ankle joint

WHY STANCE TRAINING IS ESSENTIAL

When readers click on my blog address at skimoves.me, analytics give me a hierarchy of the countries with the most views and the most popular posts in ascending order. This helps me identify which content resonates most strongly with viewers and which content draws a blank.

As I write this post, the top five countries are the US followed by Croatia, the United Kingdom, Slovakia and France.

The most viewed post today is THE SHOCKING TRUTH ABOUT POWER STRAPS; far and away the most popular post I have published to date. But the most important posts by far that I have ever written, A DEVICE TO DETERMINE OPTIMAL PERSONAL RAMP ANGLE and STANCE MUSCLE TENSIONING SEQUENCE EXERCISE barely sputtered in comparison. This strongly suggests that far from just some small gaps in the knowledge base skiing is founded on, massive craters exist.

Arguably the most important aspect of skiing is a strong stance. Any variance in the fore-aft angle of  the plane of support under the feet and the plane of the base of the ski has significant impact on stance. Yet these subjects are barely blips on the Doppler Radar of the ski industry.

Since I started the dynamic ramp angle assessment project a few weeks ago I have found that when asked to do so, it is rare for a skier of any ability to be able to assume a strong ski stance in an off the ski hill environment. Even when a skier  skis with a relatively strong stance, they seem to lack a sense of what a strong stance feels like. Because of this, they lack the ability to consciously replicate a strong stance. If asked to do so, they would be unable to coach a skier in the sequence of events that I described in my last post

In the dynamic ramp angle assessment project, I  have also observed that skiers with with a boot/binding ramp angle greater than 2.8 degrees appear to have become accustomed to the associated unstable, dysfunctional feeling and identify with it as ‘normal’. Before I can test them, I have to spend time coaching them into the correct stance because it feels unnatural to them.

When I go back and forth between a strong functional stance on a flat, hard level surface to a stance on the dynamic ramp angle device set to an angle of 4 degrees, I can get close to the same angles of ankle, knee and hip. But when I do, I feel strong tension, stiffness and even pain in my mid to lower back which is  common in some skiers and even racers.

Based on results to date with the dynamic ramp angle device, it appears as if strong skiers ski best with ramp angles close to zero. But depending on their sense of balance and athletic ability, they may have a wide range in which they sense little difference on the effect of ramp angle until they approach the upper limit of stability. While they may be able to ski well with a ramp angle close to the maximum limit of stability, ramp angles much above 1.2 to 1.5 degrees may not offer any benefits. This can only be tested on skis where balance is tested by dynamic forces which cannot be replicated in a static setting.

Issues affecting skier stance were discussed in detail in my post, THE SHOCKING TRUTH ABOUT POWER STRAPS. Here are the excerpts I posted from the chapter on The Ski Boot in the book, The Shoe in Sport (1989), published in German in 1987 as Der Schuh Im Sport– ISNB 0-8151-7814-X

“If flexion resistance stays the same over the entire range of flexion of the ski boot, the resulting flexion on the tibia will be decreased. With respect to the safety of the knee, however, this is a very poor solution. The increasing stiffness of the flexion joint of the boot decreases the ability of the ankle to compensate for the load and places the entire load on the knee”. – Biomechanical Considerations of the Ski Boot (Alpine) – Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland

“The shaft of the boot should provide the leg with good support, but not with great resistance for about two thirds of the possible arc, i.e., (14 degrees) 20 to 22 degrees. Up to that point, the normal, physiologic function of the ankle should not be impeded”.

“Previous misconceptions concerning its role in absorbing energy must be replaced by the realization that shaft pressure generates impulses affecting the motion patterns of the upper body, which in turn profoundly affect acceleration and balance.

“When the lateral stability of the shaft (the leg) is properly maintained, the forces acting in the sagittal direction should not be merely passive but should be the result of active muscle participation and tonic muscular tension. If muscular function is inhibited in the ankle area, greater loads will be placed on the knee”. – Kinematics of the Foot in the Ski Boot – Professor  Dr. M. Pfeiffer – Institute for the Athletic Science, University of Salzburg, Salzburg, Austria

It has been over 40 years since international authorities on sports science and safety raised red flags concerning the adverse effects of ski boots design and construction on skier stance, balance and the potential to cause or contribute to injury. It is time that their concerns were taken seriously and acted on. Research on stance and the effect of such things as zeppa and delta ramp angles is urgently needed.

 

THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: CLOSED CHAIN OUTSIDE LEG ROTATION

A recently published study on foot pressure data acquired during skiing (1.) recognized that compressive force pressure data acquired in skiing is underestimated by 21% to 54% compared to pressure data acquired on a force platform in a controlled environment.  The underestimation varies depending on the phase of the turn, the skier’s skill level, the pitch of the slope and the skiing mode. The paper states that other studies have stated that this underestimation originates from a significant part of the force actually being transferred through the ski boot’s cuff (to the ski). As a result, the CoP trajectory also tends to be underestimated along both the anterior-posterior (A-P) and medial-lateral (M-L) axes compared to force platforms.

In conclusion, these studies have highlighted a major contribution of different factors to the nGRF applied throughout a turn, such as the foot’s position during a turn (inside vs. outside), the CoP A-P (front to back) displacement, or precise loading of different foot sole regions.  Unfortunately, these results have been studied separately.

There is a lack of continuity across the various positions in skiing and, in particular, a lack of a model with which to explain mechanisms such as balance on the outside ski and open and closed chain internal rotation of the leg and foot in conjunction with progressive inclination and G force loading on it as the skier crosses the fall line in the bottom of a turn. The associated mechanics and biomechanics represent a new paradigm requiring new thinking and new insights. Existing text-book explanations are not sufficient to explain these mechanisms.

Open Chain Whole Leg Rotation vs. Closed Chain Rotation

Rotation of an unloaded (non-weight bearing) lower limb is relatively straight forward when there is a small angle at the knee. As resistance to rotation of the foot is progressively introduced with increasing weight imposed on it, the kinetic chain begins to close. As it closes, the points at which the foot transfers torque to the walls of rigid shell footwear such as ice skates and ski boots starts to emerge as an issue as does the loading of the foot created by the weight of the body imposed on it and the position of COM in relation to the foot.

In order to tension the biokinetic chain and trigger the two-phase Second Rocker, COM must be aligned over the foot as shown in the grahic below.  This alignment requires that the leg adduct (move towards the center of the body) approximately 6.5 degrees. To bring the 3 points of the tripod of the foot into contact with the ground, the foot must evert (sole turn outward) the same amount. Eversion is accompanied by a corresponding torque coupled 6.5 degrees of internal rotation of the leg as shown in the left hand figure in the graphic below (see my post – OUTSIDE SKI BALANCE BASICS: STEP-BY-STEP). The bipedal figure on the right shows adduction, eversion and internal rotation as 0.0 – 0.0 – 0.0 for reference. The monopedal figure on the left shows the changes in adduction, eversion and internal rotation as 6.5 – 6.5 – 6.5.

 

The alignment of COM with the foot can be achieved by moving COM laterally as shown by the arrow emanating from COM in the Monopedal figure or by moving the foot medially as shown by the white arrow or through a combination of the two movements.  The act of positioning COM over the outside foot (Getting Over It), sets in motion internal rotation of the outside leg and eversion of foot into the turn. This engages an over-centre mechanism between the platform of the ski and the inside edge underfoot.

The over-centre mechanism results in an alignment of the resultant force R forming an angle with the transverse aspect of base of the ski that is slightly less than 90 degrees. In order to Get (COM) Over It (the foot), it is essential that the outside leg is not only able to adduct and rotate internally as the foot everts, but to achieve this configuration without delay in order to set up the over-center mechanism. The problem for the majority of skiers is that the objective of most boot fit systems and boot-fitting procedures is to support the foot in a neutral configuration. Eversion of the foot is a component of pronation. Impeding or preventing pronation, restricts or even prevents the required amount of eversion.

Closing the Kinetic Chain on Whole Leg Rotation

Open kinetic chain leg/foot rotation with the foot unloaded (not bearing weight) is relatively simple. But the mechanics and biomechanics begin to get complicated when resistance is progressively introduced that starts to close the kinetic chain as happens when the outside ski is rotated across the path of the skier in the fall line in the bottom of a turn.
The graphic below shows a foot supported on a platform with 2 points of resistance (FR) applied to the platform opposite the 2 points of application of the moments of force, ML (green) and MM (red). The forces tangent to the arc of the moments of rotation are shown as FT.
When the weight of the body is progressively shifted to one foot (i.e. Monopedal Stance) and the foot everts, the talus (shown in gray in the graphic above) moves inward towards the center of the body and shifts slightly rearward as evidenced by the corresponding movement of the inside ankle bone.  This is easily seen when moving from bipedal to monopedal stance on a hard, flat surface while barefoot. In order to effectively transfer torque from the foot to the platform, the forefoot and ankle and knee joints must be fascially tensioned. This requires that the big toe (Hallux) be aligned on the anatomical axis (dashed line) and the forefoot fully splayed. This stabilizes the heel and head of the 1st metatarsal (ball of the foot).  Torque from internal rotation of the leg will be transferred to two discrete points adjacent the Load Counters mounted on the resistance platform.

Removing the resistance force FR from the inner (big toe) aspect of the platform provides insights to what I refer to as the Turntable Effect that is associated with internal rotation of the leg and eversion of the foot that creates an over-center mechanism. The turntable rotation is shown in light yellow. The effect will vary for different structures of the foot depending on the location of the center of rotation of the platform under the foot.

The location of the blade of an ice skate on the anatomical center of the foot has been used to explain why it is easier to cut into a hard ice surface with a skate compared to the edges of a ski. But the real reason it is easier is because ice skaters use the Second Rocker, Over-Center, Turn Table Mechanisms as shown in the graphic below. The skate is positioned under COM. It can be readily seen that the skater is not using the inner aspect of the shaft of the skate to hold the skate on edge.

In my next post, I will discuss the progress of emerging CARV and NABOSO technologies after which I will continue with my discussion of the Mechanics of Balance on the Outside Ski.


  1. Influence of slope steepness, foot position and turn phase on plantar pressure distribution during giant slalom alpine ski racing: Published: May 4, 2017  – Thomas Falda-Buscaiot, Frédérique Hintzy, Patrice Rougier, Patrick Lacouture, Nicolas Coulmy
  2. http://wp.me/p3vZhu-29n

BOOT-FITTING 101: THE ESSENTIALS – SHELL FIT

In this post, I am going to discuss the process I follow to assess what I call the essential foot to shell clearances. This is a 2-step process.

Step 1 – Establish the clearances between the structures of the foot and the inner wall of the boot shell required for the foot to function.

Step 2 – Establish the physical connections between discrete restraint force transfer areas of the foot and the inner walls of the boot shell required for the effective force transfer to the ski, for containment of the foot required to support the processes of balance and for the coupling of the foot to specific mechanical references in the boot shell related to the running surface of the ski.

As a prelude to discussing shell fit, it is necessary to point out that a major shift is occuring in the area of focus on the human foot.

Until recently, most discussions on the human foot have focussed almost exclusively on the rearfoot; the ankle complex, the tibial-talar and sub-talar joints, ankle dorsiflexion and plantarflexion, ankle mobility, inversion, eversion, etc. This limited focus has been at the expense of an appreciation and understanding of the role of the forefoot and the complex lever mechanism that enables the first MTP joint to apply large forces to the ground. A study (1) published in 2004 commented:

The plantar aponeurosis (plantar fascia) is known to be a major contributor to arch support, but its role in transferring Achilles tendon loads to the forefoot remains poorly understood.

 Fascia is a sheet or band of fibrous tissue such as lies deep to the skin or invests muscles or various body organs.

The most plausible reason why the role of the  plantar aponeurosis in transferring Achilles tendon loads to the forefoot is poorly understood is that it has not been given much attention until recently.  

The above cited study concluded:

Plantar aponeurosis forces gradually increased during stance and peaked in late stance.

The almost exclusive focus of attention on the rearfoot has led to assumptions about the function of the foot as a system which are only now being called into question and found to be erroneous or invalid. One result is the erroneous assumption that the arch of the human foot is weak and collapses under the weight of the body. This has spawned a lucrative market for custom made arch supports intended to provide what is perceived as needed support for the arch of the foot.

In boot-fitting, the process of fascial tensioning, in which the height of the arch decreases and the forefoot splays, has been misinterpreted as an indication of a collapsing (implied failure) of the arch due to its inability to support the weight of the superincumbent body during skiing maneuvers. This has led to an almost universal perception and acceptance in skiing of custom arch supports as essential foundations for the foot and the most important part of a ski boot.

The Fascial Tension/SR Stance Connection

Plantar aponeurosis forces peak in late stance in the process of fascial tensioning where they act to maximally stiffen the foot in preparation for the application of propulsive force to the ground. When fascial tensioning of the plantar aponeurosis peaks, forward rotation of the shank is arrested by isometric contraction of the Achilles tendon. This is the shank angle associated with the SR Stance.

Immobilize – Support – Stabilize

Discussions of foot function in the context of the foot to shell clearances necessary for foot function and especially fascial tensioning, tend to be obscured by a consistent, persistent narrative in the ski industry spanning decades that the foot should be supported, stabilized and immobilized in a ski boot. Foot splay, associated with fascial arch tensioning, is viewed as a bad thing. Efforts are made to prevent foot splay with arch supports and custom formed liners in order to the fit the foot in the smallest possible boot size in the name of optimizing support.

In the new paradigm that exists today, the foot is increasingly viewed in the context of a deeply-rooted structure. In the design and fabrication of footwear, attention is now being directed to the accommodation of the  fascial architecture  and the importance of fascial tensioning as it pertains to the science of the human lever mechanism of the foot.

Fascial Tensioning and the Human Foot Lever

Fascial tensioning is critical to the stiffening of the foot for effective force transmission and to foot to core sequencing.

The body perceives impact forces that tend to disturb equilibrium as vibrations. It damps vibration by creating fascial tension in the arches of the foot and the lower limb. Supporting the structures of the foot, especially the arch, diminishes both the degree and speed of fascial tensioning to the detriment of the processes of balance and the ability to protect the tissues of the lower limbs through the process of damping of impact forces.

Dr. Emily Splichal has an excellent webinar on The Science of the Human Lever – Internal Fascial Architecture of the Foot as it pertains to foot to core sequencing – https://youtu.be/_35cQCoXp9U

The DIN Standard is Not a Foot Standard

A major problem for the human foot in a ski boot is the DIN standard toe shape. DIN stands for ‘Deutsches Institut für Normung’ which means ‘German Institute of Standardization’.

The DIN toe shape creates a standard interface for bindings. In a strong, healthy foot, the big toe or hallux should be aligned straight ahead on the center axis of the boot/ski. But as an interface for the human foot, the DIN standard toe shape of a ski boot is the equivalent of a round hole for a wedge-shaped peg.

The graphic below shows a photograph of a foot overlaid over a photograph of the ski boot for the same foot. The outline of the wall of the boot is shown in red. Even though the length of the boot shell is greater than the length of the foot, the big toe will be bent inward by the wall of the shell using the one finger space behind the heel shell length check.

screen-shot-2017-02-09-at-3-55-38-pm

The Importance of Foot Splay

The progressive fascial tensioning that occurs as CoM advances over the foot transforms foot into a rigid lever that enables the plantar foot to apply force the ground or to a structure underneath the plantar foot such as a ski or skate blade. Forefoot splay is important to the stiffening of the forefoot required for effective plantar to ground force transfer.

Ski boot performance is typically equated with shell last width. Performance boots are classified as narrow. Such boots typically have lasts ranging from 96 mm to 99 mm. Narrow boots are claimed to provide superior sensitivity and quick response, implying superior control of the ski.

The outside bone-to-bone width shown in the photo below is not quite 109 mm. The boot shell has been expanded. The 2 red arrows show the 5th and 1st toe joints (metatarsophalangeal joint or MTP joint). A prime hot spot in less than adequate shell width in the forefoot, is the 5th MTP joint. Even a minimal liner will narrow the boot shell width by 3 to 4 mm.

mt-width

Shell Check: Start Point 

I start with a skier standing in both boot shells with the insole in place from the liner then have them claw each foot forward in the shells using their toes until they can just feel the wall of the shell with the outside (medial) aspect of the big toe when they wiggle the toe up and down. If there is a finger space behind the heel, the shell is in the ball park.

A second check is made with the skier standing on one foot. Some allowance for the correct alignment of the big toe  can be made by grinding the inside of the shell where it is forcing the big toe inward. When fully weighted, a fascially tensioned forefoot will splay approximately 3 mm for a female and 5 mm for a male.  The ball shaped protrusion of the 5th MTP joint is typically almost directly below the toe buckle of a 4 – buckle boot.

Once a skier can stand on one foot in each shell with adequate space for normal foot splay, the rear foot can be checked for clearance. The usual sources of problems are the inside ankle bone (medial malleolus) and the navicular and/or the medial tarsal bone. A good way to locate the prime areas of contact is to apply a thick face cream or even toothpaste to the inside ankle bones then carefully insert the foot into the boot shell, stand on it to make contact with the shell, then carefully remove the foot. The cream will leave tell tale smears on the boot shell which can then be marked with a felt pen.

Getting Step 1 successfully completed can involve alternating back and forth between forefoot and rearfoot clearance. Until, both areas are right, full normal foot splay may not occur. Step 2 is done in conjunction with liner modifications which can be a process in itself and is often the most problematic aspect of creating an environment in a ski boot that accommodates and supports foot function especially fascial tensioning.


  1. Dynamic loading of the plantar aponeurosis in walking – Erdemir A1, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA  – J Bone Joint Surg Am. 2004 Mar;86-A(3):546-52.

SKIER LEG SHANK ANGLE VS. BOOT SHAFT ANGLE

The lack of proper technique seem so often is not due to a lack of ability, but to an unsatisfactory functional configuration of the shaft in so many ski boots.

–  Sports Medical Criteria of the Alpine Ski Boot – W Hauser P. Schaff, Technical Surveillance Association, Munich, West Germany – The Shoe in Sport (1989) – published in German in 1987 as Der Schuh Im Sport – ISNB 0-8151-7814-X

In a conventional ski boot, the rear aspect and sides of the shaft are fixed in relation to the shell lower with the result that the angle of the rear spine of the shaft is fixed. The leading edges on either side of the shaft, overlap at the forward aspect where they are drawn together by closure means. In this configuration, the angle of the shank of a user is dependent on the degree with which the closures draw the uppermost forward aspect of the leading edges of the shaft towards each other, and towards the rear spine, in proportion to the amount of overlap created by the operation of the closure mechanism.

The graphic below shows two photos of a right ski boot shell. In the left photo, the shaft buckles are operated to the minimal closure position. In the right photo, the shaft buckles are operated to the maximal closure position. A red reference line at the rear spine indicates the fixed shaft angle. A red reference line at the front aspect of the shaft overlap indicates the variable aspect of the shaft angle is it pertains to the shank angle of the user. An arbitrary reference center with which to gauge the variance in the shank angle is shown in black. The reference shank angle in the maximal closure position (right boot) is 8 degrees less than the reference shank angle in the minimal closure position (left boot). In terms of angles of ankle flexion, the ankle of the same foot and leg in the boot shell in the right photo would be 8 degrees plantarflexed when compared to the ankle of the same foot and leg in boot shell in the left photo.

Shank difference

The implications of this arrangement are that the shank angle of the user will change in response to changes in the operation of the closures of the shaft, especially changes in the top shaft closure and/or the amount of tension in the power strap, if equipped with one. For the most part, racers are unaware of the critical nature of the correct shank angle. They have erroneously assumed, or have been taught, that a securely tightened shaft is essential for good control of the ski. The tighter the shaft is secured to the leg, the better the control. As shown in the photo below, boot makers provide shaft buckles with high leverage features that facilitate a secure closure of the shaft with the leg. Closing the boot shaft beyond the shank reference angle can have serious implications for balance and control of the ski.

Leverage boost

The angle of the shank of the user is dependent on the degree of overlap of the leading edges of the shaft, including the tension of any power strap. The cross-sectional area of the leg of the user at the boot top, in particular, the front to back dimension of the cross-sectional area, is also a factor that affects the correct angle of the shank.

The two photos below compare the shaft angle of a stock boot shell to the shaft angle of a boot shell that has been modified to reduce the shaft angle by 8 degrees in order to correct for excessive shank angle.

8 degree difference

Operating the closure mechanism of a shaft beyond a certain point creates another problem, as shown in the photo below, deformation of the interfaces of the overlap elements of the shaft.

Overlap deformation

The angle of the shank of a racer is critical. It must be maintained within a narrow range for optimal performance. Anything that has the potential to alter an optimal shank ankle should be carefully evaluated.

Related post: GETTING SHAFTED BY THE (SKI BOOT) SHAFT -https://skimoves.me/2014/04/09/getting-shafte…ski-boot-shaft/

 

 

TONGUE TIED

This post is about how tongues in ski boot can affect balance.

Every ski boot has some sort of tongue. In the case of rear entry boots or liners like the Intuition, a portion of the liner acts in the capacity of a tongue. So what exactly does the tongue do? The obvious job of the tongue is to the pad the shin and spread the load applied by the shank to the front of the boot shaft.

What about the forefoot portion of the tongue over the instep of the foot? What does it do? As far as I have been able to ascertain, for most skiers, not much. Seriogram X-Ray studies done for me in 1995 found that in the boots of some skiers, there was a significant crash space between the top of the forefoot portion of the tongue and the inner surface of the boot shell. A lack of constraint or load applied to the instep of the foot of a skier means that the entire foot can float within the boot shell in response to perturbations in snow reaction force. Typically, when a skier’s CoM is perturbed, the plantar foot separates from the insole on the liner. If the skier is thrown off balance and pitches forward, the heel of the foot moves up as the foot rotates about the balls of the foot. This is an issue that the in-boot technology in my US Patent No. 4,534,122 addressed.

But ski boot tongues can do other things that you may not be aware of. The tongue can act in the capacity of a spring that opposes and progressively loads the shank in ankle flexion. Worse, it can  obstruct the glide path of the ankle joint. When the now ubiquitous power strap that is present on most boots today is cinched up tight, the tongue can act as an effective splint for the ankle.

In my last post, MOMENT OF THE SHANK IN THE SHAFT,  I used a simulation to show how my shank can move with little resistance from the shaft for about 14-16 degrees within the front to back free space within the shaft. In his article, Kinematics of the foot in the ski boot, Dr. M. Pfeiffer refers to this as the lead segment of shank flexion. Here is what it looks like in my Head World Cup ski boot.

Lead segment

The red line emanating from the fixation of the shaft of the boot indicates the proximate point about which deformation of the front of the cuff will occur. As my shank encounters the front of the shaft I want the load centre to remain substantially fixed and the resistance to predictably increase so my balance system can work with it.

The load applied by my shank is to the top edge of the front of the shaft of the boot. This is the centre of the load. The load is distributed by the tongue above and below the load centre. I like to have a little more load on my shank below the load center than above the load centre. The red arrows and bar with the dots in the photos below show this. I don’t want to have any load on my shank below the lower aspect of the load distribution.

C of Force

Here is what the stock tongue from my boots looked like after I performed a tonguectomy procedure that removed it from the liner.

Tongue section

Here is what the tongue looks like overlaid on my ski boot.

Tongue overlaid

Note the flat profile. In order for the tongue to conform to my foot and leg either my ankle has to severely plantarflex or my the tongue has to bend. I suspect that tongue is made this way to act as a sort of shank-shaft  shoehorn to facilitate entry of the foot into the boot. Since I can’t stand up let alone ski with my ankle plantarflexed, the tongue has to bend. By what? By my shank applying a force to it. In this configuration the tongue is acting like a spring pushing against the shank of my leg in places where I don’t want any load.

 

I push on the tongue, the tongue pushes back. But it can be worse than that especially if the tongue is too far back as it was in my boots. The tongue is fixed (usually sewn) to the toe box of the liner. The first time I put my boots on (the liners were intact then) and operated the buckles it felt like a steel rod was jammed into the base of my shank. If I tried to flex my ankle I could feel that the glide path of the joint was impeded. So I would get an initial load on my shank at its base followed by a secondary load at the top of the shaft superimposed over the first load. To me, the feeling is like running up a flight of stairs and catching the toe of my lead foot on a stair nosing. I call this kind of unpredictable loading the ‘trip effect’ because it feels similar to tripping in terms of the effect on my balance.

In my next post I will discuss the tongue modifications I typically make.

 

PROBLEMATIC FEET AND LEGS

In my post, THE IDEAL SKIER’S FOOT AND LEG, I described the characteristics that I observed over the years that were consistently associated with the feet and legs of the best skiers and racers. When I first started to see this pattern I didn’t understand why these characteristics were associated with superior technical ability. What I did come to understand very quickly was that skiers with feet and leg shapes that were less than ideal had difficulty skiing without major modifications to their ski boots. The images below compare the ideal foot and leg shape to foot and leg shapes that are increasingly problematic. The dashed line indicates the top of the sides of the cuff of the ski boot shell. The vertical hash marks compare the width of the cross-sectional area of the ideal leg at the top of the sides of the cuff to foot and leg shapes that progressively less than ideal.

Foot and leg types

 

As the cross-sectional area of the legs becomes increasingly larger, it becomes increasingly difficult to accommodate the leg within the confines of a boot cuff. In some cases, leg shapes make it difficult to even close the cuff buckles without extending the bales or re-locating the buckles. These types of fleshy legs are mostly associated with females although some males have the extreme shape depicted in the righthand image.  Females with wide hips tend to have tibias that are either straight or angle inward as shown in the sketch below. This can be a big problem if the cant angle of a boot cuff cannot be adjusted sufficiently to obtain a neutral cuff alignment with legs. Boots with no cuff adjustment, like the old Lange XLR, had cuffs that were canted outward 3 degrees. This meant that female racers with tibias that were straight or angled inward would be hard on their inside edges in events like downhill if they tried to relax and let their skis glide.

Female with wide hipsSome females have tibias that angle inward and fleshy legs. Since the rear spoiler of the boot cuff determines the angle of (dorsi) flexion of the ankle joint, skiers with large calves and tibias that are straight or angle inward have too much forward lean and the wrong cuff cant. When I worked with female racers in the late ’70s and early ’80s it typically took a lot of ingenuity and a lot of work to come up with a solution.

The problem with ski boots is that the shape of the lower part of the shell and the shape of the cuff are usually designed to interface with each other in a specific configuration. This limits the ability to align the cuff in a different position with the lower shell. It was Alan Trimble, the boot tech for Lange USA, who taught me how to make cuts in the shell bottom where it interfaced with cuff, position the cuff in the desired orientation then rivet the two pieces together. Lange was one of the few boots that allowed for this kind of modification.

When I worked with Langes I had a supply of boot parts with no holes drilled in the cuffs. This made it easier to assemble boots in non-stock configurations. The soft Lange fabric liners with fit pockets made it easy to remove padding that was interfering with ankle-leg movements. A common complaint was pressure on the inside ankle bone and even along the inner aspect of the foot below and in front of the ankle. I got very good at stretching the shell wall in this area. I even had special tools made for this purpose. From feedback from racers, I came to know that it was important to not have any pressure on the inner aspect of the ankle and the area around it. But it took me years to understand why. Here is a short video clip that shows the movement of the ankle and leg that is fundamental to the technique racers such as Ligety and Shiffrin use. In a future post I will explain why and how this works.

 

 

PRONATION – WHAT SHOULD IT FEEL LIKE?

Given the widespread confusion and misunderstanding surrounding pronation and it’s role in skiing that seems to exist I am going to provide some drills that will teach you how to assume a functionally pronated position.

Functional pronation is specific to monopedal (one-foot) stance especially as it relates to the ability to assume and move from one dynamically tensioned base of support to another. Once you have a feel for the functionally pronated monopedal position you can go through series of drills standing in your bare feet on a hard flat surface. Next you can stand in your ski boots starting in the boot shell after which you can add the liner with no insole followed by the liner with an insole or custom footbed. By using the feeling associated with standing in your bare feet on a hard, level, flat surface and then comparing the sensations to standing in your ski boots on a hard, level, flat surface you can experience for yourself how the various elements around and beneath the sole of your foot affect your ability to assume a functionally pronated position or even stand properly on two feet. As a prelude to providing drills on how to assume a functionally pronated monopedal stance, I will provide a brief history of the events that contributed to my current position on pronation, footbeds and insoles in general in skiing.

In my initial years of modifying ski boots I was a big proponent of footbeds. In those days, my work on ski boots was very much aligned with conventional views of immobilizing and supporting the foot and leg. But my disastrous experiences with Dave Murray got me rethinking this. By the time I began working with Steve Podborski, I was moving in a direction away from conventional thinking. In 1980, I had a huge breakthrough with a in-boot technology for which I was later awarded a patent. This was the turning point at which  severed any association I had with conventional thinking in ski boots and started fresh with a clean sheet of paper; one that did not include any premises on which existing ski boots are based.

By 1991, when Steve Podborski and I  initiated a research program to test my hypothesis on the mechanics, biomechanics and physics of skiing, my thinking was so far from convention that I insisted on retaining two scientists to provide oversight on the project. This included reviewing everything I put in writing but especially my patent. This process was intended to ensure that the principles I was using were both sound and correct. One of the scientist was G. Robert Colborne, Ph.D, an expert in the biomechanics of the human lower limbs. After reviewing my hypothesis, the initial impression of these scientists was that if it were correct it meant the whole world was wrong. Because I was in uncharted territory it was critical to me to have my findings confirmed before going forward. Once the wheels of a new technology are set in motion and significant money has been invested, it is hard to change direction, and especially to reverse direction. For this reason, we did a series of on snow studies in 1991 on Whistler’s glacier to confirm my hypothesis. I will provide details of the results in future posts.

The image below shows the model engaged in quiet standing Bipedal stance. The major muscles responsible for maintaining COP within the limits of the base of support in the feet in an upright posture or stance are being tensioned in eccentric contraction. There four positions of Centre of Mass in relation to the feet with weight distribution as follows from 1 to 4:

1. Centre of Mass is just in front of the base of the shin. The heel of each foot is carrying about 60-70% of the load. This represents the rearmost limit of Centre of Mass. Should CoM fall behind the base of the shin, a rearward fall will result.

2. Centre of Mass is in the proximate centre of the span of the longitudinal arch. The heel of each foot is carrying approximately 50% of the load. The balls of the feet are carrying the remaining 50% of the load. The ball of the great toe of each foot is carrying twice as much load as the other 4 balls the foot. This position represents the most stable and efficient form of bipedal stance.

3. Centre of Mass is approaching the balls of the feet. The eccentric contraction of the muscles that plantarflex (push down) the feet is increasing. The balls of the feet are carrying the remaining 60-70% of the load of each foot.

4. Centre of Mass is almost over the balls of the feet. The contraction of the muscles that plantarflex the feet has further increased. The muscles that push the toes down are now contracting forcefully, pushing the toes against the floor. This is the absolute forward limit of Centre of Mass in quiet standing. The toes act as a fail safe by pressing down onto the support surface in what is called the Reverse Windlass Mechanism. This mechanism tensions the forefoot into a rigid lever in preparation for propulsive phase of gait. At this point, almost all the weight is being carried on the balls of the feet and the toes. Should CoM pass the balls of the feet without evoking plantarflexion of the ankle, a forward fall will occur.

Screen Shot 2014-02-10 at 10.03.33 AMBIPEDAL DRILLS

These should be done in bare feet on a hard, flat, level surface. Start with the second position.

Drill 1. Stand erect with your feet a natural hip width apart and with a small angle of flexion at the knee joint. Release any tension from your body and allow your feet to settle onto the surface of the floor. Do not consciously apply force with your feet. Tune in to the pressures in your feet and buttocks. Sway back and forth slightly using only ankle flexion. Find the point at which the weight feels even between your heels and balls of your feet. You should feel slightly more pressure under the ball of your big toe than under the balls of your other toes. This is normal. Look down at your knees. They should be aligned straight ahead.

Drill 2. Using only the ankle joint, press down on the balls of your feet until you feel most of the weight on under your heels. Do not go too far. This is the limit of the rearward movement of C0P. At this point you are on the verge of a backward fall. Look down at your knees. They should be aligned straight ahead.

Drill 3. Using only the ankle joint, release the pressure under the balls of your feet until you feel more of the weight on the balls of feet than your heel. Look down at your knees. They should be aligned straight ahead.

Drill 4. Using only the ankle joint, release more pressure under the balls of your feet until you feel the weight pressing down hard on the balls of your feet and your toes. Do not go too far. This is the limit of the forward movement of C0P. At this point you are on the verge of a forward fall. Look down at your knees. They should be aligned straight ahead.

FUNCTIONAL PRONATION MONOPEDAL DRILL

1. Start from position 2 above.

2. Move your Centre of Mass slowly towards whichever one of your feet you most comfortable and confident with.

3. As you move towards one foot allow your ankle and leg to relax and roll inward, towards the L-R centre of your body.

4. When you feel the pressure strongly under the ball of your foot move, allow the ankle to relax and your Centre of Mass to move forward into position 3 above. As this happens lift the other foot off the floor. You will feel a pronounced change in the tension of the gluteus muscles in same side as your support foot in your buttocks. If your foot is functionally pronated you will feel most of the pressure under the ball of your foot.

Congratulations. You have achieved functional pronation and a dynamically tensioned base of support. Now try putting insoles and arch supports under your foot and feet. Do the same drills and see what happens.