sports science

THE FUTURE OF THE SKI BOOT – PART 2

The introduction of the rigid shell ski boot served as a foundation for the evolution of what became a science of immobilization and splinting of the joints of the foot and a leg of a skier. By creating an encasement for the foot and the portion of the leg within the rigid shell, mediums such as foam could transfer force to the ankle and leg to substantially immobilize its joints. Supporting the foot in a neutral position with a rigid footbed or orthotic in conjunction with form fitting mediums ensures maximal immobilization that is described as the Perfect Fit. The science of immobilization has evolved over the years to include thermoformable liners and even thermoformable shells.

Even though the medical textbook, The Shoe in Sport, cautioned 30 years ago that “the total immobilization by foam injection or compression by tight buckles are unphysiologic (against physiologic function)” the proponents of immobilizing the joints of the ankle continue to claim that this puts the foot in it’s strongest position for skiing.

The paper, Recent Kinematic and Kinetic Advances in Olympic Alpine Skiing: Pyeongchang and Beyond,  published on February 20, 2019, cited better transfer of the skier’s action to the skis through improved boot-fittings with individual liners and insoles. If in fact, skier performance is improved due to improvements in the science of immobilization through boot-fitting then it should be evident in studies that look at skier performance.

One such study, Challenges of talent development in alpine ski racing: a narrative review, published in March of 2019 found:

Youth and adolescent ski racers report lower injury rates compared to World Cup athletes. The knee was the most affected body part in relation to traumatic injuries. The most frequently reported overuse injuries were knee pain (youth) and low back pain (adolescent level). Athlete-related modifiable risk factors were core strength, neuromuscular control, leg extension strength and limb asymmetries.

Neuromuscular Function (NMF) affects Neuromuscular control (NMC). NMC is an unconscious trained response of a muscle to a signal associated with dynamic joint stability. This system of sensory messages (sometimes referred to as “muscle memory”) is a complex interacting system connecting different aspects of muscle actions (static, dynamic, reactive), muscle contractions, coordination, stabilization, body posture and balance. The movements of the lower extremity, including the knee joint, are controlled through this system, which needs correct sensory information for accurate sequential coordination of controlled movement.

It has been known for decades that restricting the action of a joint or joint system, especially immobilizing the joint, will cause the associated muscles to atrophy. But a study, Effect of Immobilisation on Neuromuscular Function In Vivo in Humans: A Systematic Review, published in March 2019, suggests that the effects of immobilizing joints of the body are far greater than simply causing muscles to atrophy. This is the first systematic review to consider the contribution of both muscle atrophy and deterioration in neuromuscular function (NMF) to the loss of isometric muscle strength following immobilisation. The fact that the study, Challenges of talent development in alpine ski racing: a narrative review, cited core strength and neuromuscular control as issues in the development of talent is significant. The feet are part of the core in what is called foot to core sequencing. Immobilizing the joints of the foot can affect lower limb and core strength.

Immobilisation in the study the Effect of Immobilisation on Neuromuscular Function In Vivo in Humans: A Systematic Review, was achieved by using casts, braces, slings, unilateral suspension, strapping or splints with the following locations immobilised: knee, ankle, wrist and finger. All studies measured isometric muscle strength. No studies were cited that involved bilateral immobilisation of both ankles such as occurs in form-fitting ski boots. However studies did find that multiple joint immobilisation was likely to produce the largest change in the NMF of segments consisting of both mono and biarticular muscles. Other key findings were:

  • The greatest changes in all variables occur in the earliest stages of immobilisation.
  • The loss in muscle strength during immobilisation is typically greater and occurs faster compared to the loss of muscle volume.
  • The choice of joint angle for immobilisation using the brace or cast method appears likely to play a large role in the outcomes.

I started this blog six years ago for several reasons. A primary reason was to identify whether any influences existed in skiing that would serve to change the focus from immobilizing the joints of the foot and leg with the associated claims to a science-based focus. Since the future of the ski boot appears to be continued refinement of the science of immobilization this will be my final post.

I have learned a lot over the past six years that led to huge breakthroughs on skis for myself and those who I have worked with. Thank you to those who commented and contributed to The Skier’s Manifesto.

THE FUTURE OF THE SKI BOOT – PART 1

SHOEspiracy, a new feet-first documentary by barefoot/minimal shoe maker Vivobarefoot (1.) provided me with insights on the factors behind the unproven theory on which the design and modification of the rigid plastic ski boot is based that supporting and immobilizing the foot of a skier in neutral places it in the strongest position for skiing.

The intent of SHOEspiracy is to shed light on what amounts to a  ‘Shoe-shaped’ Public Health Scandal’.

There is a 20 billion pair a year, silent public health scandal a’foot and it’s shoe shaped!

It’s astonishing to us that the vast majority of shoes produced each year are actually bad for people’s feet—and the wearers are none the wiser.

VIVOBAREFOOT co-founder Galahad Clark

According to the documentary SHOEspiracy is intended to inspire viewers to reconnect with their feet and create a drive within the multi-billion-dollar footwear industry to establish a template for healthy shoes, healthy feet and natural movement. Most people are blissfully unaware of the problems footwear can and does cause and assume that what they put on their feet is benign.

I commend Galahad and Asher Clark and Vivobarefoot for taking the initiative to educate consumers on the problems shoes can and do cause and to establish a template for shoes that respect and accommodate the physiologic requirements of the user.

From Function to Fashion

At one time all humans were barefoot. This changed about 40,000 years ago when humans began to wrap animal skins around their feet to protect them against damage from the elements.  From crude beginnings as nondescript forms of protection, footwear evolved into a fashion entity; one that changed the shape and appearance of the foot, often radically, to render it more aesthetically pleasing. Heels first appeared in horsemen’s shoes as a device to help keep the rider’s feet in the stirrups.

As the evolution progressed shoes became corrective and lifestyle devices in addition to fashion accessories. In the footwear fashion era people have historically worn shoes that deformed their feet, the Chinese Lotus shoe  being an extreme example. But since a degree of deformation does not typically result in a noticeable impact on low-key locomotion the negative impact of restrictive footwear has generally flown under the radar unnoticed.  Adverse effects due to footwear such as joint and muscle pains and impaired balance are usually attributed to other factors.

Young feet are especially malleable. Their shape can be molded by footwear often resulting in permanent deformity as mine were when as a child my feet were put in orthopedically correct, supportive footwear to help them develop properly. The recent photos below show the state of my feet after more than 5 years of wearing exclusively minimal shoes, doing exercises like the short foot and using NABOSO insoles. Although they have become much stronger and healthier, it is doubtful whether the damage done when I was a child can ever be undone.

The left hand photo shows my feet with forefoot minimally weighted. The right hand photo shows my feet weighted. Note the difference in the robustness of the big toe of my left foot compared to the big toe of my right foot. I believe this at least partially explains why I am able to stand and balance with superior stability on my left foot compared to my right foot.

The photos below serve to graphically illustrate why I gave up road biking several years ago and now ride a touring bike with large flat platform pedals and minimal shoes fit with NABOSO insoles. As my feet became stronger and more functional I was no longer willing to abuse them with constrictive footwear.

The Jogging/Ski Boot Connection

About 50 years ago a new type of shoe appeared; one that would revolutionize the footwear market. The Sports Shoe was created in response to the running boom of the 1970’s. When I took up running on the cusp of the running boom, runners of the day ran in flats made for tennis or basketball. These were plain canvas shoes with no heel toe drop or special features.

Jogging, published in 1967 by Nike cofounder, William J. Bowerman, served as a catalyst for the running boom that emerged in the 1970s and with it the development of jogging and other sports footwear including plastic ski boots. At the time that he wrote Jogging Bowerman was working with elite runners looking for ways to improve their performance. His book was preceded by the introduction of the first Lange ski boot in 1962 followed by a racing model in 1965.

People who took up jogging who hadn’t run before started having problems with their Achilles tendon and calf muscles because their everyday shoes had heels. After consulting with doctors Bowerman made a decision to raise the heel of his jogging shoes by 1/2” (12 mm) to accommodate people who wore dress shoes. This feature was for the general public, not the athlete. Bowerman recognized that the sports footwear industry needed to create a consumer product that could be worn without causing discomfort. In an attempt to address problems caused by raising the heel the sports shoe industry responded by adding counters, arch supports and other features; in effect adding band aids in an effort to correct problems caused by raising the heel.

When the Nike Waffle Trainer was marketed as a shoe designed specifically for jogging the idea of sport specific shoes initially made sense to me. But even though I had been running with a heel strike technique in flats I experienced problems right away with ankle and knee shock at heel strike in my Nike Waffle Trainers. In comparing the Nike shoe to my canvas flats it became obvious to me that the flared heel was adversely altering the mechanics of heel strike. Trimming away the outer (lateral) and rear aspects of the flared heel reduced the shock of impact at heel strike.  I suspected that other aspects of the shoe were also adversely affecting my running mechanics. This incident caused me to question whether the design of sport specific shoes was supported by science.

When I started looking for answers I found out that it had been known for decades that footwear can negatively impact the physiologic function of the user. But the issue of the effect of footwear on athletic performance came into sharp focus in 1989 with the publication of the medical textbook, The Shoe in Sport (published German in 1987 as Der Schu im Sport). The Shoe in Sport brought together the collective expertise of 44 international authorities on orthopedics and biomechanics to focus their attention on the SHOE PROBLEM in the context of problems shoes can cause for athletes that compromise performance and contribute to injury. The Shoe in Sport focusses on the medical and orthopedic criteria of sports shoes in offering guidelines for the design of shoes for specific athletic activities including skiing and ice skating. The efforts of the Shoe in Sport was supported by the Orthopedic/Traumatologic Society.

In the Introduction to the Shoe in Sport, Dr. med. B. Segesser and Prof. Dr. med. W, Pforringer note that the buyers of athletic shoes are always looking for the ideal shoe. In their search 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 directed at athletes from every angle.

Segesser and Pforrineger go on to state that the findings in the textbook should enable the interested reader to distinguish between hucksterism and humbug on the one side and scientifically sound improvements in the athletic shoe on the other. The Shoe in Sport makes it abundantly clear that it is not a question of if the structures of footwear will affect the physiologic function of the user but a question of how they will affect the physiologic function of the user and especially whether the footwear will compromise athletic performance and/or contribute to injury. The Shoe in Sport studies the biomechanical, medical and technical aspects of the shoe problem as it exists in various fields of athletic endeavour.

A number of leading footwear company executives have often said to me over the years that they know science and agree with the philosophy behind the benefits of barefoot shoes, but that consumers aren’t ready. – Galahad Clark

Clark’s statement seems to suggest that little has changed since the publication of The Shoe in Sport in 1987 and the subsequent publication of Nigg’s Biomechanics of Sports Shoes in 2010. One reason may be the difficultly in conducting objective studies that lead to definitive conclusions pertaining to effects on the user of specific features of footwear.

After I learned of the research done by Benno Nigg at the Human Performance Laboratory at the University of Calgary that found that anything appended to the human foot compromises physiologic function I set out to develop a minimal constraint device for rigid soled footwear such as hockey skates, ski boots, cycling shoes and the like that would create a functional environment equivalent to barefoot. Activities that employ rigid soled footwear are much easier to conduct in vitro and in vivo studies than other activities. The objective of the device I wanted to develop was to enable the study of the effects of interfering with the action of discrete joints or joint systems of test subjects by controlling variables against a standard reference. In 1991, I succeeded in developing such a device in a corroborative effort with a biomedical engineer. The device can be constructed at minimal cost and readily fit with instrumentation to capture performance data.

When I wrote my US patent 5,265,350 at the beginning of 1992 I described the research device in impeccable detail with the intent and hope that others would construct the device and conduct studies with it. Under the terms of a patent, research may be conducted using a technology for which patents are pending or granted without infringing. This meant that research vehicle could have been constructed and studies commenced as soon as my patent application was published.

The graphic below shows the Birdcage research device on the left and Figure 1 from US patent 5,265,350 published on  February 22, 1993 on the right.

Form follows Function

The designation of the research device as Figure 1 in the patent is symbolic of the priority I give to function and science over other considerations.

The design and development strategies used by David MacPhail are very holistic in nature, placing the human system as the central and most critical component in the biomechanical system. His intent is to maximize human performance and efficiency, while foremost preserving the well-being and safety of the users and minimizing biomechanical compromises.  Alex Sochaniwskyj, P. Eng.

In US 5,265,350 and subsequent patents granted to me I disclosed a series of accessories for use with the research device. I designed these  to enable the effect on the user of factors such as the position of key mechanical points of the foot in relation to the mechanical points of a snow ski appended to it to be studied. To the best of my knowledge the minimal constraint research device and accessories has yet to be constructed and employed by other parties.

…………. to be continued.


  1.  https://www.shoespiracy.tv

FOOTBEDS: THE UNKNOWN COST OF SUPPORTING THE ARCH OF A SKIER’S FOOT

Two recent studies (1.), (2.) question the merits of supporting the arch of a skier’s foot and especially any claims made that supporting the arch in neutral is the strongest position for skiing. 

It is well established in the scientific literature that the plantar aponeurosis (aka plantar fascia or PA) is one of the major arch-supporting structures of the human foot.  A positive correlation between Achilles tendon loading (ATF) and plantar fascia tension (PAF) has been reported. A study (3.) found that plantar aponeurosis forces (PAF) gradually increased during mid stance and peaked in late mid stance. The study found a good correlation between plantar aponeurosis tension (APF) and Achilles tendon force (ATF). The study concluded:

The plantar aponeurosis transmits large forces between the hindfoot and forefoot during the (mid) stance  phase of gait. The varying pattern of plantar aponeurosis force (PAF) and its relationship to Achilles tendon force (ATF) demonstrates the importance of analyzing the function of the plantar aponeurosis throughout the stance phase of the gait cycle rather than in a static standing position. – (my emphasis added in bold)

I discussed this in my post TRANSITIONING TO A HIGHER LEVEL OF SKIER PERFORMANCE.

The graphic below from Kevin Kirby’s Foot and Lower Extremity Biomechanics II:  Precision Intricast Newsletters, 1997-2002 illustrates how the position of COM in relation to the foot tensions the GS (gastroc-Soleus) compressing the arch which tensions the plantar aponeurosis ligament. I have added arrows to indicate PA strain Force F and Shear Force as well as Arch Compression Force.

The graphic below also from Kevin Kirby’s Foot and Lower Extremity Biomechanics II:  Precision Intricast Newsletters, 1997-2002 illustrates how the anterior (forward) advance of CoM in relation to the foot decreases rear foot loading (GRF-RF) and increases fore foot loading (GRF-FF). I have added a red dashed vertical line and a red triangle to show the approximate location of what would be what I term the tipping or pivot point where the foot would rock rearward and forward with a corresponding shift in CoM.

The two recent studies I referred to (1.), (2.) that question the merits of supporting the arch of a skier’s foot were actually done with subjects walking and running on flat and inclined surfaces. But the effect on arch compression is applicable to the effect of arch supports used in ski boots.

New Balance Minimus road MR00 shoes were provided to all participants to wear for testing (approx. weight 180 grams, zero heel-toe drop, no medial arch support and a uniform EVA midsole). Pockets filled with lead weights were affixed to the laces of both shoes in order to standardize foot weight across all shoe and insole conditions. The minimal shoe was chosen as a control condition in order to standardize non-insole effects as much as possible.

Two separate custom insoles were designed for each participant and fabricated by orthotic laboratory. The first insole was designed to restrict arch compression near-maximally compared to that during shod (barefoot) running (Full Arch Insole; FAI). The second insole was designed to restrict compression by approximately 50% during stance (Half Arch Insole; HAI). TO qualify for the study participants could not wear orthotics on a regular basis.

The study found:

The insert restricted maximum arch compression by approximately 70% when compared to unrestricted shod running and consequentially resulted in lower strain values throughout the entire stance phase. It should be noted that the PLF length only surpasses the estimated resting length between ~25%-80% of the stance phase in the insert condition (Fig 3). The negative strain values should be regarded as a slack PLF length, not as the PLF shortening beyond the resting length. 

The graphic below from the paper The Foot’s Arch and the Energetics of Human Locomotion shows the maximum arch compression of subjects shod barefoot (Shoe-only), with the Half Insole that restricted arch compression to 50% of the maximum amount and with the Full Insole that maximally restricted arch compression. The Full Insole is typical of insoles used to support the arch of a skiers’ foot.

 

The insoles had no effect on the metabolic cost of walking despite restricting ~80% of arch compression. 

In a personal communication with Sarah Stearne she advised me that the study didn’t measure muscle EMG activation with and without the insole but they did know that the ankle performed less positive (-8%) and negative (-10%) mechanical work when the insole was worn and that the ankle peak dorsiflexion moment was reduced (-7%). Based on the ankle moment and Achilles tendon moment arm data they calculated that there was ~6% less force in the Achilles tendon when the insole was worn.

Whilst several studies have acknowledged the elastic energy storage potential of the PLF, this ligament is primarily regarded for its role in providing integrity to the bony arch structure, and in supplying the rigidity required for the foot to function as a lever during propulsion (or skiing, my comment) 

This study confirms what I experienced in 1973 after I had full support custom orthotics made by a well known sports podiatrist. The orthotics felt comfortable standing on them and even walking. I experienced some discomfort when attempting to run with the orthotics in my jogging shoes. But when I tried skiing with them in my ski boots I felt as if my foot were floating on the top of the orthotic with little or no sensation of any force under my first MPJ.

Based on the results of two cited studies I believe there is no basis to assume that supporting the arch of a skier’s feet will have positive benefits or is without adverse consequences without first conducting comparative studies using standardized controlls (no insole, flat boot board) and established scientific protocols.


  1. The Foot’s Arch and the Energetics of Human Locomotion – Sarah M. Stearne1, Kirsty A. McDonald1, Jacqueline A. Alderson1, Ian North2, Charles E. Oxnard3 & Jonas Rubenson1,4 – (January 19, 2016)
  2. The Role of Arch Compression and Metatarsophalangeal Joint Dynamics in Modulating Plantar Fascia Strain in Running – Kirsty A. McDonald1, Sarah M. Stearne1, Jacqueline A. Alderson1, Ian North2, Neville J. Pires1, Jonas Rubenson1,3* – (April 7, 2016)
  3. Dynamic loading of the plantar aponeurosis in walking – Erdemir A, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA

THE FIRST SKI BOOT PROTOTYPE BASED ON THE BIRDCAGE

In going through archived files for the MACPOD Ski Boot Project I found a photo of the first injection molded ski boot prototype based on the principles of the Birdcage.

The photo below is of the Birdcage research vehicle that was used to validate my hypothesis that explained the mechanism by which elite skiers establish dynamic stability of the platform under the outside foot of a turn by balancing torques in two planes across the inside edge. This mechanism extends GRF acting along the running surface of the edge out under the platform for the skier to stand and balance on.

The photo below is of the Logan Chassis (aka The Convincer) that was developed in conjunction with the first injection molded ski boot prototype based on the principles of the Birdcage.

The photo below is of the first injection molded ski boot prototype. It was called the MACPOD boot. The design and format were very good. But the stiffness of the plastics, which were stiffer than used in conventional ski boots, was many orders too low on the scale of shore hardness. A subsequent effort called the Rise boot suffered from the same problem. It was a lack of suitable materials and manufacturing technologies that eventually sealed the fate of the MACPOD ski boot project.

TRANSITIONING TO A HIGHER LEVEL OF SKIER PERFORMANCE

The transition to a higher level of skier performance for my spouse and I started in the 2012-13 ski season. After a ten-year hiatus from skiing we were returning to the ski hills with renewed enthusiasm coupled with a desire to reach a higher level of performance. I purchased new narrow waisted skis for both of us. I intended to purchase new ski boots as well. But I quickly backed off from even considering this after assessing a number of new boots as too difficult to work with.

I started The Skier’s Manifesto in the spring of 2013 for a number of reasons. The primary reason was that the forum provided me with an opportunity to acquire new information and increase my knowledge so I could learn how to transition my spouse and I to a higher level of skier performance. The process of attempting to explain complex technical issues by writing articles and posts serves as the impetus for me to think deeply, thoroughly and analytically. As the process unfolded, I discovered issues I had overlooked in the past or not fully explored.

One issue I had not fully explored, let alone addressed, is a way of identifying the optimal ramp angle specific to each skier. Ramp angle is the angle of the ramp of the plantar plane under a skier’s foot with the base plane of the ski. Finding a method of identifying optimal ramp angle proved far more difficult than I had anticipated. But when I succeeded in identifying and then implementing the optimal ramp angles for my spouse and I last ski season this proved to be the gateway to a higher level of skier performance than I could ever have envisioned. After identifying and then confirming my optimal ramp angle as 1.2 degrees (bindings zero) I finally understood after almost 45 years how and why changing from the leather ski boots I learned to ski in to the new plastic boots had such a devastating impact on my skiing. It was the change in ramp angle. The ramp angle in my leather boots was much less than the ramp angle in my plastic boots.

By 1978 I had subjectively found that a ramp angle greater than 3 degrees adversely affects skier performance with some skiers affected more than others. I knew there was no one size fits all, only that more than 3 degrees seemed to cause problems. From 1978 onward I was improving skier performance by ensuring the total ramp angle of the combined boot board/binding (zeppa + delta) was about 3 degrees. For females with small feet this required grinding the boot board in Lange boots flat or even negative (heel down) to compensate for binding ramp angle which increased as the toe and heel pieces moved closer together for small boots. I wasn’t always able to get the ramp angle set at 3 degrees. But getting it in the 3 degree range consistently resulted in significant improvement in skier performance.

It was becoming increasingly apparent to me that finding the optimal individual ramp was critical.

Critical Ramp Angle

In 2018 I identified the critical ramp angle as the angle of the plantar plane in relation to the base plane of the ski that enables a skier to apply maximum vertical force to the ball of the outside foot when the COM in the pelvis is stacked vertically over the head of the first metatarsal.

The vertical force is applied passively by force transfered to the plantar aponeurosis ligament (PA) by Achilles tendon (AT) tension.  As COM moves forward towards the head of the first metatarsal in the support phase where skier resists the force of gravity, AT-PA tension applies an increasingly greater down force to the head of the first metatarsal. Ramp angle is optimal when the vertical force peaks just prior to the end of the support phase in what is called Mid Stance in the Gait Cycle of walking.  I qualified this mechanism as enabling a skier to apply maximum vertical force to the head of the first metatarsal. Studies have shown in the skiing the position of the pelvis in relation to its vertical position with foot is the most reliable indicator of the position of COM. A skier is able to control the vertical force applied to the head of the first metatarsal by controlling the position of the pelvis.

The photos below show Marcel Hirscher and Tesa Worley applying maximum force to the head of the first metatarsal of their outside foot by stacking their pelvis over it.

The Problem with Adapting

The primary determinant of the critical ramp angle is the length of skier’s Achilles tendon (AT).

The length of the AT can and does vary significantly among the general and skier populations. The type of everyday footwear worn and especially what is called drop (heel elevated above the forefoot) can affect the length of Achilles tendon.

Drop affects the timing of the process that stiffens the foot transforming it into a rigid lever for propulsion. Over time, the predominate wearing of footwear with significant drop can cause the AT to shorten as a way for the body to adjust the timing of the stiffening process. In activities such as walking and standing, a shortened Achilles tendon may not have a noticeable affect on performance. But in skiing, the timing of the AT-PA tensioning process is critical. Those who learned to ski in boots with ramp angles close to optimal for the length of their Achilles tendon typically excel at skiing regardless of athletic prowess while gifted athletes who learned to ski in boots with sub optimal ramp angle can struggle in spite of innate athletic ability. For a racer whose equipment is close to their critical ramp angle a change in equipment that significantly changes ramp angle can be fatal to a promising career.

Most skiers would assume that they can just adapt to a sub optimal ramp angle. But adaptation is precisely the reason why skiers and racers with a sub optimal ramp angle reach a threshold from which they cannot advance. When their brain makes repeated attempts to apply force to the head of the first metatarsal without success it starts to make adjustments in what are called synaptic connections to create a new movement pattern to adapt to sub optimal ramp angle. The more the equipment with a sub optimal ramp angle is used the more the associated synaptic connections are strengthened and reinforced. Once the movement pattern associated with sub optimal ramp angle is hardened,  optimal ramp angle is likely to be perceived by the brain as wrong. Telling a racer with sub optimal ramp angle to get forward or get over it (what that means) will only make matters worse because a sub optimal ramp angle makes it impossible. Correcting the ramp angle and/or the length of the AT will not help because neither will change the hard-wired movement pattern in the brain. Deleting a bad movement program can be done. But it usually takes a structured program and a protracted effort.

Mid Stance Misinformation

A factor that I believe may have contributed to the critical ramp angle issue being overlooked is misinformation about mid stance. The story used to sell footbeds and even some orthotics is that skiing is a Mid Stance activity and in Mid Stance the foot is pronated and weak necessitating a foundation under the arch to support it. While it is true that the load phase of skiing occurs in Mid Stance the statement that the foot is weak is only partially true because it doesn’t encompass the whole picture.

The Stance or Support Phase of what is called the Gait Cycle of walking consists of four phases:

  1. Loading Response
  2. Mid Stance
  3. Terminal Stance
  4. Pre-Swing

All four phases happen in a ski turn sequence. The support phase, where one foot is flat on the ground and the leg is supporting the weight of COM, is called Mid Stance. The position of COM in relation to the head of the first metatarsal in Mid Stance and how fast COM can move forward over the head of the first metatarsal (center of the ski) of the outside foot in the load phase is a major factor in dynamic control and the ability of a skier to apply maximum force to head of the first metatarsal. But Mid Stance is a range and a sequential stiffening process, not a fixed point as has been misrepresented for decades by many in the ski industry.

The graphic below shows the relationship of 1. Achilles Tendon Force with 2. Plantar Aponeurosis Force with 3. Vertical GRF and how the tensioning process and transfer of force to the head of the first metatarsal occurs as COM progress forward in the Mid Stance cycle. The timing of the forward advance of COM/Pelvis to sync with peak AT-PA force transfer to the head of the first metatarsal is shown with a red circle and vertical arrow.

If I had only shown the segment of Mid Stance in the grey rectangle at the beginning of Mid Stance on the left I could have made a case that the arch is weak and in need of support since Achilles Tension is zero and Plantar Aponeurosis Force (called strain) is very low. But this would be misinformation because it does not show the whole picture. If the foot were weak as is alleged it would be impossible for it to act in the capacity of a lever in propelling the weight of the body forward in locomotion.

In my next post I will explain how I used NABOSO surface science technology to confirm my optimal ramp angle.

 

TRANSITIONING FROM FIT TO HIGH PERFORMANCE FUNCTION


That footwear can negatively impact the physiologic function of the user has been known for many decades. But the issue of the effect of footwear on athletic performance came into sharp focus in 1987 with the publication of the medical textbook, The Shoe in Sport (published German in 1987 as Der Schu im Sport). The Shoe in Sport brought together the collective expertise of 44 international authorities on orthopedics and biomechanics to focus their attention on the SHOE PROBLEM in the context of problems shoes can cause for athletes in terms of compromising performance and contributing to injury. 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.

In the Introduction to the Shoe in Sport, Dr. med. B. Segesser and Prof. Dr. med. W, Pforringer state that the findings in the textbook 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. The Shoe in Sport made it abundantly clear that it is not a question of if structures of footwear will affect the physiologic function of the user, it is a question of how structures of footwear will affect the physiologic function of the user and especially whether they will compromise athletic performance and/or contribute to injury.

With regard to guidelines for ski boots, the international authorities on orthopedics and biomechanics who contributed their expertise and knowledge to Part IV The Ski Boot took the position that, among a number of other things:

  • ………. the total immobilization by foam injection or compression by tight buckles are unphysiologic.
  • The ski boot and it’s shaft must be adapted to the technical skill of the skier, and the technical skills of the skier must be adapted to the preexisting biomechanical functions of the leg and the foot.
  • It (the design) should not make compromises at the expense of other joints ………
  • It (the ski boot) must represent the ideal connecting link between man and ski (steering and feedback).

The position of international authorities on orthopedics and biomechanics on the medical and biomechanical criteria for ski boots was succinct, concise and unequivocal:

…….total immobilization by foam injection (implying by any means) or compression (of the foot) by tight buckles are (both) unphysiologic.

Dr. E. Stussi,  Member of GOTS and Chief of the Biomechanical Laboratory ETH, Zurich, Switzerland made a prescient statement with implications for the future of knee injuries in skiing:

Improvements in the load acting on the ankle (implying load from improved fit) make it biomechanically very likely that the problems arising in the rather delicate knee joint will increase.

While the international authorities on orthopedics and biomechanics who contributed to The Shoe in Sport provided valuable guidelines for the design of the ski boot they did not offer a specification that would assist designers and those who work with ski boots in meeting the medical and biomechanical criteria in the guidelines. My hope and intent was that the Birdcage studies and the content of my US Patent 5,365,350 (issued on 11-30-1993, expired on 12-28-2005) would serve as a foundation on which to build a specification that would enable the structures of ski boots to be adjusted to accommodate the personal functional requirements of the skier.

The steps in my transition from Fit to High Performance Function

After the unprecedented success of my dorsal loading invention with Crazy Canuck, Steve Podborski, I used the same system with similar success in the boots of a small number of other racers. I also incorporated this system into my own and my spouses’ ski boots in conjunction with suitable liner modifications and a reduction of the ramp angle of the boot boards to just under 3 degrees which I had identified in about 1978 as the maximum angle for skier performance.

I can’t recall exactly when, but about 20 years ago I decided to move away from Lange ski boots. I purchased a pair Head World Cup 335 mm ski boots for myself and a pair of Head X-80 295 mm ski boots for my spouse. I say built because to me ski boots are raw material.

I had to completely disassemble the Head X-80s and drastically modify and reconfigure the components to adapt them to the morphology of my spouses’ feet and legs. The process took me about 35 hours. I was able to modify my Head World Cup liners to make them work without the same degree of modification. I made a dorsal loading system for my spouse similar to the one I made for Steve Podborski’s Lange ski boots.  But I was able to modify the existing Head tongue so it would adequately load the dorsum of my foot. The reason I went this route is that the shell of my Head World Cup boot is very stiff. This makes inserting my size 12 US men’s foot and a dorsal system, like I fabricated for my spouse, challenging. In the order of things the dorsal system is inserted after inserting the foot in the shell.

The photo below shows my Head liner after initial modifications.

The photo below shows the Lange tricot liner I used in my spouses’ Head boots on the left with no modification other than removing the Lange flow fit pads in the side pockets. I was unable sufficiently modify the liner that came with her Head X-80 boot. The version on the right in the photo below is the same liner after modifications i made for it work with the dorsal system shown in the photo underneath. The dorsal system in itself took many hours of painstaking effort to fabricate and fine tune.

With our modified Head boots fit with my dorsal loading technology my spouse and I would easily be classified as expert skiers. As recreational skiers with skiing limited to 10-15 days a season, most skiers would have no incentive to question the adequacy of their boots or especially devote time and effort towards finding ways to reach a higher level of performance. To the contrary, I found it disturbing that the ability to ski better than the majority of skiers fostered an intoxicating sense of superiority. But I knew what I didn’t know and I knew that I still had a lot to learn. In my mind, the transition required to realise our full performance potential was not yet complete.  I knew that the potential for improvement has no boundaries.

The transition to High Performance Function continues In my next post……….

FIT VS. FUNCTION

With rare exceptions, the consistently stated objective of boot-fitting systems and modification efforts is to create a perfect fit of the foot and leg of a skier with the rigid shell of a ski boot by applying uniform force to the entire surface of the foot and the portion of the leg in the boot in what pits Fit against Function. The end objective of the Perfect Fit is to achieve a secure connection of the leg of the skier with the ski. In the name of achieving a secure connection of the foot with the ski, the function of the skiers’ foot has become unitended collateral damage.

But boot design and boot fitting effors didn’t start off with the intent of compromising the physiologic function of the foot. It just sort of happened as a consequence of the limited ability to change the shape of the rigid plastic ski boots to address issues of user discomfort when plastic boots were first introduced. The new plastic boots worked well for some skiers. But for most, myself included, my foot moved around inside the shell when I tried to ski. The feeling of insecurity created by the looseness made skiing with any semblance of balance or control impossible. The fix seemed to be a simple matter of trying to figure out where to place a pad or pads between the foot and shell to stop the foot from moving.

In 1973 when I first started tinkering with my own ski boots the craft of boot fitting barely existed. Like myself, those who were trying to solve the problem of a loose fit were doing proceeding by trial mostly with alot of errors. After what seemed like unending frustration from many failed attempts at trying to find and then solve the source of my loose fit, a consensus began to emerge within the ranks of the ski industry that the easiest and quickest solution was a process that would create a tight fit of the foot everywhere with the boot instead of wasting time trying to find the elusive right place to add pads. The Perfect Fit was born.

Injected foam fit was first off the mark as a Perfect Fit solution. But injected foam fit wasn’t tight or precise enough for my standards. So I tried to take the Perfect Fit to the next level with Crazy Canuck, Dave Murray. I started the process by carefully trimming and laminating together pieces of sheet vinyl to form a matrix of solid material that I inserted into the liners of Mur’s boots. The process took about 2 weeks of painstaking effort. Finally, I satisfied that Mur’s feet were securely locked and loaded; ready for the best turns of his life. The result? One of the world’s best racers was instantly reduced to a struggling beginner, the exact opposite of what I had expected! This experience served as a wakeup call for me; one that caused me to rethink what I thought I knew and question whether the Perfect Fit was the best approach or even the right approach.

I started looking for alternate ways to restrain the foot so it was secure in the shell of a ski boot without compromising foot function. In 1980 when I was building a pair of race boots for Crazy Canuck, Steve Podborski I literally put my finger on the solution when I pressed firmly, but not forcefully, on the instep of his foot just in front of the ankle and asked if he thought we should try holding his foot like this in his new race boots. Without the slightest hesitation he said, “That feels amazing. Let’s do it!”

It took me more several few days to fabricate a system to secure Pod’s foot in his boots by loading the area of the instep that I had pressed my finger on. The problem we faced when the system was finished was that the liner made it impossible to use the system without modifying it. So a decision was made to eliminate the liner except for the cuff portion around the sides and back of his leg which I riveted to shell. At the time I wasn’t sure the system would even work. So I made a pair of boots with fined tuned conventional fit as backup. A boot with no liner seemed like an insane idea. But Podborski was not only able to immediately dominate his competition on the most difficult downhill courses on the World Cup circuit but go on to become the first non-European to win the World Cup Downhill title. Even more remarkable is that in his first season on the new system he was able to compete and win less than 4 months after reconstructive ACL surgery.

What I discovered set me off in a whole new direction. Pressing on the instep of Podborski’s foot activated what I later found out is called the Longitudinal Arch Auto-Stiffening Mechanism of the Foot. This system is normally activated as the mid stance (support) phase of walking approaches late mid stance where the foot is transformed into a rigid structure so it can apply the forces required for propulsion. As I learned about the processes that transform the foot into a rigid lever I began to understand how interfering with the function of the foot can compromise or even prevent the Longitudinal Arch Auto-Stiffening Mechanism from activating and, in doing so, cause the structures of the foot to remain ‘loose’ regardless of any efforts made to secure it.  A rigid foot is necessary to effectively apply force to a ski.

The graphic below shows a sketch on the left from Kevin Kirby, DPM’s 2017 paper, Longitudinal Arch Load-Sharing System of the Foot (1.) Figure 44 A on the right is from my 1993 US Patent 5,265,350.

The above graphics clarify the details of the arch loading system I first disclosed in my US Patent 4,534,122. This system challenges the current Perfect Fit paradigm in which the physiologic function of the foot is compromised in an effort to try and achieve a secure connection of a skier’s foot with the ski.

Figure 44A above shows the principle components of the arch loading system which is comprised of a number of complimentary elements. I will discuss these elements in my next post which will focus on solutions.


  1.  Kirby KA. Longitudinal arch load-sharing system of the foot. Rev Esp Podol. 2017 – http://dx.doi.org/10.1016/j.repod.2017.03.003