Ski Equipment posts


At the time I filed an application for my second patent in April of 1989 , I had some ideas of what a ski boot should do for the user from what I had learned from the dorsal containment system I was granted a patent for in 1983. But I was still a long way from being able to answer the question.

A watershed moment came for me in 1990 when I read a medical textbook published in 1989 called The Shoe in Sport on what is referred to in the text as ‘the shoe problem’.

The Shoe in Sport, supported by the Orthopedic/Traumatologic Society for Sports Medicine, was originally published in German in 1987 as Der Schuh im Sport. The textbook is a compilation of the collective efforts of 44 international experts, including Professor Peter Cavanagh, Director of the Center for Locomotion Studies at Penn State University, biomechanics experts from the Biomechanical Laboratories at ETH Zurich and the University of Calgary, Professor Dr. M. Pfeiffer of the Institute for Athletic Sciences at the University of Salzburg, Dr. A. Vogel of the Ski Research Syndicate, Dr. W. Hauser and P. Schaff of the Technical Surveillance Association Munich and many other experts in orthopedic and sportsmedicine on  ‘the shoe problem’.

The buyers of athletic shoes are always looking for the “ideal shoe”. They encounter a bewildering variety of options and are largely dependent for information on the more or less aggressive sales pitches that directed at all athletes in all possible ways. (1.)

This volume should assist in defining the role and the contributions of science in the further development of the athletic shoe and in the recognizing of the contributions made by the various research groups, who are all interested in the problems of the athletic shoe. (1.)

Dazzled by the fancy names, the buyers believe that they can match the athletic performance of the champion who wears “that shoe,” or after whom the shoe is named. The choice is not made easier by the plethora of promises and a roster of specific advantages, most of which the merchant cannot even explain. (2.)

When The Shoe in Sport was first published in 1987, the field of biomechanics was in its infancy as was the associated terminology. This created an opportunity for a new marketing narrative of techno buzzwords. Since the consumer had no way to understand, let alone assess, the validity of any claims,  the only limits to claims made for performance was the imagination of the marketers. Consumers were increasingly bombarded with features that far from recognising the human foot as a masterpiece of engineering and a work of art as espoused by Leonardo da Vinci, suggested the human foot is seriously flawed and in need of support even for mundane day-to-day activities. These marketing messages distract attention away from the real problem, the design and construction of shoes and their negative effect on the function of the user; the modern ski boot being one of the worst examples.

The Shoe Problem

For this reason, the “shoe problem”as it exists in the various fields of athletic endeavour, will be studied with respect to the biomechanical, medical , and technical aspects of shoemaking. The findings (criteria) should enable the interested reader to distinguish between hucksterism and humbug on the one side and the scientifically sound improvements in the athletic shoe on the other. (1.)

Form follows Human Function

The Shoe in Sport focusses on the medical orthopedic criteria in offering guidelines for the design of shoes for specific athletic activities including skiing and ice skating.

Less attention will be paid to the technical and material aspects of the running surface and shoe, and more to the medical and orthopedic criteria for the (design of) athletic shoe. For this reason, the “shoe problem”as it exists in the various fields of athletic endeavour, will be studied with respect to the biomechanical, medical , and technical aspects of shoemaking. 

This volume should assist in defining the role and the contributions of science in the further development of the athletic shoe and in the recognizing of the contributions made by the various research groups, who are all interested in the problems of the athletic shoe.

Barefoot as the Reference Standard

Research done at the Human Performance Laboratory at the University of Calgary found that optimal human performance is produced with the unshod foot and that human performance is compromised by the degree of interference; the greater the interference caused by any structure appended to the foot, the greater the compromise of performance. This is true even for a thin sock.

The authors of The Shoe in Sport ask:

Is there really a need for shoes? The examples of athletes like Zola Budd and Abebe Bikila suggest in a technologic environment the evolution of the athletic shoe parallels the decline of our organs of locomotion. (1.)

The Future of the Ski Boot

The shoe affects the athlete’s performance and serves to support the foot as a tool, as a shock absorber, and as a launching pad. Giving serious consideration to our organs of locomotion opens up an enormous area of activity to the athletic shoe industry. (1.)

This is especially true of the ski boot. The questions that needs to be asked is how does the structure of the ski boot affect the human performance of skier and what is the minimal combination of structure that will enable maximum skier performance.

Few forms of athletics place as high demands on the footwear used in their performance as alpine skiing. It (the ski boot) functions as a connecting link between the binding and the body and performs a series of difficult complex tasks. (3.)

Before the question of what structure of a ski boot will maximize skier performance can be answered, the functional mode of the human system in the complex physical environment associated with skiing must be known. The first and most important and fundamantal component of this question is explaining the mechanism by which the human system is able to achieve a state of balance on the outside ski characterized by neuromuscular control of torques in all 3 planes across the joints of the lower limb and pelvis.

  1. Introduction by Dr. med. B. Segesser, Prof. Dr. med. W. Pforringer
  2. 2. Specific Running Injuries and Complaints Related to Excessive Loads – Medical Criteria of the Running Shoe by Dr. med. N. L. Becker – Orthopedic Surgeon
  3. Ski-Specific Injuries and Overload Problems – Orthopedic Design of the Ski Boot –  Dr. med. H.W. Bar, Orthopedics-Sportsmedicine, member of GOTS, Murnau, West Germany


The problem associated with measuring boot board (zeppa) and/or binding (delta) ramp angle as individual components is that the resulting angle may not accurately reflect the actual angle between the plane of the base of the upper surface of the boot board and the base of the ski in the boot/binding/ski system. Boot boards of the same zeppa angle may not necessarily have the same zeppa angle with the base of the boot shell due to design and/or manufacturing variances.

A level inserted into a ski boot shell with the boot board in place can be difficult to read. With the liner in place, this is not a viable option. A better option is to extend the angle of the boot board up above the top of the shaft of the boot so it can be accurately and easily read.

A simple device for this purpose can be made for about $25 with basic hand tools and a few screws using 2 – 8 in (20 cm) x 12 in (30 cm) x 1/8 in (3 mm) thick steel carpenter’s squares.

Place the long arms of the squares over each other as shown in the photo below and clamp them securely together. Two-sided tape can be used to help secure the alignment. Then drill a hole  at one point on the vertical leg and screw the 2 squares together.

Check the parallelness of the 2 opposite arms on a level surface with a digital level. If good, secure the 2 levels together with a second screw. Then affix a section of 3/4 in (2 cm) x 3/4 in (2 cm) square or L-bar bar on the top of the extender to rest the level on.

To use the extender, place a boot shell on a hard, flat, level surface. If the surface is not level it should be leveled before the extender is used.

The photo below shows the extender being used to measure the zeppa angle of an old Salomon SX-90 shell. I didn’t have the electronic level for the photo. So I used a small torpedo level.

Insert the lower arm of the device into the shell as shown in the right hand image and place the lower arm firmly on the boot board. Place the level on the top arm and read the angle.

The photo below shows the same process as above. But in this example, the liner is in place. If an insole is in the liner, it should be flat with no arch form. I highlighted the square bar with pink to make it easily visible.

A check of the zeppa-delta angle of the boot-binding-ski system can be done by mounting the boot in the binding of the ski that is part of the system and clamping the ski to a flat surface with sufficient force to ensure the camber is removed and the running surface of the base is in full contact with the supporting surface. A strap wrapped over the front of the boot shell and under and around the supporting surface then tensioned will help ensure that the toe plate of the binding is loaded.

The Zeppa-Delta Angle Extender provides the user with a fast accurate way to know their total number. What’s yours?



When readers click on my blog address at, 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.



In this post, I will expand on the content of The Shocking Truth About Power Straps (1.) which was by far the most popular post since I started this blog in 2013.

While the truth about what power straps can potentially do if improperly adjusted is shocking, the lack of support in principles of applied science for the basic premise that I describe as indiscriminate envelopment as the approach to achieving a fit of a ski boot with the foot and leg of the user with the objective of substantially immobilizing it’s joints with unknown consequences, is even more shocking. Little or no consideration appears to be given to the effects of indiscriminate envelopment on the balance and motor control systems of the skier.

What is done to the foot and (lower) leg can affect the entire body. In his post, Foot biomechanics is dead. Discuss (2.), Professor Chris Nester states:

The foot is not a compilation of interconnected mechanical components that respond precisely to the laws of mechanics. It is a complex matrix of at least 11 biological tissues (i.e. skin, fat, muscle, tendon, joint capsule, ligament, bone, cartilage, fascia, nerves, blood vessels….) that responds to external loads through the symbiotic relationship between the motor control system and tissue properties.

Professor Nester goes on to state:

I believe the integration of our current foot biomechanics knowledge with insights from motor control, neurophysiology and related domains (e.g. tissue biology) will drive advances in foot function more than pursuing a pure mechanics paradigm.

Professor Nester proposes that the term biomechanics be replaced with the term Neurobiomechanics. I concur.

How Does the Ski Boot Affect the Human Performance of the Skier?

The short answer is that when the structures of a ski boot indiscriminately envelop the structures of a foot and a portion of the leg (aka the Perfect Fit or the Holy Grail), no one knows. While it is essential that a ski boot create a secure connection of the foot of a skier with the ski, it should not achieve this connection at the expense of natural neuromuscular function, especially balance.

In 1980, when I was about to prepare a new pair of Lange race boots for Steve Podborski, I asked myself whether it was possible to obtain a secure connection of the foot with the ski without compromising natural neuromuscular function or, even better, was it possible to enhance natural neuromuscular function?

I took a significant step towards answering this question in 1980 when I designed and fabricated a device I called a Dorthotic. The Dorthotic supports the upper or dorsal aspect of the foot as opposed to supporting the plantar aspect (i.e. the arch). My theory that loading the top of the foot or dorsum with a force perpendicular to the transverse or medial-lateral plantar plane of the foot has positive benefits for motor control and balance has begun to be recognized. The Dorthotic enabled Steve Podborski to compete and win on the World Cup Downhill circuit mere months after reconstructive ACL surgery and to eventually win the World Cup Downhill title, a feat no non-European has repeated. US and international patents for the dorsal device were awarded to me (David MacPhail) in 1983.

The success of the Dorthotic gave me a start towards answering the question of whether a secure connection of the foot with a ski was possible without compromising natural neuromuscular function. But I knew that I needed to learn a lot more. I realized that finding the answers I was seeking and especially unraveling the secret that enables the world’s best skiers to stand and balance on their outside ski, would require a multi-disciplinary approach.

The Missing Factor in Skiing: A Multi-Disciplinary Approach

A significant influence that served as the impetus for the design of the Birdcage research vehicle and the on-snow studies, was the work of Dr. Benno Nigg. In 1981, Dr. Nigg accepted an invitation to move from ETH Zurich, where he was the director of the biomechanics laboratory, to the University of Calgary, where he founded and developed the Human Performance Laboratory (HPL), a multi-disciplinary Research Center that concentrated on the study of the human body and its locomotion.

The publication of the Shoe In Sport in English in 1988 served as a seque to introduce me to Nigg’s research at HPL. Studies done at HPL found that any interference with the function of the human foot, even a thin sock, extracts a price in terms of the adaptive process the human body has to undergo to deal with what is really an externally imposed disability.

The Effect of Footwear on the Neuromusculoskeletal System

There is an excellent discussion in a recent post on the Correct Toes blog (3.) on the impact of a narrow toe box, toe spring and elevated heel of traditional footwear on the human body. Elevating the heel in relation to the forefoot will predictably cause a realigment of the ankle-knee-pelvis joint system with a corresponding adjustment in the tension of the associated muscles with a global effect on the Neuromuscularskeletal System. This has been known for decades. Elevating the heel in relation to the forefoot, will cause the ankle joint to plantarflex (reduce dorsiflexion) in relation to the support surface under the foot in order to maintain COM within the limits of the base of support.

Ramp Angle Rules

Due to the unstructured nature of the indiscriminate envelopment characteristic of the fit of the majority of conventional ski boots, it is extremely difficult, if not impossible, to determine the effect of constraint of this nature on the Neuromusculoskeletal System. So I’ll focus on the one aspect of the ski boot that has consistent and profound implications on skier human performance, especially motor control and balance; boot board ramp angle or zeppa. Binding ramp angle or delta compounds any effect of zeppa. For the sake of simplicity we’ll assume zero delta.

Contrary to the widely help perception, raising the heel of a skier in a ski boot does not cause CoM to move forward. In fact, it usually has the exact opposite effect. It puts a skier in the back seat with the weight on their heels. Worse, it can disrupt the competence of the biokinetic chain that dynamically stabilizes and protects the joints of the lower limbs. Excessive heel elevation can render a skier static and cause the balance system to resort to using the back of the shaft as a security blanket.

As of this writing, I am unaware of any standard within the ski industry for zeppa. It appears to be all over the map with some boots having as much as 6.5 or more degrees. The default zeppa for the human foot on a hard, flat level surface, is zero.

Through subjective experiments in 1978, I arbitrarily determined that zeppas in excess 3° had a detrimental affect on skier balance. In 1991, zeppas of 2.3° and 2.5° were chosen for the large (US 8-12) and small (US 4-8) Birdcages based on an analysis of the effect of ramp angle on COM and neuromuscular activity. This range appears to work for a majority of recreational skiers. But recent tests with a dynamic ramp angle assessment device that I designed and fabricated is finding the stance of elite skiers optimizes at much lower zeppa angles, with some skiers below 1.5°. Interestingly, when NABOSO insoles are introduced for the assessment, zeppas decrease even further. With minimal training, most skiers are sensitive to dynamic changes in zeppa of 0.1 degrees.

Implications for the future of skiing

A tectonic shift is underway on a number of fronts (see A Revolution) that is challenging the mechanical and static premises that form the underpinnings of the key positions in ski teaching and the design of equipment such as ski boots and the fit process. In my next post I will post recent material by Dr. Emily Splichal, functional podiatrist and inventor the revolutionary NABOSO small proprioceptive stimulating insole.



As I was in the process of writing this post, a FaceBook group on skiing posted a link to an article From PSIA: Examining Transitions. The article is based on a presentation last fall by US Ski Team Head Men’s Coach, Sasha Rearick, in which he shed new light on transitions (1.).  While Rearick did shed light on some events associated with transitions, as with previous efforts by others on this subject, Rearick failed to shed light on the mechanics and physics associated with edge change.

As I explained in my last post, transferring the weight from the outside foot and ski of a turn to the inside foot and ski in the transition phase sets in motion what I call the Eversion/Internal Rotation Cascade that rotates the base of the ski into a transient moment of full contact with the surface of the snow between changing to the new (downhill) edge.

At the start of the transition leading up to ski flat between edge change, the center of pressure (COP) of the weight of the body applied by the sole of the inside foot will be under the heel where it is aligned on the proximate center of the ski. In this configuration, the force applied to the ski by the skier is working with gravity to rotate the ski.

The post left off by showing how rotational inertia will tend to make the ski continue rotating about the uphill edge past ski flat and penetrate into the snow surface on its downhill aspect as shown in the graphic below.

Rotational inertia will tend to make the inside edge of the new outside ski automatically rotate into the turn except for the fact that the force FW applied by the skier is on the wrong side of the new edge.

The graphic below has a dashed red reference that is parallel with the snow surface.

If the force FW applied by the skier is still aligned on the transverse center of the ski, it act will act to oppose edge change as shown in the graphic below. When the axis of rotation of the body of the ski changes with a change in edges, the transverse aspect of the base of the ski and the platform under the skier’s foot will tend to accelerate into an eversion translation. But this can only happen if the associated biomechanics are not interfered with by the structures of the ski boot.

The graphic below shows the change in the mechanics of rotation associated with edge change.

At the start of the transition, movement of the mass of the skier’s upper body is in phase with the downhill rotation of the ski and the force FW applied to it. But when the ski changes pivots at edge change and the mass of the skier continues to move downhill, the force FW applied to the ski will tend to rotate it back to ski flat; i.e out of the turn, unless the point of application of force FW changes during ski flat as shown in the graphic below and COM of the skier is aligned with force FW.

………. the angle between the platform and force you apply to it, the platform angle, must be 90 degrees or smaller.  – page 19, The Ski’s Platform Angle, Ultimate skiing; Le Master

The shift in center of pressure from the heel to the ball of the foot in a turn sequence seen in pressure studies of expert skiers is well documented (2., 3., 4). What the studies are really confirming is the use by expert skiers of the Two Phase Second Rocker mechanism to rock (tip) the outside ski on edge and control the edge angle during the load phase of a turn sequence.

Since the limit of the position of the application of force by the foot in relation to the inside edge of the outside ski is the center of the ball of the foot the effect of ski width underfoot and stand height should be obvious. Both rotational inertia and torque will increase as the width of a ski underfoot (profile width) is reduced and stand height increased. When Ligey says he creates pressure, he is creating far more than just pressure.

While LeMaster appears to recognize the importance of a platform angle less than 90° for edge control and, to some degree, the effect of stand height, the explanation offered for superior edging is that this can be attributed to waist width and stand height making skis more like ice skates.In my next post, I will discuss the role of Turntable Rotation in setting up a platform under the body of the outside ski for a skier to stand and balance on while maintaining edge angle.




One of the most important events in the turn sequence is edge change. Yet, it is rarely mentioned in technical discussions. One of the few references I was able to find on edge change is in the CSIA Technical Reference which states:

Edge Change = Balance Change: Changing edges requires a change of balance.

Edge change occurs during an unbalanced, controlled fall in the transition phase that leads to the development of a balanced position on the outside ski as it crosses the fall line in the bottom of a turn. Properly executed, edge change leads to the development of a platform under the outside ski for the skier to stand and balance on.

The edge change sequence starts in the transition phase when a skier begins to transfer weight from the outside (downhill) ski to the inside (uphill ski). At the start of the transition, the edges of the inside ski are uphill and on the lateral (little toe) side of the foot. From a perspective of the gait cycle, the base of the ski is inverted (turned inward towards the center of the body). This is the normal configuration when the foot is unweighted in the gait cycle. The foot strikes the ground on the lateral (little toe) side and rotates about it’s long axis in the direction of eversion to bring the three points of the tripod of the foot into contact with the ground. As the foot everts, the leg rotates internally through torque coupling in the subtalar joint. The normal kinetic flow from foot strike to the support phase in mid to late stance is one of inversion of the foot/external rotation of the leg to eversion of the foot/internal rotation of the leg. Put another way, the human lower limbs will naturally rotate into a turn so long as the biomechanics are not interfered with.

At the start of the transition leading up to ski flat between edge change, the center of pressure (COP) of the weight of the body applied by the sole of the inside foot will be under the heel where it is aligned on the proximate center of the ski.

The Eversion/Internal Rotation Cascade

Transferring the weight from the outside foot and ski to the inside foot and ski in the transition phase sets in motion what I call the  Eversion/Internal Rotation Cascade. When the cascade starts, the force F W applied to the ski by the foot  by the weight of the body will impart rotational inertia as the ski rotates about the pivot point formed by its inside edge.

For the sake of simplicity, the stack of equipment between the sole of the skier’s foot and the snow is represented by a rectangle in a 3:2 ratio where the stand height is 50% higher than the width (FIS maximum stand height = 93 mm – maximum profile width = 63 mm). Sidecut is also not shown.

The following graphics show the sequence of the Eversion Cascade. Note: Internal rotation of the leg is not shown in this sequence.

The first graphic below shows the moment or torque arm ma that is set up by the offset that exists between GRF from the firm piste acting at the inside edge and the point where the center of pressure of the weight of the body acts in the plane of the base of the ski. The large red arc shows the radius of rotation. The small red arc shows the radius of the moment of force. In this sequence, the ski is rotating downhill away from the pivot at the uphill edge.

When the base of the ski comes into full contact with the surface of the snow, rotational inertia, will make it want to continue rotating about the uphill edge and penetrate into the snow surface on the downhill aspect. If the force FW applied by the weight of the body is still aligned on the transverse center of the ski, it will oppose edge change.

In my next post I will discuss how the Second Rocker affects the mechanics of edge change at ski flat.



A recent post on the Foot Collective Facebook page titled, Are you stable on 1 leg?, advises that if  you stand on one leg and look like the top row of pictures in the graphic below (red X), you have a foot & hip that are dysfunctional. This test is best done barefoot on a hard, flat, level surface.

Graphic with permission of Correct Toes

The lower photo (green checkmark) shows the alignment of a leg that is torsionally balanced (stiffened) in the ankle and knee joints. The foot and knee cap align straight ahead and square with the pelvis while the alignment of the knee with the foot, leg and thigh is substantially linear. If you can move to single limb support from two feet, easily achieve this alignment with minimal effort, sustain it for 30 seconds or more, and achieve similar alignment on both left and right legs, you probably have good stability in single limb support.

If you look like the upper photo (red x), it indicates dysfunction and especially a lack of torsional stability in the support limb. The problem is usually caused by constrictive, supportive, cushioned footwear and/or arch supports that, over time, deform feet and weaken the arches. Ski boots are one of the worst offenders in this regard.

If you and when you can achieve good stability in single limb support, you are ready to test the effect of footwear, especially your ski boots. Start by putting on your day to day footwear. Then do the same test on the same surface with each pair of shoes. Work your way up to your ski boots. Adjust the closures of your ski boots to the tension you normally set for skiing. If you are not able to quickly and easily assume the stable position shown in the lower photo (green checkmark), then you know that cause  is the footwear. You can then test the effects of insoles, including ski boot footbeds by removing them from the footwear, placing them on the test surface and moving to single leg support. While not perfect, these tests will help determine the cause of single support limb instability.

In skiing, an unstable outside support leg is characteristics of most skiers and even racers at the World Cup level. It is typically caused by ski boots interfering with the physiological processes that fascially tension the arches and forefoot that create the triplanar torsional stability of the ankle and knee joints of the biokinetic chain necessary to set up a platform under the outside ski to stand and balance on. But instead of addressing the underlying cause, the ski industry invented the term, knee angulation. Knee angulation is indicative of unbalanced torques acting about the uphill edges of the skis, especially the outside ski. When unbalanced torques are present about the edges of a skis or skis, unbalanced torques will also be present across the joints of the lower limb; not a good thing.

The alignment of the knee illustrated in the lower image (green checkmark) is seem as skier or racer enters the fall or rise line with outside leg extended, confirms the existence of a platform under the outside foot on which the skier or racer is balancing on with dynamic balance of torques across the joints of the ankle foot complex and knee. See my post MIKAELA SHIFFRIN AND THE SIDECUT FACTOR –

There is an abundance of information on programs to correct foot deformities,  muscle weakness and imbalances on web sites, YouTube and FaceBook groups such as The Foot Collective, Correct Toes, Feet Freex and the Evidence Based Fitness Academy – EBFA (Dr. Emily Splichal).

The Foot Collective web site has a series of posts on An Introduction to Feet and Footwear (1.) as well as a series of Foot-Casts (2.)

Meantime, a post on a web site called Rewire Me (3.) has an interview with Dr. Emily Splichal called No Shoes Allowed in which she discusses the importance of sensory information entering the body and the need to be able to process this information and handle the load and impact. Dr. Splichal suggests starting the process by getting the body and foot accustomed to sensory information without shoes acting as a barrier.

An excellent free paper with great graphics is The foot core system: a new paradigm for understanding intrinsic foot muscle function (4.)