Footwear science posts

WHAT SHOULD A SKI BOOT DO?

After Steve Podborski won the 1981-82 World Cup Downhill title using a revolutionary dorsal fit technology I developed for his ski boots in June of 1980, he proposed that we become partners in a venture to develop a new ski boot that would do for every skier what the dorsal fit system had done for him. In exchange for my creative efforts, Podborski would fund the venture up to a point after which we would try to raise funds from investors for the project.

If I accepted Podborski’s proposal (which I eventually did), I knew the we faced significant hurdles. After giving the proposal a lot of thought, I accepted Steve’s offer. Steve and I became partners in a company called MACPOD Enterprises Ltd. While I had identified some of the pieces of the puzzle, I didn’t yet know the answer to the question what a ski boot should do. But I knew that when the time came to raise money I would need to provide investors with convincing evidence that I knew the answer to this question.

Podborski’s success lent credibility to the project. But his credibility was based on his subjective assessment supported by his race results. To be credible, a ski boot design based on principles of science would need to be supported with data from actual skiing maneuvers that could generate meaningful, quantifiable metrics for such things as balance and ski control. When the metrics were compared to the same metrics from data captured from the same skiers using conventional ski boots, they would need to unequivocally demonstrate superior performance of the MACPOD ski boot. I had to come up with a format that would satisfy potential investors that the new ski boot MACPOD would develop would be at least as good, if not better, than the system Podborski used to win the 1981-81 World Cup Downhill title. Whatever format I came up with had to be capable of allowing investors who skied to ski in it.

In 1992, MACPOD raised money from investors to fund the first phase of the venture. The pressure was on.

The single variable assessment protocol

The factor that convinced Podborski of the merits of my dorsal fit system was the comparison test he did against identical Lange boot shells fit with conventional Lange liners.

After rupturing his ACL testing skis at the end of July in 1980 Steve went to France 2 weeks before the opening downhill race of the 1980-81 World Cup season at Val d’isere to be with the team to support them. He had not planned on skiing, let alone racing, because he had been told by his doctors he was out of commission for the 1980-81 World Cup Downhill season. But Podborski had brought 2 pair of identical Lange boot shells to France with him just in case. One pair had the untested dorsal fit system with only the upper cuff of a Lange liner mounted on the boot shaft. The other pair had conventional Lange liners.  The only difference between the boots was the fit system; the classic single variable assessment protocol.

The graphic below from my US Patent shows a conventional tongue format (20) in FIG 3 (prior art) compared to my dorsal fit system (30) in FIG 5. The shin component (31) is like a conventional tongue.

On a whim, Podborski decided to see if he could ski in the boots with the dorsal fit system. He was amazed to find that he could ski well with little pain in his partially healed, reconstructed ACL. But when he tried to ski in the boots with the conventional liner he could barely ski.  I found this interesting because the impetus for the new fit system was my hypothesis that dorsal loading of the bones of the midfoot might reduce strain on the knee by dampening decompression of the arches resulting from perturbations in ground reaction force due to asperities and undulating terrain. A conventional liner could not be used because it would have interfered with the interface of the lower shell overlap closure on the upper surface of the dorsal fit system required to apply force to it. Fig 9 below from the patent shows how the overlap of the shell applies force to the upper surface of the dorsal fit system. The buckle closures allow the force, which should be minimal, to be regulated.

The ability to compare the dorsal fit system against a conventional liner system on the same day and in same conditions made the superiority of the dorsal fit system apparent. The unprecedented improvement in performance with no run-in period or special training program strongly suggested that the improvement resulted from reducing factors in conventional ski boots that limit or degrade human performance. This experience caused me to undertake a critical analysis of the functional requirements of the human system for skiing. This exercise opened the door to the possibility of technologies that would integrate external appendages such as skis and skate blades with the human system, what I later came to term Bio-Integration.

Bio-Engineering

If structures of ski boots, ice skates and cycling shoes can limit or degrade the human performance of the user it also became apparent to me that it might be possible to modify the function of the feet and lower limbs that would make it specific to activities such as skiing, skating or cycling and even potentiate neuromuscular function. I termed this concept Bio-Engineering. I didn’t realize until 1991 that the dorsal fit system used principles of Bio-Engineering.

The graphic below is the pressure image of the right foot of an elite cyclist showing the forces applied by the foot to the sole of the shoe on the pedal spindle at 3 o’clock in the stroke sequence at a low cadence with a moderate to high load on the crank. The cyclist is wearing a conventional rigid sole cycling shoe with no arch supports, wedges or other accessories.

Red is highest force. Dark blue is the lowest force. Forces were recorded with a Tekscan F Scan system fit to the shoe.

The highest force is applied under the ball of the great toe and the great toe and to a lesser extent, the second, third and fourth toes. The dashed line shows the approximate location of the pedal spindle which is the source of resistance/reaction  force. This pressure pattern is typical of elite cyclists. Ideally, the highest force should be applied across the width of the pedal spindle by the heads of all five metatarsals. Note that aside from the high pressure patterns on the ball of the foot and toes 1 through 4 the pattern is diffuse across the heads of metatarsals 2 through 5 and under the heel.


In my next post, I will show a pressure pattern of the same foot in the same position with a technology that Bio Engineers the foot and lower limbs and discuss the significant differences.

IN THE BEGINNING: HOW I GOT STARTED IN SKI BOOT MODIFICATIONS

I originally published this post on May 12, 2013. This is a revised and edited version.


Before I started ‘tinkering’ with ski boots in 1973, I didn’t just read everything I could find on the subject of fitting boots, I devoured every bit of information I could find on the subject. The assumption I made at that time was that the experts in the field not only knew what they were talking about, but that they also had the requisite knowledge and understanding of the underlying principles to back up their positions with applied science and/or research. Based on this assumption, I started modifying ski boots by doing all the things the experts recommended such as padding the ankle to ‘support’ and ‘stabilize’ it in the boot shell and cuff and adding cants between the soles of the boots and the skis to make the skis sit flat on the snow. But the big breakthrough for me came when I started making footbeds to support the foot.

Within a year I had gained expertise in my craft to the point that skiers from all over Canada were starting to seek out my services. In  response, I started a company called Anatomic Concepts. Soon, I was spending most of my free time working on ski boots. But while I was helping a lot of skiers ski better, none of what I was learning or doing was helping my own skiing. I was still struggling after switching from low-cut leather boots to the new stiff, all plastic boots.

The (Un)Holy Grail

Despite the inability to solve my own problems, my thinking remained aligned with conventional thnking right up until my experience with Mur and the ‘Holy Grail’ of ski boots; the perfect fit of the boot with the foot and leg of the skier.

In 1977, Roger McCarthy (head of the Whistler Ski Patrol), whose boots I had worked, on introduced me to Nancy Greene Raine in the Roundhouse on top of Whistler Mountain. The timing was perfect. Racers on our National Ski Team were having boot problems. They needed help. It was a classic case of me being in the right place at the right time. Nancy recruited me, flew me to Calgary at her expense and introduced me to the National Team and Dave Murray. She set up a working arrangement with the team, one in which I was completely independent. Nancy also introduced me to Glen Wurtele, head coach of the BC Ski Team. At Wurtele’s request, I began working on the boots of members of the team.

I started working on the boots of NAST (National Alpine Ski Team) racers with Dave Murray; ‘Mur’ as he was affectionately known. My thinking at that time vis-a-vis the need to immobilize the foot and achieve a ‘perfect fit’ of the boot with the foot was aligned with the approach of the  ‘experts’ in the  field. Mur didn’t live far from me. When I was working on his boots, he seemed to spend more time at our home than his. Because of my ready access to Mur, I saw an opportunity to achieve the Holy Grail of skiing with a fit of the boot with the foot so perfect that the foot was for all intents and purposes rendered rigid and immobile and united with the structures of the ski boot.

To achieve this lofty goal I spent the better part of 2 weeks working for hours every night carefully crafting a matrix of heat formable 1 mm thick vinyl around Mur’s foot and leg and the shells of his boots with my inserts inside the liners of the boot. When Mur finally confirmed he was ‘loaded, locked and ready’ he went skiing to test the results. I waited for the inevitable confirmation of success and certain celebration that would follow. But after what seemed like an eternity, instead of the expected good news, Mur called to tell me that he could barely ski with my perfect fit. He had little or no balance or control. The Holy Grail had reduced a world class skier to a struggling beginner. I didn’t need to be a rocket scientist to know that the industry had to be way off track especially in view of the recent publication of Professor Verne T. Inman’s seminal book, The Joints of the Ankle.

After this experience I knew that there was way more going on than I understood. I started learning about human physiology, in particular, about the mechanics, neuralbiomechanics and physics of skiing. I started asking hard questions that no one in the industry seemed to have answers for. And I started going off in a very different direction from the one the industry was acquiring increasing momentum in. If the perfect fit could impose what amounts to a severe disability on one of the world’s best skiers I could only imagine what such indiscriminate constraint was doing to the average recreational skier. It could not be good. For me it certainly wasn’t.

A major turning point came for me in 1988 when a husband and wife radiology team who had heard about my efforts to try and develop a ski boot based on anatomical principles presented me with a copy of a medical text called The Shoe in Sport published in German in 1987. This seminal work contains an entire chapter dedicated to The Ski Boot. I discuss the issues raised about the design and fabrication of ski boots by international experts in the articles in chapter on The Ski Boot in my most viewed post to date; THE SHOCKING TRUTH ABOUT POWER STRAPS (1.)

The Root of Misinformation

Unfortunately for skiing, the relevance and significance of the knowledge contained in The Shoe in Sport was overshadowed by the publication in 1971 of the book, the Biomechanical Examination of the Foot, Volume 1 by Drs. Merton Root, William Orien, John Weed and Robert Hughes. The book lists what the authors call their “Eight Biophysical Criteria for Normalcy”. These criteria, which have since been challenged and shown to be largely invalid,  were claimed to represent the “ideal physical relationship of the boney segments of the foot and leg for the production of maximum efficiency during static stance or locomotion”.

A key component of the biophysical criteria was that a bisection  of the lower third of the leg be perpendicular to the ground and the subtalar joint rest in neutral. Root described neutral as occuring when the subtalar joint was neither supinated or pronated.

In order to be considered normal, a foot had to meet all eight biophysical criteria. The effect of this criteria, which was arbitrary, was to render the majority of the feet of the world’s population abnormal and candidates for corrective interventions. Although Root never stated, implied or suggested it, his neutral sub-talar theory appears to have been misinterpretated in the ski industry to mean that the foot functions best in static ski stance when its joints are immobilized in neutral (sub talar).

In recent years, Root’s Sub-Talar Neutral Theory has come under increasing challenge with calls to discontinue its use (2.).

Conclusions
Taken as part of a wider body of evidence, the results of this study have profound implications for clinical foot health practice. We believe that the assessment protocol advocated by the Root model is no longer a suitable basis for professional practice. We recommend that clinicians stop using sub-talar neutral position during clinical assessments and stop assessing the non-weight bearing range of ankle dorsiflexion, first ray position and forefoot alignments and movement as a means of defining the associated foot deformities. The results question the relevance of the Root assessments in the prescription of foot orthoses.

The results of the wider body of evidence have the potential to have profound implications for skiing in terms of the application of Root’s Subtalar Neutral Theory as putting the foot in the most functional position for skiing by supporting and immobilizing it in neutral (subtalar).


  1. https://wp.me/p3vZhu-UB
  2. https://jfootankleres.biomedcentral.com/articles/10.1186/s13047-017-0189-2

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?

 

SKI BOOT ASSESSMENT PROTOCOL

Step 1 of the synergy 5 Step performance Program described in my last post is a Footbed Check using the Novel Pedar insole pressure analysis system.

Step 3 of the program is the Ski Boot Assessment detailed below. As with the 5 Step performance Program, the Ski Boot Assessment protocol and report were intended to serve as a template to base future programs on. The assessment report was intended to provide clients with information on the effects of their ski boots on their performance and/or as a work order for them to take to a boot-fitter to have any necessary issues identified in the report addressed.  Synergy Sports Performance Consultants Ltd. did not sell products or perform boot modifications.

 



My next post will be called FOOTBEDS: THE GOOD, BAD AND THE UGLY.

 

 

 

 

A FIVE STEP SKIER PERFORMANCE PROGRAM

Almost 40 years ago to the day, the head of the Whistler Pro Patrol, whose boots I had worked on, introduced me to Nancy Greene in the Roundhouse restaurant on top of Whistler Mountain. The rest is, as they say, history. Nancy asked me if I would work on her ski boots. She was so impressed by the results of my work that she approached the National Ski Team to make arrangements for me to work with some of Canada’s best racers.

Recently, while going through some archived files, I found copies of Nancy’s communication with the Program Director of the National Ski Team, Andrzej Kozbial. When Nancy approached me about working with our National Team, I stressed to her that I did not see any potential arrangement with the team as a job opportunity but instead as a vehicle where I could gain further experience and knowledge while providing a crucial service to the team and furthering the sport of skiing.

The graphic below is an excerpt copied from Nancy’s first letter of April 26, 1978 to the National Ski Team Program Director.

At the time that I wrote my US Patent 5,265,350 in early 1992, the intent and purpose of the detailed and lengthy specification was to provide a repository of the knowledge I had acquired to date to serve as a legacy for skiers and skiing to help advance the sport. While this information was in support of the inventions disclosed in the patent, the majority of the information was not subject to protection under the terms of the patent. The information was open access to the world. This was my intent.

In spring of 2000, I formed a company with 2 partners for the 2000-2001 ski season called Synergy Sports Performance Consultants Ltd. The objective of the venture was to gain further experience and knowledge and create a model that could be used as a template for future skier performance programs.

The following series of graphics are from Power Point presentations synergy made to ski schools.

The following graphic is the poster that described the synergy 5 Step Performance Program.

5 Step Performance Program description

The synergy Analysis Program looks at how your body interfaces with your ski equipment; primarily your footbeds and boots because this is the connection to your equipment and through it to the snow.

Synergy offers the program as a package made up of 5 components. They can either be taken as the complete package [recommended], several components or steps at once, or one component at time. Synergy recommends that you begin at step 1 and follow the sequence in numerical order. But the order can be arranged however you wish to suit your needs. The choice is yours.

1.Biomechanical Assessment

Good foot function is the key to control. That’s why the first thing we thing we assess is your biomechanical function. What that means is that we look at how well your foot and lower limb works. The examination is done by a podiatrist who looks at how your foot functions and how the lower limbs all connect.  Then we see how effectively your feet interface with the ground by putting you on insoles that read the pressures under your feet. We coach you through some balance movements while we watch how your foot functions while our computer records the results

2. Footbed Assessment

Footbeds can have a positive, neutral or negative effect on the function of your feet.

That’s why the next thing we check is how your foot interfaces with your footbed or orthotic.  We make sure that it allows your foot to function as well as it should without one.  And if your foot needs some assistance for optimal function we make sure the footbed is helping your foot do what it needs to do.

3. Ski Boot Assessment

Now that your foot is functioning optimally we make sure your ski boot lets it keep functioning. We conduct a thorough examination of your boot and provide you with a report that tells you how your boot is affecting your performance. Most important, we tell you what has to be done to fix the problem.

4. Kinesthetic Training

Skiing is about making the right moves. Kinesthetic Training is next. It teaches you how to tell when your body is making those moves. What is Kinesthetic Training? In simple terms it means to train your body to associate a feeling or sense with the right movements made at the right time. It is feeling and bringing about an awareness so you know when you are doing it right because we have taken you there and you have felt it. A picture may be worth a thousand words, but in skiing a feeling is worth a thousand pictures. We bring you to understand what you should feel in your foot at the start of the turn and then what it feels like to settle and balance onto the foot that drives the ski. By acquiring this sense you become more aware of how to allow your foot to transfer energy directly to the edge of the ski by using the body the way it was designed to be used. Remember, your body was not made to be a lever.

5. On-Hill Data Collection

This is where everything comes together. We move to the ski hill for this part of the package. We meet up top on Whistler or Blackcomb Mountain. We put our pressure insoles in your ski boots.  A pair of cables from the insoles goes up your ski pants where it connects to the data box [a kind of mini computer] we attached to your waistband.  Then we go out for a run on moderate, groomed terrain.  We record data in three takes in medium radius turns at a speed you are most comfortable with. While this is happening we videotape your skiing. Then we head into the lodge and synchronize the video with your foot pressure data. When this is done we watch your foot function in your boots on the computer screen on one side while we study your ski video on the other side of the screen. This way we confirm that your foot is functioning optimally as confirmed by analyzing your movement patterns and the timing of your skills.

My next post will be on the synergy Boot Assessment program.

 

THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: BALANCE PLATFORM MECHANICS

Turntable rotation generated by the powerful internal rotators of the pelvis (the gluteus medius and minimus) in combination with second rocker mechanics can create a platform under the body of the outside ski and foot that a skier can stand and balance on using the same processes to balance on solid ground. The associated mechanics creates a platform under the body of the outside ski by extending  ground reaction force acting along the portion of the inside edge in contact with the snow, out under the body of the ski.

In order to understand the mechanics, we need to start with a profile through the section of the body of the ski, binding and boot sole under the ball of the foot. The graphic below is a schematic representation of a ski with a 70 mm waist and 100 mm shovel and tail with an arbitrary length of 165 mm. The total stack or stand height from the base of the ski to the surface of the boot that supports the foot is 80 mm. The uppermost portion of the schematic shows the shell sidewalls of a 335 boot in relation to the 70 mm width of the stack. A ski with a 70 mm waist will place the center ball of the foot of skiers with US Men’s 10 to 12 feet close to over the inside edge. The heavy black line at the bottom of the stack shows the projection of the sidecut width beyond the waist.The schematic serves as a base on which to overlay a free body diagram showing the forces acting across the interface of the inside edge with the snow. This is where the rubber meets the road.

There are two possible scenarios in terms of the axis on which the center of pressure W of the skier will act. Unless the foot can sufficiently pronate and especially generate impulse second rocker loading, W will lie on the proximate anatomic center of the foot and transverse center of the body of the ski as shown in the graphic below. In this location, W will create a moment arm due to the offset with the GRF Pivot under the inside edge at the waist. The resulting moment of force will externally rotate the ski and foot under load out of the turn while simultaneously rotating the leg externally.The graphic below shows the second scenario where the center of pressure W lies directly over the GRF Pivot under the inside edge. In this position, W will load the inside edge under the ball of the foot and assist edge grip. But in this configuration, rotating the ski onto its inside edge necessitates overcoming the moment of force created by the moment arm resulting from the offset between the GRF Pivot and GRF acting at the limits of the sidecut. This requires a source of torque that acts to rotate the ski into the turn about the pivot acting at the inside edge at the waist of the ski.An obvious source of torque is to use the leg to apply force to the inner aspect of the shaft of the foot; aka knee angulation. But this will not create a platform under the body of the outside ski. Applying a load to the vertical wall of the shell opposite the ball of the foot will apply torque load to center at the GRF pivot as shown in the graphic below. The moment arm is formed by the point at which the Turntable Torque is applied to the boot sidewall (green arrow) to the center of rotation at the GRF Pivot.

 

The torque applied to the vertical sidewall of the boot shell is the Effort. The sidecut of the ski is the resistance. What effect will this have on the body of the ski under the foot? There is a lot more to this subject that I will begin to expand on in my next post.

PROBLEMS WITH EXISTING SKI BOOTS

As a segue to my post on Turntable Power and how it cantilevers ground reaction force acting along the running surface of the inside edge of the outside ski, I have decided to post the discussion on the problems with existing ski boots from my US Patent 5,265,350 with associated international patents. The patent was issued on November 30, 1993 (24 years ago) to me as the sole inventor and assigned to MACPOD Enterprises Ltd. (Toronto).

The objective of US Patent 5,265,350 and subsequent patents filed and granted to MACPOD was to identify problems with existing ski boots and offer solutions and a functional criteria for advancing the state-of the art going forward. Some of the problems noted and solutions offered, apply to footwear in general.

The final paragraph raises the issue of the limitations of conventional ski boots in terms of accommodating and enabling biomechanically generated forces such as torque from the mechanical force transfer points of the foot to the structure of the ski boot.

The following material is verbatim from the text of US Patent 5,265,350.


Problems with Existing Ski Boots

Existing footwear (ski boot design) 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. 

Although somewhat vaguely stated, a generally accepted theme has arisen over the years, one of indiscriminate envelopment and “overall restraint” applied to the foot and leg within the footwear. The stated position of various authorities skilled in the art of the design and fabrication of footwear for skiing is that the foot functions best when movement about its articulations is substantially prevented or restricted.

To serve this end, inner ski boot liners are usually formed around inanimate lasts or, alternatively, the foot and leg are inserted into an inner liner within the ski boot shell and foam is introduced into a bladder in the liner so as to totally occupy any free space between the foot and leg and the outer ski boot shell. The outer shell of the footwear is closed around this inner envelopment forming an encasement with which to secure and substantially immobilize the foot and leg. This is considered the optimum and, therefore, ideal form of envelopment. The perspective is that the physiologic structures of the foot are inherently weak and thus, unsuited for skiing. Enveloping the foot within an enclosure which makes it more rigid is thought to add the necessary strength with which to suitably adapt it for skiing. The reasoning being, that the foot and leg now having being suitably strengthened, can form a solid connection with the ski while the leg, now made more rigid, can better serve as a lever with which to apply edging force to the ski.

To some degree, the prior art (existing ski boot design) has acknowledged a need for the ankle joint to articulate in flexion. However, the prior art has not differentiated exactly how articulation of the ankle joint might be separated from the object of generalized and indiscriminate envelopment and thus made possible. Therefore, the theme of prior art (existing ski boot design) is inconsistent and lacks continuity.

The only disclosure known of a process wherein the separation of envelopment of the foot from articulation of the ankle joint is contained in U.S. Pat. No. 4,534,122, of which the present applicant is also the inventor. This material discloses a supportive structure (i.e Dorthotic) wherein restrictions to flexion of the ankle joint are essentially removed, support being provided from below the hinge of the ankle joint.

In keeping with the theme of indiscriminate envelopment and overall restraint, the following structures are generally common to all footwear for skiing disclosed by prior art (existing ski boot design):

(a) a continuous counter system which surrounds the foot and provides for the process of envelopment;

(b) an arrangement of pads or padding with which to envelope the foot;

(c) a substantially rigid outer shell which encases the structures employed for envelopment;

(d) an articulation of the ski boot lower outer shell and the cuff or cuffs which envelope the leg of the user, usually accomplished through a common axis or journal;

(e) a structure to brace and support the leg since prior art considers the ankle joint to be inherently weak and in need of support; and

(f) some form of resistance to movement of the cuff (shaft of the ski boot).

The prior art (existing boot design and boot fitting procedures) refers to the importance of a “neutral sub-talar joint”. The sub-talar joint is a joint with rotational capability which underlies and supports the ankle joint. The sub-talar joint is substantially “neutral” in bipedal function. That is to say that the foot is neither rolled inward or rolled outward.

If the foot can be substantially maintained in a neutral position with the arch supported and with a broad area of the inner aspect of the foot well padded, there will exist a good degree of comfort. Such a state of comfort exists because the foot is not able to roll inward (pronate) to a degree where significant mechanical forces can be set up which would allow it to bear against the inner surface of the boot shell. In effect, this means that initiation of the transition from a state of bipedal to a state of monopedal function, is prevented. This transition would normally be precipitated by an attempt to balance on one foot. If the foot is contained in a neutral position, traditional supportive footbeds (arch supports) are quite compatible with the mechanisms and philosophies of the prior art.

Problems arise when the foot is attempting a transition from a state of bipedal stance to monopedal stance. If the transition to monopedal stance or function can be completed without interference from the structures of the ski boot, all is fine and well. However, if the transition is allowed to proceed to a point where the mechanics associated with the monopedal function can establish significant horizontal forces, and the further movement of the foot is blocked before the transition can be completed, the skier will experience pain and discomfort at the points where the inner aspect of the foot bears against the structures of the footwear. This is the situation experienced by a majority of the skiers with prior art footwear. It is at this point where arch supports, if employed, also begin to cause discomfort. It should be noted that it is the normal tendency of the foot to pronate when weight bearing on one foot.

Footbeds (arch supports) may work in conventional boots (which traditionally do not allow natural biomechanics or movement of the foot to occur), but in a boot which accommodates and supports natural leg and foot articulation and function, arch supports can be detrimental.

When the foot attempts to pronate inside the ski boot, it is often the case that the ankle bone will come to bear against the inner surface of the boot shell. When contact of this nature occurs, pain and other related complications usually result. Since the consensus of those skilled in the art of ski boot design and modification is that pronation or the rolling inward of the foot is detrimental, and, thus, undesirable, provision is not made to allow for such movement. Rather, the structure of the footwear is intended to resist or even prevent it.

Thus, the problem with existing footwear arises due to the dynamic nature of the architecture of the foot. When the wearer is standing with the weight equally distributed between left and right feet so that the centre of mass of the wearer is manifesting itself in the centre between the feet, the architecture of the wearer’s foot assumes a specific configuration. As the wearer begins to shift his weight towards one foot so that the other foot bears proportionately less weight, the wearer’s centre of mass moves over the medial aspect of the weighted foot so as to assume a position of balance. In order for this movement of the wearer’s centre of mass to occur, the architecture of the weighted foot must undergo a progressive re-alignment. Existing footwear does not adequately anticipate this re-alignment of the architecture of the foot and thus such footwear inhibits the wearer’s ability to assume a balanced position.

A further problem with existing footwear is the fact that longitudinal relative movement between the foot and the footwear may occur. This happens, for example, when the forefoot/midfoot section of the foot is not adequately restrained under certain conditions, such as when flexion is occurring between the lower leg and the foot. Such longitudinal relative movement contributes to the disruption of biomechanical reference points associated with the dynamics of the ski and, in addition, results in a delay in the transmission of force between the leg and foot and the footwear.

Yet a further problem with existing footwear for skiing, in particular the rear entry type, relates to the obstruction of the leg in forward flexion. A relatively freely flexing gaiter or cuff (i.e. shaft) is necessary in order to permit the posterior muscle groups of the lower leg to modulate external force exerted on the footwear. This requires that the axis of the footwear be allowed to rotate so that small degrees of flexion/extension occur at the foot with the lower leg being relatively passive and that large degrees of flexion/extension occur as coordinated ankle, knee and hip flexion. The construction of the prior art requires flexion/extension to occur primarily at the knee and hip joints which is disadvantageous to the user.

While some types of rear entry boots do disclose gaiters or cuffs which provide a degree of relatively free flexion, there remains numerous problems, the most serious of which is the fact that the device employed to secure the foot of the user exerts, in addition to the downward directed force on the foot, a simultaneous rearward directed force on the leg which acts to resist forward flexion in spite of any free hinging action of the cuff. The result is an interference with the physiologic function of the foot and leg of the user.

Yet another problem resides in buckle or overlap type footwear. In order to provide for entry of the foot of the user and for resistance to flexion, plastic materials are employed for the outer shell which have flexural qualities. This is necessary in order to facilitate the aforementioned requirements. Plastic materials by their very nature tend to resist point loadings by a relaxation of the material at the point where stress is applied. This characteristic creates serious problems for two reasons. First, the teaching of this application is that force must be applied and maintained only to specific areas of the foot and leg of the user while allowing for unrestricted movement of other areas. The application and maintenance of such force by flexible plastic materials in the structures of prior art is necessarily difficult, if it is possible at all.

Second, the plastic materials in relaxing under the application of stress assume a new shape by moving into void areas. Thus, the probability is great that the plastic material will change shape so as to inhabit the very area required for the uninhibited displacement of the structures of the foot and leg. The result of these limitations is interference with the physiologic function of the user.

Top and rear entry footwear for skiing and skating necessarily have interior volumes greater than that required by the wearers foot and leg, particularly in the area over the instep, in order to accommodate entry. This additional volume makes the incorporation of structures designed to provide accurate and consistent support to specific areas necessarily difficult and ineffective. This results in reduced support for the foot and leg.

Another problem with conventional footwear relates to the flexion of the lower leg relative to the foot. It is desirable to provide a degree of resistance to such movement to assist in dampening movement of the mass of the skier relative to the ski resulting from, for example, a velocity change due to terrain changes and to assist the user in transferring energy to the ski. Adjustment of such resistance is desirable in order that the user may compensate for different physical makeup and different operating conditions. In present ski footwear, sources of resistance for such purpose are poorly controlled and often produce resistance curves inappropriate for the operating environment (i.e. temperature) thereby adversely affecting the balance and control of the user and creating a need for additional energy to be expended to provide correction. In many applications, resistance is achieved by deformation of shell structures thereby resulting in reduced support for the user’s foot and leg. If indeed provision is made for adjustment of flex resistance in the instances cited, it is very limited in terms of ability to suitably modify resistance curves.

Torque Transfer and The Turntable Effect

Yet a further problem relates to the efficient transfer of torque from the lower leg and foot to the footwear. When the leg is rotated inwardly relative to the foot by muscular effort, a torsional load is applied to the foot. Present footwear does not adequately provide support or surfaces on and against which the wearer can transfer biomechanically generated forces such as torque to the footwear. Alternatively, the footwear presents sources of resistance which interfere with the movements necessary to initiate such transfer. It is desirable to provide for appropriate movement and such sources of resistance in order to increase the efficiency of this torque transfer and, in so doing, enhance the turning response of the ski. 

In my next post, I will discuss Turntable Power in conjunction with the Over-Centre mechanism.