Ski Equipment posts

TIGHTLY FIT SKI BOOTS COMPROMISE SKIER BALANCE AND CONTROL

In reviewing recent articles on ski boot fitting I encountered the same perfect fit of the boot with the shape of the foot and leg and ski boots must be tightly buckled for good balance and control narrative fabricated decades ago to justify the interference with the actions of the joints of the ankle and leg created by the rigid plastic shell ski boot.

When the first rigid shell plastic ski boots were introduced, the field of biomechanics, as it exists today, was in its infancy. Even until recently, the human foot was modelled as a rigid block which was consistent with the shoe last theory and the theory that the perfect fit of ski boots with the foot and leg of the user is the best option for skiing. Further support for the support and immobilize theory came from the vilification of pronation arising out of the misapplication of Root’s Neutral theory (1.)

By the time the authoritative medical text, The Shoe in Sport, was published in 1987, the knowledge of the biomechanics of the human foot had progressed to the point where tight-fitting ski boots and loading the ankle joint were recognized as unphysiologic.

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. (2.)

Investigations by Pfeiffer have shown that the foot maintains some spontaneous mobility in the ski boot. Thus the total immobilization by foam injection or compression by tight buckles are unphysiologic.(2.)

Many alpine skiers have insufficient mobility in their knees and ankle. The range of motion, particularly in the ankles, is much too small.(2.)

From a technical (skiing) point of view, the ski boot must represent an interface between the human body and the ski. This implies first of all an exchange of steering function, i.e., the skier must be able to steer as well as possible, but must also have a direct (neural) feedback from the ski and from the ground (snow). In this way, the skier can adapt to the requirements of the skiing surface and snow conditions. These conditions can be met if the height, stiffness, angle and functions (rotational axes, ankle joint (AJ)/shaft) of the shaft are adapted, as well as possible to the individual skier. (3.)

The articles on ski boots in the Shoe in Sport identified the objectives I was seeking in my efforts to design a ski boot based on principles of what is now referred to as neurobiomechanics. By the time I had formulated my hypothetical model of the mechanics, biomechanics and physics of skiing in 1991 I understood the need to restrain the foot in contact with the base of a ski boot and maintain the position of the foot’s key mechanical points in relation to the ski while accommodating the aspects of neurobiomechanical function of the foot and leg required for skiing. This was the underlying theme of the US patent that I wrote in February of 1992.

Existing footwear does not provide for the dynamic nature of the architecture of the foot by providing a fit system with dynamic and predictable qualities to substantially match those of the foot and lower leg. – US patent No. 5,265,350: MacPhail

On June 2, 2013 I published the post TIGHT FEET, LOOSE BOOTS – LOOSE FEET, TIGHT BOOTS (4.) in which I describe how attempts to secure the foot to a ski in a manner that interferes with the physiologic mechanisms that fascially tension and stiffen the structures of the foot that render it dynamically rigid actually reduce the integrity of the joint system of the lower limbs and hips resulting in a looser connection with the ski.

Studies done in recent years confirm the role of the active state of the architecture and physiology of the foot to postural control and balance.

These findings show that rather than serving as a rigid base of support, the foot is compliant, in an active state, and sensitive to minute deformations. In conclusion, the architecture and physiology of the foot appear to contribute to the task of bipedal postural control with great sensitivity. (5.)

The science of neurobiomechanics and the understanding of the mechanisms of balance and the role of the sensory system in human movement is accelerating. The time is long overdue for skiing to abandon it’s outdated concepts and align it’s thinking with the current state of knowledge.


  1. IS ‘SUBTALAR NEUTRAL’ SKIINGS’ HOUSE OF CARDS? – https://wp.me/p3vZhu-2mn
  2. 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
  3. Biomechanical Considerations of the Ski Boot (Alpine) – Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland
  4. https://wp.me/p3vZhu-2K
  5. Foot anatomy specialization for postural sensation and control

SKIER BALANCE: IT’S ABOUT BALANCING OPPOSING TORQUES

The subject of my 4th post published on May 14, 2013 was the role of torques in skier balance. That this was one of my most important yet least viewed posts at 109 views suggests that the role of torques in skier balance is a concept foreign to skiers especially the authorities in the ski industry. This post is a revised version supplemented with information results from a recent study on balance control strategies.


While everyone recognizes the importance of good balance in skiing, I have yet to find an definition of what is meant by good balance, let alone a description of the neurobiomechanical conditions under which a skier is in balance during actual ski maneuvers. In order to engage in a meaningful discussion of balance, one needs to be able to describe all the forces acting on the skier, especially the opposing forces acting between the soles of the feet of the skier and the snow surface (ergo – applied and ground or snow reaction forces). Without knowing the forces involved, especially torques, any discussion of balance is pure conjecture. In 1991,  I formulated a hypothetical model that described these forces.  I designed a device with biomedical engineer to capture pressure data from the 3-dimensional forces (torques) applied by the foot and leg of the skier to the internal surfaces of the boot during actual ski maneuvers.

Test subjects ranged from Olympic and World Cup champions to novice skiers. By selectively introducing constraints that interfered with the neurobiomechanics of balance even a World Cup or Olympic champion calibre skier could be reduced to the level of a struggling beginner. Alternatively configuring the research device to accommodate the neurobiomechanical associated with skiing enabled novice skiers to use  balance processes similar to those of Olympic champions. To the best of my knowledge, no one had ever done a study of this nature before and no one has ever done a similar study since.

When analyzed, the data captured using the device called into question just about everything that is accepted as fact in skiing. This study was never published. For the first time I will present the data and describe the implications in future posts. We called the device shown in the photo the Birdcage. It was fully instrumented with 17 sensors strategically placed on a 3 dimensional grid.

Birdcage

The Birdcage instrumentation package was configured to detect coordinated neuromuscularly generated multiplane torques that oppose and maintain dynamic balance against external torques acting across the running surface of the inside edge of the outside ski in contact with the source of GRF (i.e. the snow).

  1. plantarflexion-dorsiflexion
  2. inversion-eversion
  3. external/internal vertical axial tibial rotation

Ankle torques are applied to the 3 points of the tripod arch of the foot (heel, ball of big toe, ball of little toe) and can manifest as hindfoot to rearfoot torsion or twisting wherein the forefoot rotates against the rearfoot.

A recent study (1.) on the role of torques in unperturbed (static) balance and perturbed (dynamic) balance found:

During perturbed and unperturbed balance in standing, the most prevalent control strategy was an ankle strategy, which was employed for more than 90% of the time in balance.

In both postures (unperturbed and perturbed) these strategies may be described as a single segment inverted pendulum control strategy, where the multi-segment system is controlled by torque about the most inferior joint with compensatory torques about all superior joints acting in the same direction to maintain a fixed orientation between superiorsegments.

The alignment of opposing forces shown in typical force representations in discussions of ski technique is the result of the neuromuscular system effecting dynamic balance of tri-planar torques in the ankle-hip system.

NOTE: Balance does not involve knee strategies. The knee is an intermediate joint between the ankle abd hip and is controlled by ankle/hip balance synergies.

The ankle strategy is limited by the foot’s ability to exert torque in contact with the support surface, whereas the hip strategy is limited by surface friction and the ability to produce horizontal force against the support surface.

Ankle balance strategies involve what are called joint kinematics; 3 dimensional movement in space of the joint system of the ankle complex. Contrary to the widely held belief that loading the ankle in a ski boot with the intent of immobilizing the joint system will improve skier balance, impeding the joint kinematics of the ankle will disrupt or even prevent the most prevalent control strategy which is employed for more than 90% of the time in balance. In addition, this will also disrupt or even prevent the CNS from employing multi-segment balance strategies.

Regardless of which strategy is employed by the central nervous system (CNS), motion and torque about both the ankle and hip is inevitable, as accelerations of one segment will result in accelerations imposed on other segments that must be either resisted or assisted by the appropriate musculature. Ultimately, an attempt at an ankle strategy will require compensatory hip torque acting in the same direction as ankle torque to resist the load imposed on it by the acceleration of the legs. Conversely, an attempt at a hip strategy will require complementary ankle torque acting in the opposite direction to hip torque to achieve the required anti-phase rotation of the upper and lower body.

Balance is Sensory Dependent

As a final blow to skier balance supporting the arch of the foot and loading the ankle impairs and limits the transfer of vibrations from the ski to the small nerve sensory system in the balls of the feet that are activated by pressure and skin stretch resulting in a GIGO (garbage in, garbage out) adverse effect on balance.

Spectral analysis of joint kinematics during longer duration trials reveal that balance can be described as a multi-link pendulum with ankle and hip strategies viewed as ‘simultaneous coexisting excitable modes’, both always present, but one which may predominate depending upon the characteristics of the available sensory information, task or perturbation.


  1. Balance control strategies during perturbed and unperturbed balance in standing and handstand: Glen M. Blenkinsop, Matthew T. G. Pain and Michael J. Hiley – School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK – Royal Society Open Science

SCHEDULE OF POSTS

The link below will take you to a page with a link to a PDF of all 298 posts I have made since my first post of May 11, 2013.

https://wp.me/P3vZhu-2sM

The schedule lists posts in the order of newest (Jul 10, 2018) to oldest (May 11, 2013). The image below shows what the schedule looks like. The date and time of the post and the views and likes are listed below the title of each post.

 

The top 10 posts to date are shown in the graphic below.

I am in the process of reviewing and analyzing post subjects based on ranking with the objective of better directing my efforts to my readers. If there are any subjects you would like addressed please post them in the comments section.

 

SKI BOOTS: WHY LESS IS MORE

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

ZEPPA-DELTA ANGLE EXTENDER

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?

 

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 SHOCKING TRUTH ABOUT SKI BOOTS

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.


  1. https://wp.me/p3vZhu-UB
  2. https://talkingfeet.online/2018/01/18/question-3-foot-biomechanics-is-dead-discuss/
  3. https://www.correcttoes.com/foot-help/footwears-impact-musculoskeletal-system/