Ski boot modification posts

A SKIER ASKS QUESTIONS ON BOOT-FITTING 101: THE ESSENTIALS

After my last post BOOT-FITTING 101: THE ESSENTIALS – SHELL FIT, I received an email from a Whistler skier asking a number of questions. I have copied and pasted the questions into the post below and inserted my answers


Whistler Skier: After reading your last two posts and going through all the information about boot fit, the tongue and where your shin should contact the boot/liner, I probably need  to punch the shells a bit wider in the ankle area of the navicular bone (it definitely needs more room when I go from bipedal to monopedal stance).

Answer: Make sure forefoot width is adequate first.


Whistler Skier: 

  • Do you want a full finger width between all parts of the shell and your foot?

Answer: No. Just behind the heel. A few mm clearance to 1st and 5th toe joints and inside ankle bones is usually sufficient if the liner is thin enough in those areas.


Whistler Skier: 

  • Should I just experiment with padding of different thicknesses over my forefoot to try and keep my foot in contact with the bottom of the boot?

Answer: TONGUE CHECK will be the subject of a future BOOT-FITTING 101: THE ESSENTIALS post.


Whistler Skier: 

  • When I put the boot on and lightly buckled, I can still ‘stand on my toes’, so:
    • Is that because my foot is not sitting in the heel pocket?

Answer: I suspect you aren’t standing in an SR Stance. If you were, you would not be able to stand on your toes.


Whistler Skier: 

  • I gather from your postings that I don’t want to add foam to the front ‘crook’ of my ankle to hold it in the heel pocket because it will impede the natural ankle movement on flexion?

Answer: Yes. It might not impede the natural ankle movement. But at the same time, L-pads do nothing useful if the foot is stiffened by fascial tension. It is the age old problem of what is easier to nail to a tree, liquid Jello or frozen Jello?


Whistler Skier: 

  • If so, how do I get my heel to stay in the heel pocket? (do I want it there?)

Answer: Wedge fit loading of the instep of the foot with forefoot portion of the boot tongue. The key is ensuring fascial tensioning can occur in the boot because it makes the foot behave as it were solid, not malleable. Conventional boot fitting strategies attempt to achieve this objective by encasing the foot with a form fitting medium. This has the exact opposite effect. It actually prevents fascial tensioning.


Whistler Skier: 

  • Should I hold off on punching the ankle area?

Answer: For the time being. If it is close, skiing will confirm whether or not the space is adequate.

Whistler Skier: 

  • i.e., Is the space already large enough?

Answer:  I don’t know. See above.

Whistler Skier: 

  • Is it the cuff of the boot that provides control in conjunction with the sole of the foot?  My shin seems to contact the front cuff of the boot right about where your diagrams indicate it should and there is no pressure further down the cuff.

Answer: Sounds good.


The key that has literally been under everyone’s feet for decades, while they threw out nonsensical theories on skier balance, is what I call Ground Control. Given the correct sequencing of events, fascial tensioning in combination with pronation of the outside foot in a turn, enable pelvic rotation of the femur to extend the ground (snow) under the inside edge of the outside ski up under the base of the ski.

The mechanics of Ground Control has the effect of bringing the ground (snow) up under the entire ski base and foot thus allowing a skier to actually balance on the outside ski as if they were standing with their outside foot in full contact with solid ground (snow). This was my hypothesis that the Birdcage experiments confirmed in 1991.

 

BOOT-FITTING 101: THE ESSENTIALS – SHELL FIT

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

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

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

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

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

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

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

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

The above cited study concluded:

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

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

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

The Fascial Tension/SR Stance Connection

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

Immobilize – Support – Stabilize

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

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

Fascial Tensioning and the Human Foot Lever

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

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

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

The DIN Standard is Not a Foot Standard

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

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

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

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

The Importance of Foot Splay

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

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

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

mt-width

Shell Check: Start Point 

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

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

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

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


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

FEATURE POST – ASSESSING CHANGES TO SKI BOOTS

Since the summer and fall is a time when racers and serious skiers make changes to ski boots, I will describe the strategy I use to assess changes. It is important to make changes in a manner that controls variables and provides a baseline to make one-on-one comparisons against. However, after viewing video provided to me by several followers of my blog that graphically shows the effect on technique of changes made to ski boots over a number of years, it became apparent to me that few, if any, racers or elite skiers have any idea of what a ski boot should ideally feel like and especially how it should affect them in terms of performance.

Without clearly defined end objectives and a sequential process for achieving and confirming successful implementation, skiers and racers can only think in relative terms of better or worse, not optimal.

ASSESSING CHANGES TO SKI BOOTS was originally published on July 11, 2015. The entire post can be viewed at  http://wp.me/p3vZhu-15C

It should be read in conjunction with BOOT-FITTING 101: THE ESSENTIALS – BOOT BOARDS

 

BOOT-FITTING 101: THE ESSENTIALS – BOOT BOARDS

Those who went through the 9 exercises in TRANSITIONING THE SR STANCE TO THE SKI BOOT  probably ended up with a number of red flags. Starting with this post, I will go through what I consider to be the essentials of boot-fitting.

While I use the term boot-fitting, I prefer the term boot-modification. Boot-fitting and fit of a ski boot imply a fit of the boot with the foot and leg that results in a degree of dysfunction of the foot. The key to skiing with minimal effort and maximum balance and comfort is a ski boot that creates a functional environment for the foot and leg as opposed to a ski boot that creates an environment that results in a significant degree of dysfunction of the foot and the entire lower limb.

Achieving a functional environment in a ski boot for the foot and leg is about sequence. The fastest route to a ski boot that provides the best functional environment for the foot and leg is a step-by-step process; one that assesses the effect of each essential component in a systematic manner. A minimalist approach makes it easy to assess the effect of changes such as substituting a custom footbed that supports the arch for a baseline flat insole. The gold standard in studies to assess the effect of interventions such as insoles and orthotics is to compare barefoot balance on one limb to balance on the same limb in a specific form of footwear to balance on the same limb in the same form of footwear fit with an insole or orthotic. This protocol enables the effect of a compounding series of interventions to be assessed against a consistent baseline; in this case, barefoot balance on one limb.

Where I Start

At the bottom. By at the bottom, I mean the boot board (aka, the Zeppa).

I prefer to start with a monoplanar boot board. Monoplanar means flat in both the long and transverse axes of the boot board with the plane of the transverse axis parallel to the base plane of the sole of the boot.

Why monoplanar? Because the shape of the boot board can significantly affect foot function and the fact that the shapes of boot boards and materials and construction can and do vary considerably from one boot brand to another and sometimes even among different models in the same brand. The shape of a boot board can also act to compound the shape of custom footbeds and orthotics. A monoplanar boot board establishes a baseline with which to assess the effects of foot function irrespective of the boot brand or model. A monoplanar boot board and a flat insole serve as a baseline reference with which to assess the effect of any changes to that alter the monoplanar surface form of the boot board.

In my opinion, boot boards are one of the weakest components of a ski boot. Boot boards are one of the first things I check when I am considering purchasing or working on new ski boot. In future post, I will discuss a recent study that raised significant issues with boot boards.

What I Look For

Ramp or Zeppa angle is important. But before I even consider this aspect, I check the construction and materials of the boot board. Although I have not conducted an extensive review of boot boards, I consider both the boot boards and the insoles (after heating and pressing them flat) in Head Raptors some of the best I have seen to date.

The photo below shows a boot board from an Atomic boot (upper 2 photos). A boot board from a Head Raptor is shown in the bottom photo.

1

The 2 photos below are of side and top views of a boot board from a Head Raptor SD. One thing I deem important is continuity across the heads of the metatarsals, especially the head of the first metatarsal (ball of the foot). With the boot board in place, no break in surface continuity should exist between the interface of the boot board and the surface of the boot shell. It is especially important that there is no step at the interface where in the boot board or shell base are at different elevations.

img_5550img_5548

The photo below shows a boot board from a Salomon SX 90 rear entry boot. This type of boot board construction is still found in some recreation boots. I would not consider a ski boot with this type of boot board.

4

The main reason I prefer boot boards like the one shown in the photo below is that it is fabricated from dense hard foam. Any contour can be quickly and easily removed with a sharp block hand plane. Ramp angle can also be easily and quickly adjusted with a sharp block plane. I use a belt sander to finish the surface

plane-bb

When the front portion of a board needs to be raised to correct zeppa angle, I use a material like dense gasket cork. The photo below shows boot board from a Head recreational boot with a layer of cork added to the front half to reduce ramp angle.

img_6627

With the boot board in place in the shells, the insoles from the liners should be placed on top of the boot boards in order to ensure that the foot is sitting at the correct elevation in relation to the shell walls when checking for clearances.  The insoles shown in the photo below are from a Head Raptor.

head-insoles

In terms of resiliency and surface texture, the Head insoles in the above photo are some of the best insoles I have found to date. I heat and press them flat in order to create a baseline insole.

Once a skier or racer has adapted to the baseline fit of a ski boot they can replace a baseline insole in one boot with a custom insole or orthotic and compare it to the  baseline insole in the other boot. If the boot is perceived to be better with the custom insole or orthotic, the baseline insole in the other boot can be swapped. If there is any doubt after a ski-in period, the process is easily reversed.

The protocol I follow is to make one change at a time and always ensure is quickly and easily reversible.

My next post will be on BOOT-FITTING 101: THE ESSENTIALS – FOOT TO SHELL CLEARANCES

UPDATE ON THE FREEMOTION SKI BOOT PROJECT

On December 9, 2016,  Simon Zachhuber from Austria posted the following comment on my blog.

Dear David! While researching for a university-project (FH-Salzburg, Austria) I discovered your blog! Clearly you are an expert on ski boots, and I thought maybe you can provide some feedback! At least it’s worth a try

I’m a product designer and our task is to analyze a specific ski boot and try to figure out ways to improve it! The ski boot we work on has a new concept of dealing with the occuring forces. Instead of providing stability and flex with plastic shells, the forces are applied to a metal spring. So the area of the tong and the shin doesn’t have to be covered with hard plastic, but with leather or fabric. You can see the concept on their website http://www.freemotion.cc

I am currently working on a project as a student for the FH Salzburg, Austria! We have the task of analyzing a specific ski boot and implementing improvements! Since this is a short project and we are not experts on ski boots, I wanted to ask you for profound feedback on this boot! It can be seen on the website http://www.freemotion.cc

The boot’s concept is that instead of having a hardplastic-shell to deal with the forces, it uses a metal spring that starts at the forefoot and goes through the ankle-axis all the way back over the heel! We already tested it and were quite surprised, how well it worked, but maybe you can add a few thoughts that come to your mind when you check the boot?
I know, it’s very hard to give feedback without having the boot to test, but maybe you can still give some feedback? Thank you very much!!!

With greetings from Austria
Simon Zachhuber


I replied to Simon by email

Dear Simon,

Greetings from Whistler, BC Canada.
I would be glad to assist you in any way I can with your project.

Do you know of the work of Dr. Martin Pfeiffer of the University of Salzburg? He was committed to the development of a ski boot designed along anatomical principles. Two Canadian radiologists of Austrian descent made me aware of Dr. Pfeiffer’s work in 1988 when they gave me a copy of Der Schu Im Sport. Part 6, The Ski Boot, features a chapter by Dr. Pfeiffer called Kinematics of the Foot in the Ski Boot. Dr. Martin Pfeiffer was a source of valuable knowledge that influenced my work. I had personal communication with him in the early ‘90s.

Dr Pfeiffer concluded his chapter by stating, “This goal (a ski boot designed along anatomical principles) has not yet been achieved”. I do not know whether he is still with us. But I would appreciate you recognizing his contribution to skiing by making his vision a reality and by recognizing his work.

Best regards,
David


Due to the urgency of Simon’s deadline (which was fortunately later extended to January 17, 2017), I made providing my assistance a priority with the following series of posts.

NEW AUSTRIAN SKI BOOT: THE FREEMOTION – http://wp.me/p3vZhu-1CB

SIMON RESPONDS TO MY PRELIMINARY OBSERVATIONS ON THE FREEMOTION SKI BOOT – http://wp.me/p3vZhu-1D9

POTENTIAL SOLUTIONS FOR THE FREEMOTION SKI BOOT – http://wp.me/p3vZhu-1Dt

THE FREEMOTION SKI BOOT:  FLEXURAL BEHAVIOUR – http://wp.me/p3vZhu-1FB

FREEMOTION FLEX CURVE OPTIONS – PART 1 – http://wp.me/p3vZhu-1Gj

FREEMOTION FLEX CURVE OPTIONS – PART 2 – http://wp.me/p3vZhu-1Gy

FREEMOTION FLEX CURVE OPTIONS – PART 3 – http://wp.me/p3vZhu-1GI


On January 18, 2017, the following video was posted on YouTube on the FreeMotion site with the text below translated from German.

Kooperation Freemotion mit der FH Kuchl

The results of our successful cooperation with FH Kuchl are here! We are delighted about the great input of the students and professors. We are already working on the implementation of the ideas. Once again a big thank you to the students #Feelgoodskiboot

 


I sincerely hope that my efforts have assisted the students of FH Kuchl. The design of the ski boot needs fresh young thinking and a new direction with design based on the functional requirements of the human system. The most satisfying aspect of the design exercise at FH Kuchl was to see the large female component with students Marlene Arabjan and Evelyn Obermuller taking an active role.

Gut gemacht Simon  Zachhuber und die anderen studenten von FH Kuchl!

Viel Gluck und Best Wunsche

FREEMOTION FLEX CURVE OPTIONS – PART 3

A plausible reason why the FreeMotion boot has failed to gain acceptance is that the spring flex concept has not been tested in a medium that allows all the critical variables discussed in my last post to be adjusted to the individual skier. An essential prerequisite to this process is a validated physiological model; one that explains the physiologic processes of skier balance as well as the mechanics and biomechanics associated with the 3-dimensional physical environment of the activity.

While the Birdcage allowed adjustments specific to individual skier requirements to be made and data to be acquired that showed the effects on skier performance, in particular, skier balance, insufficient time and budgetary constraints limited the study of flex curve requirements.

Figures 52 and 55 A through D below show the flex assembly for the Birdcage. The details are disclosed in the section of the patent associated with aforementioned figures.

fig-52fig-55

Figure 56 below shows the different components of the Birdcage shaft adjustment and flex system resistance curve. The details are disclosed in the section of the patent associated with Figure 56.

fig-56

The photo below shows the actual flex system on the rear of the Birdcage. The nut under the rear stop lug allows for adjustment of the forward lean angle of the shaft. In this photo, the shaft is in the rearmost (hard stop) position with the lug seated against the rear stop nut on the spine.

img_1664

The photo below shows the gap between the lug and the washer-cyclinder assembly that presses on the coil spring after a pre-set number of degrees of forward flexion.

Experiments were done with several types of coil springs, including compound coil springs where a small coil spring is nested inside a larger spring. The rubber donut at the top of the assembly prevents the ‘brick wall’ deceleration effect that occurs when the coil spring is fully compressed. Different types and assemblies of rubber donuts were tried in conjunction with different coil spring configurations.

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In the photo below, the shaft of the Birdcage has rotated forward through the constant low resistance travel segment and is about to compress the coil spring assembly. This position is associated with isometric contraction of the triceps surace (calf muscles) in the SR Stance.

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The photo below shows the coil spring in the initial stages of compression.

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The effect of flexural qualities of the shaft of a ski boot on skier function and balance require structured studies conducted with instrumentation and data acquisition. Fortunately, papers on such studies have recently been published. I will discuss them in my next post.

FREEMOTION FLEX CURVE OPTIONS – PART 1

For those who are new to the Skier’s Manifesto, welcome.

I became involved in an effort to design a new ski boot at the request of Crazy Canuck, Steve Podborski. Steve was (and I think still is) the only non-European to win the World Cup Downhill title. Steve also won a bronze medal at the 1980 Lake Placid Olympics. After he won the World Cup Downhill title he asked me if I could design a boot that would do for every skier what the boots I had built from components that used a new fit technology I had invented did for him. I saw this as an opportunity to advance skiing. I accepted.

I did not take on this project to make money. I took it on because I saw problems with equipment, especially ski boots, that were significantly affecting the enjoyment of the sport for the majority of skiers. I wanted to try and solve these problems and contribute to the betterment of a great sport.

In 1978, I started down the road to try and improve the ski boot by working with world class racers such as Steve Podborski. Today, my focus and mission remains unchanged. I am still working with skiers and racers and I am still learning. When Simon Zucchuber asked for my assistance with the Freemotion ski boot project, I did not hesitate to offer my assistance.

You can learn more about me under the HOME heading on the opening page.


Over the past week, I spent time going through my US Patent 5,265,350 trying to recall the events that influenced my thinking.

The first patent awarded to me was US 4,534,122. It was filed on Dec 1, 1983 and issued by the US Patent Office on August 13, 1985. The patent is for an innovative in-boot fit system that constrains the forefoot without obstructing the glide path of the ankle joint.

When I invented the fit system disclosed in the patent, I knew I was headed in the right direction. But I also knew that I did not have a full understanding, let alone a solution, for the flexural aspect of the ski boot. Between 1973 and 1983 I had come to understand that boot flex was affected by material stiffness, temperature and closure tension. But two of the biggest issues were that buckle boots flexed by deformation of what is a U-shaped tube (which made flex unpredictable) and the angle of the rear cuff that had minimal or no adjustment. This meant that the angle of the shank of a skier was determined by the mass of the calf muscle at the top of the shaft. Attempts by others to address flex had typically focussed on one issue at the expense of another or even caused new problems.

Devising a system for boot flex that would solve all issues and especially one that did not rely on shell deformation led me to the exo-skeleton format around 1987. A patent for this format was not filed until April 25, 1989 because of the time it took to work with lawyers and try and figure out how to define and describe the technology so it would meet the novel requirement for a patent.

Figure 1 below is from the initial patent filing for the patent that was eventually issued on November 30, 1993 as US 5,265,350. This figure and the material in the application established a priority date for the length of the eventual patent. This initial patent was later abandoned in favour of newer iterations.  All of the ‘improvements’ are described in the patent which can found by searching the patent number US 5,265,350 in the US Patent or Google Patent web sites.

 

fig-1

The device is a exo-skeleton arrangement with a tube for the leg attached to the base by arms on each side that rotate about an axis (23) on the base structure (11). A single wide band secures the front portion of the tube (shaft) about the leg of a user to the rear portion.

A bendable spring (40) is affixed to the base on the outside (lateral aspect) of the base (11). An adjustment (42) allows the spring to be moved closer or further away from the two contact arms (43 and 46). The contact arms slide up and down in a channel on the arms so as to allow for an amount of low consistent low resistance cuff rotation before higher resistance is introduced or allow spring resistance to be introduced earlier.  Contact arm (46) can be adjusted up or down the arm so as to change the resistance curve.

An adjustment means (generally shown at 30) allows the angle of the cuff to be adjusted. This enables a user to obtain the correct forward lean angle for the shank which I knew by then was critical (see the posts on SR Stance).

Figure 1 is a rough or what is called a schematic concept of the exo-skeleton system. The next step was to try and come up with a design with aesthetic qualities. Figure 5, below, shows the exo-skeleton of Figure 1 with a soft liner. The attachment for flex spring has been incorporated into the axis journals for the arms of the exo-skeleton.

fig-5

About 1989, I was approached by a husband and wife radiology team. They taught radiology at a university. They were both keen skiers. They heard about my project to develop a ski boot based on anatomical principles and offered their assistance. They presented me with a copy of a recently published book called The Shoe in Sport – Supported by the Orthopedic/Traumatologic Society for Sports Medicine (OTS).  The Shoe in Sport was initially been published in Germany in 1987 as Der Schu Im Sport. They were of German background. That was how they knew about the book.

I found the knowledge contained in The Shoe in Sport invaluable, especially the article the ‘Kinematics of  the Foot in the Ski Boot’ by Professor Dr, M. Pfeiffer of the Institute for Athletic Sciences at the University of Salzburg, Salzburg, Austria. The information contained in The Shoe in Sport helped crystallize many of the issues I had been struggling with and profoundly influenced the thinking behind the Birdcage and the Birdcage experients conducted in the July of 1991 on Whistler Mountain’s glacier.

For the first time, I felt I was on solid ground with my thinking. I was ready to go boldly forward and break new ground.

… to be continued in Part 2.