resulting from an inversion moment of force with a moment arm created from a lateral (outside turn aspect) offset between the centre of force applied to the outside ski by the foot and the inside edge. The moment of force is translated through the torque converter in the STJ to whole leg external rotation. Contrary to what some seem to believe, the whole leg rotates as a unit and not the portion of the leg below the knee. A neutral position of the STJ guarantees that the position of the center of force applied by the foot will set up an inversion moment arm. It is not the position of the knee that is the issue. It is the position of the applied force and whether the skier has successfully established a platform of GRF under the outside foot of a turn.

  6. Who in the ski industry, says the STJ, should be locked? Please cite the ski literature that says that, so we can address the root of the problem.
    This is what the first SuperFeet did, and can still do, if the boot tech screws up.

    If, for skiing, the motion at the STJ is guided and controlled, what would that do to your thinking?

      1. Good question.

        First, what is the optimal knee position (and skeletal alignment) over the inside edge, are you trying to achieve during the most stressful part of the turn?

        Second, what would you do to the orthotic to achieve this?

        Third, with other things being equal, if we use STJ neutral as a reproducible reference point, how much do we need the foot, arch and ankle to drop and roll (pronating) and internally rotating, during the most stressful part of the turn, while at the same time, preventing excessive inward positioning and internal rotation of the knee?

        As a frame of reference: When I am casting a runner in STJ neutral, I write the prescription to allow 4 degrees of STJ motion. This creates a functional orthotic, i.e., it allows the arch to function properly as a shock absorber, while preventing excessive pronation. A the same time, the orthotic guides GRF alone the lateral aspect (lateral column) of the foot, until it is time for the forefoot to transfer weight to the hallux for efficient toe-off. In skiing, we want to able able to control the medial column (arch), and 1st ray (navicular, 1st cuneiform and 1st metatarsal).

    1. The original article doesn’t state that the ski industry says the STJ should be locked; but unfortunately that is what the status quo of ski boot design and boot fitting does to skiers. First they cram you into a boot 2 sizes too small, the “race fit”. Then you are supposed to tighten the buckles to immobilize your foot even more. Throw in a footbed with an arch that has absolutely give. Then the skier has to buy a custom fit liner for several hundred more dollars which takes away any remaining mobility. Now that the skiers toes are crushed together, no blood much less feeling can get to the feet, the ankle can’t flex forward much less roll side to side, now they cant the whole mess by grinding the boot sole for another couple hundred dollars which totally destroys any chance of making that boot useful. Quite frankly, a miracle anybody still skis!! After 20 years of trying to figure out a better way, I realize the best skiers can move within their ski boots in spite of the boot’s design and the state of the art useless boot fitting techniques. 20 years ago if I had gone backwards 15 years and realized that all I had to do was what this dude had discovered and allowed my ankles to flex instead of listening to the “experts” and tightened my boots, I would have been having even more fun skiing!!!!!!!!!!!!!!

      1. Michael, I can relate. My experience was similar. The big epiphany I had about 1977 was the realization that the best skiers I was trying (unsuccessfully) to emulate were able to ski in spite of the ski boots not because of them.

      2. Michael, I have been custom fitting boots, for over 30 years. What you describe is what boot fitters used to do. That WAS the status quo. The driving factor for most of that, was the skier’s demand for downsizing, not the boot fitter’s! The skier wanted to lock up their foot, because they felt it moving inside the boot. The direct cause of THAT movement, was…. excessive STJ motion. When the cork moldable Superfeet insole was first introduced, for the most part, it contributed to the locking of the STJ, but it did stop the foot from moving around, It fixed on problem, but created others.(The unintended consequences!) Back then, the Superfeet designers did not understand that it was not good to lock the STJ. To this day, if a boot tech improperly makes a custom insole, the same thing can happen, but it’s not the norm, nor any “status quo” standard.

        It’s a mistake to think of current boot design, as some sort of big mistake. You’re cheating yourself, if you do. Forgetting about everything else, once a boot fitter gets rid of all the pain, caused by foot’s shape,, 90% of what is left, is the skier’s inability to maintain an “over the boot and ski” position. Leaning back, creates discomfort.

        Of course, my main interest is in fitting the 90%. I fit the other 10% far differently.

        BTW, is “dude” some sort of “status quo” standard?:-) You can’t blame the boot designers for bad boot fitters. That blame lies at the feet of the ski shop owner. There are plenty of expert boot fitters I can sit down with, and have a discussion on the “dark arts” of boot fitting. Each would contribute their little discoveries, to the whole of “The Assessment and The Process” !

        And………it’s not 1977, any more. Everyone get over it.:-)

      3. There is a wealth of patents that describe structures of ski boots that intentionally suppress the physiologic mechanisms that dissipate perturbations in GRF and transfer the shocks up the lower limbs to …… 3 guesses? They are all available online. You might want to check them out Robert.

      4. I was at NW lab 2012 as part of the SuperFeet visit.
        Chris Smith was holding firm to the STJ locking and Dr Root biomechanics. And I am a bit confused: in my podologie school in the netherlands we learned Lavigne insoles (shaft pads, arch support, etc etc)
        Since we do custom Superfeet in all our bootfitting (except pathologie) we have a higher succes rate and less returns.

        So are Dr Roots ideas dying or do we simply not know or have a better proved technology?
        (Excuse for my English)

        Greetings from Amsterdam

      5. Hello Marco-Paul. The issue as I see it is how a problem is perceived. I don’t know the history of the origins of STJ neutral locking let alone any theory behind it. But from a holistic skier/equipment systems approach, it makes no sense to me. When I first started modifying ski boots about 1972 (out of necessity) I was trying to learn as much as I could about what I thought was the science of boot-fitting. In 1975 I ended up going to a 3 day boot-fitting course put on by a company from Vermont (I believe it was called The Tool Company). The focus of the course was how to resolve customer complaints. If an inside ankle rubbed against the shell wall you put an arch support in the boot or a heel lift or both. If the forefoot ached because the boot was too narrow, you put in a metatarsal pad and perhaps a custom footbed. Since boot shells tended to be narrow, keeping the arch from ‘collapsing’ (a misnomer if there ever was one) with a footbed that put the STJ in neutral solved the problem by keeping the ankle centred in the shell. After the course I started using all these methods. But they didn’t seem to help people ski better. In some instances, they made people ski worse. Keep in mind that I was working with National Ski Team racers by 1977 and elite skiers in Whistler. So these skiers could sense when something was affecting their skiing.

        So long as everyone is doing the same thing (putting footbeds in every ski boot and skate), it is impossible to see if something is causing a problem. This is why I ended up designing the open architecture research vehicle called the Birdcage with a biomedical engineer. The Birdcage constrained the skier’s foot with discrete minimal contact with the key mechanical points of the foot we had identified. This device allowed us to adjust and fine tune the components that affected skier balance and ski control. With a device like the Birdcage it is possible to capture data that represents a skier’s balance signature; the equivalent of a balance DNA. Since we have distilled the skier/ski interface down to the absolute minimum we can very accurately find out how introducing a footbed, especially a footbed that claims to lock the STJ in neutral, will affect the skier’s performance by capturing data with the footbed in the device then comparing the captured data to the skier’s balance signature data. We could do this over 20 years ago. With the data acquisition technologies available today it is possible to tell what affects a skier including what they ate for a lunch a week ago and whether it gave them indigestion. If I were making claims for a product I would be very careful to ensure that I could defend those claims. If there is merit in STJ neutral I have yet to see evidence of it.

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