Barefoot science posts

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

NABOSO: FEEL THE FORCE

To Dr. Emily Splichal

In recognition of Dr. Emily Splichal’s contribution to my knowledge and through the knowledge gleaned from the use or her pioneering NABOSO surface science technology I am dedicating this post to her as my teacher, mentor and inspiration. Thank you Dr. Splichal.


In this post I am going to discuss how NABOSO surface science technology gave me the feedback mechanism to confirm the optimal ramp angle I needed to transition to a higher level of skier performance.

Optimal Ramp Angles starts with Stance Training

My transition started with refinements to my stance that came from incorporating Dr. Splichal’s principles of foot-to-core sequencing (that connects the feet with the pelvic core) and body fascial tensioning (that unifies the body). Prior to these changes my stance is what I would now define as good but not optimal. The huge improvement resulting from the refinements served as the impetus for a series of posts on the sequencing process required to assume a fascially tensioned stance with foot to core sequencing. I called this the SR Stance. The reason I chose this name was to draw reader attention to the stance posts by making the stance seem innovative, but not intimidating.

KIS is the Stance Kiss of Death

In reviewing material on ski technique, a skier’s stance is described as anything from an athletic stance, a relaxed stance, a ready stance, a balanced stance, a centered stance or a whatever feels good stance. A focus on selling skiing as easy with the KIS principle (Keep It Simple) has resulted in stance being perceived as less than critical to good technique. This leaves most skiers with the impression that a ski stance should feel similar to a relaxed upright stance on two feet with weight equally distributed between both feet and the heels and forefoot of each foot. This is interpreted by skiers as meaning they are balanced or in balance. So it follows that in actual skiing there should be even ‘pressure’ everywhere with no sensation of pressure on any specific area of the foot.

If I ask a typical skier to stand on a ramped surface and assume their ski stance they will find the sweet spot where their weight feels evenly distributed and identify it with their ski stance regardless of the  angle of the surface

So the first challenge to transitioning to a higher level of skier peformance is accepting that a strong ski stance must be learned and consistently rehearsed by doing drills as I do every time I go skiing. It’s like pre-flight check. NABOSO provide the conscious and subconscious CNS feedback that tells me when I am cleared for take off.

The NABOSO Effect

In my post NABOSO PROPRIOCEPTIVE STIMULATION INSOLES, I stated that the principle proprioceptive neural activity associated with balance responses occurs across the plantar plane. It is strongest in the 1st MPJ (big toe joint) and big toe. The fast acting small FA II nerves in this area are activated by pressure and skin stretch both of which occur in the late phase of Mid Stance. Optimal ramp angle is critical because it maximizes both pressure and skin stretch thereby potentiating the sensory input required to initiate controlled movement.

Assuming a NABOSO is trimmed, if necessary, to fit a shoe, there will be a positive effect on plantar proprioceptive stimulation. But my experience to date has been that the plantar proprioceptive stimulation will be much more pronounced in a minimal, zero drop shoe with adequate width for fascial forefoot tensioning and correct alignment of the big toe.

The big breakthrough for me came after I started using NABOSO insoles in shoes with different heel raises (drops). It turned out that I had the highest perception of  pressure under the ball of my foot in late mid stance phase with shoes with zero ramp (drop). When I put NABOSO insoles in my ski boots to test them I could hardly perceive any pressure under the ball of my outside foot during skiing no matter how I adjusted my stance or the tensions in my boot closures. This told me that my ramp angle of almost 3 degrees was far too great. As soon as I reduced the angle to 1.2 degrees (which is what I tested best at on my dynamic ramp angle device) it is no exaggeration to state the the whole world changed. But the transition effect didn’t kick into high gear until this ski season after my brain had time to delete a lot of the bad programming from the old ramp angle.

NABOSO 1.0 on the left. NABOSO 1.5 on the right. I use 1.5 in my ski boots. I purchase the large size and trim to fit.

Tentative Conclusions

  • A system that provides continuous subconscious sensory input to the CNS with the ability to consciously sense sensory input during drills in executive mode is important.
  • Stance training should be incorporated into racer training programs at an early stage and optimal stance ramp angle identified and implemented.
  • Once optimal ramp angle has been implemented the boot should be set up to the skier’s functional specification which I will discuss in future posts.
  • Stance ramp angle should be retested on a periodic basis to confirm the requirements have not changed.
  • Adjustments should be made as soon as possible after the end of a competitive season and no further changes made during the subsequent competitive season.

In my next post I will discuss Dr. Splichal’s protocol for using NABOSO insoles and matts in training.


Disclosure

I am not involved in any form of business association or affiliation or any have business interest or investment with Dr. Splichal/NABOSO/EBFA. Nor do I receive any form of compensation from the sale of NABOSO. Prior to marketing her NABOSO insoles Dr. Splichal provided me with a small sample of NABOSO material at her cost to cut insoles from for testing.

 

 

THE MECHANICS + BIOMECHANICS OF PLATFORM ANGLE – PART 13

The  article that follows was published on June 18, 2010 on an internet group called EPICSKI.  I have revised the article to improve clarity and consistency with the technical terms used in the THE MECHANICS + BIOMECHANICS OF PLATFORM ANGLE series of posts.

The Birdcage Experiments

 by David MacPhail

In the summer of 1991 a science team Steve Podborski and I had assembled to develop a new ski boot conducted pioneering studies on the Blackcomb summer glacier with a device we affectionately named the “Birdcage.” The purpose of the studies was to test my hypothesis of the mechanics and biomechanics of platform angle as it pertains to skier dynamic stability and the basic premise of my hypothesis that explains how  GRF acting on the inside edge of the outski is extended out under the platform of the ski. The Birdcage is shown in the photo below.

Birdcage

The Birdcage was fit with 16 sensors each with its own channel as shown in the legend below.

Specific mechanical points of the foot, in particular the ends of the eccentric torque arm, connected to specific points of the rigid structure of the Birdcage while leaving the remaining areas of the foot substantially unconstrained. The object of the experiments was to study the effects of specific forms of constraint applied to key mechanical points of the foot we had previously identified on skier balance as it pertains to steering and edge control. The experiments also included tests that studied the effect of interfering with specific joint actions. The experiments were designed in accordance with a standard scientific protocol; one that standardized conditions from test to test while varying one factor at a time.

For example, to study the effects of cuff forward lean angle on specific muscles, the range of rotation of the cuff was kept the same from test to test while the initial angle at which the cuff was set was varied from test to test. The cuff was fit tightly about the leg so as to reduce to a minimum any effects of movement of the leg within the cuff. Other aspects of the test such as position of the heel and ball of the foot in relation to the centerline and inside edge of the ski were kept the same.

By using such test protocols the firing sequence of specific muscles and their effect on dynamic stabilty could be studied. This data could then be used to determine the sequence of events and relationship steering to edge platform angle control. It was discovered that by varying the conditions that affected the firing and effectiveness of the soleus muscle, it could be played like a musical instrument. For example, if the cuff angle were set too erect the soleus muscle would make multiple attempts at the start of each loading sequence to try and get COG over the head of the first metatarsal.

Our primary tester for the experiments was Olympic bronze medallist and World Cup Downhill Champion Steve Podborski. Steve is shown in the photos below having the Birdcage adjusted to his foot and leg.

The cable coming from the rear of the device is connected to a Toshiba optical drive computer (remember, this is 1991) that Toshiba loaned us in support of our program. The biomedical engineer and the Toshiba computer are shown in the photo below.

Since telemetry was too costly and less positive we used a 1200 ft cable that linked the Birdcage to the Toshiba computer set up in a tent. Although the technician could not see the skiers being studied within a short period of time he could easily analyze their technical competence in real time by assessing the incoming flow of data from the sensors fit to the Birdcage. This was even more remarkable considering that the technician had no background in skiing, ski teaching or coaching.

The testers wore a harness to keep the cable from interfering with their movements. A chase skier ensured that the cable remained behind the testers and did not pull on the testers. Of interest is the fact that I was unable to elicit any interest in the results of the Birdcage study

As far as I know a study of this nature had never been done before and to the best of my knowledge a similar study has never been repeated since the Birdcage experiments. The Birdcage remains one of the most sophisticated analytical sports devices ever conceived even by todays’ standards. The Birdcage research vehicle is the barefoot minimum standard for the ski boot.

THE MECHANICS + BIOMECHANICS OF PLATFORM ANGLE: PART 6


In my last post I identified whole leg rotation of the head of the femur at its joint in the pelvis as the source of the rotational force acting 180 degrees to the transverse plane of the platform. In the technical terms of skiing whole leg rotational force is called steering.

When I started skiing in 1970 the ability to hold an edge on hard pistes and especially ice was the exclusive domain of elite skiers. Back then, the majority of skiers and racers were still skiing in low cut leather or plastic boots with the shaft not much higher than the ankle bones.

Debates raged in ski magazines as to the reason why elite skiers were able to easily hold an edge on ice while the majority of skiers struggled. The question was posed as to which came first. Did elite skiers edge first and then turn their skis or did they turn their skis and then edge? The consensus was that the best way to hold an edge and not to slip was to establish edge grip early and not slip when the forces increased. Recovering an edge once a ski started to slip was next to impossible. 

Since holding an edge during a turn involves movement of the skier there was no static way to demonstrate how to hold an edge on ice. The only option was watch an elite skier and try and copy them. This was seldom successful because even elite skiers couldn’t describe what they were doing. Strength and athletic ability and/or level of fitness did not seem to be significant factors.  Even elite hockey players often struggled to hold an edge on skis. I had questions but few answers. Finally a female ski instructor gave me a valuable clue when she told me that she presses down hard on the ball of her outside foot to make her edges hold on hard snow.

Clues such as turning the skis and putting pressure on the ball of the outside foot pointed towards the mechanism of the mechanics of platform angle and dynamic balance. But before the mechanics could be explained the introduction of the high shaft rigid plastic ski boot distracted attention away from the problem. High stiff plastic ski boots made it easy for even a novice to stand, crank their knees into the hill and put their skis on edge. This turned out to be a good marketing tool because it made holding an edge appear easy even for a novice. But using the leg as a lever didn’t work except under ideal conditions.

When I tried using my leg to hold a ski on edge on ice I met with marginal success. Later, when I modelled the mechanics the combination of forces didn’t result in a mechanism that would enable a skier to cut a step into hard pistes so as to create a platform and control its angle.

But the crank the knee into the hill option prevailed and took root. It provided an easy way to demonstrate a complex issue. Once knee angulation became established the ski industry appeared to lose interest in trying to discover the real mechanism responsible for platform mechanics. In spite of a protracted effort I didn’t begin to understand the mechanism until about 1989 after getting some valuable clues from the chapter on the ski boot in the medical text, The Shoe In Sport (see my post – THE SHOCKING TRUTH ABOUT POWER STRAPS). But getting insights on the mechanism entailed making some significant discoveries that have only come to be recognized and studied in the l ast 10 years.

One discovery I made that was fundamental to understanding platform mechanics is that the Achilles tendon is capable of transferring large forces to forefoot as the pelvis moves forward in the stance phase of locomotion.

Steer onto the Platform

Although steering and edging are often discussed together they are typically considered different, but related, skills that are blended together. In fact, they are one and the same. Elite skiers steer their skis onto a platform but only if their equipment, in particular their ski boots, enables the requisite neurobiomechanics. 

The Center of Rotation of the Foot 

The turning effort from the pelvis is applied to the foot at the distal (farther end) of the tibia as shown in the graphic below. In terms of position on the running length of a ski this places the center of rotation on the rear half of the ski. The implications are that the forebody of a ski will rotate more across a skier’s line than the tail of the ski. In my foot, the center of rotation is approximately 12 cm behind the running center of the ski.
The femur has a typical range of rotation of 45 degrees in each direction (total ROM 90 degrees); 45 degrees medial (towards the transverse center of the body) and 45 degrees lateral (away from the transverse center of the body). 

If rotational effort is applied to the foot against a firm vertical surface the rear foot will be forced away from the surface.

The implications for skiing are that as the platform angle of a ski with the plane of the snow increases towards perpendicular (normal) to the slope the turning effort applied to the feet will direct the forebody into the surface of the snow. As a reader commented on a previous post on platform angle mechanics the tips (shovel or forebody) of the ski leads the charge. A carved turn starts at the tip with the edges engaging and cutting a step into the snow for the portion of the edge that follow to track in. The shovel leads the charge and starts the carving action. 

Mechanical Points of Force 

A final point for this post is the two key mechanical points where loads on the foot apply high force to the platform; one under the ball of the great toe (i.e. head of the first metatarsal) and the other under the heel in an area called the tuber calcaneum. These are the primary centres of force in skiing. 

The effect of any rotational force or steering to a ski is significantly affected in the carving or loading phase by where the center of force is located. This will be the subject of my next post.

WHY STANCE TRAINING IS ESSENTIAL

When readers click on my blog address at skimoves.me, analytics give me a hierarchy of the countries with the most views and the most popular posts in ascending order. This helps me identify which content resonates most strongly with viewers and which content draws a blank.

As I write this post, the top five countries are the US followed by Croatia, the United Kingdom, Slovakia and France.

The most viewed post today is THE SHOCKING TRUTH ABOUT POWER STRAPS; far and away the most popular post I have published to date. But the most important posts by far that I have ever written, A DEVICE TO DETERMINE OPTIMAL PERSONAL RAMP ANGLE and STANCE MUSCLE TENSIONING SEQUENCE EXERCISE barely sputtered in comparison. This strongly suggests that far from just some small gaps in the knowledge base skiing is founded on, massive craters exist.

Arguably the most important aspect of skiing is a strong stance. Any variance in the fore-aft angle of  the plane of support under the feet and the plane of the base of the ski has significant impact on stance. Yet these subjects are barely blips on the Doppler Radar of the ski industry.

Since I started the dynamic ramp angle assessment project a few weeks ago I have found that when asked to do so, it is rare for a skier of any ability to be able to assume a strong ski stance in an off the ski hill environment. Even when a skier  skis with a relatively strong stance, they seem to lack a sense of what a strong stance feels like. Because of this, they lack the ability to consciously replicate a strong stance. If asked to do so, they would be unable to coach a skier in the sequence of events that I described in my last post

In the dynamic ramp angle assessment project, I  have also observed that skiers with with a boot/binding ramp angle greater than 2.8 degrees appear to have become accustomed to the associated unstable, dysfunctional feeling and identify with it as ‘normal’. Before I can test them, I have to spend time coaching them into the correct stance because it feels unnatural to them.

When I go back and forth between a strong functional stance on a flat, hard level surface to a stance on the dynamic ramp angle device set to an angle of 4 degrees, I can get close to the same angles of ankle, knee and hip. But when I do, I feel strong tension, stiffness and even pain in my mid to lower back which is  common in some skiers and even racers.

Based on results to date with the dynamic ramp angle device, it appears as if strong skiers ski best with ramp angles close to zero. But depending on their sense of balance and athletic ability, they may have a wide range in which they sense little difference on the effect of ramp angle until they approach the upper limit of stability. While they may be able to ski well with a ramp angle close to the maximum limit of stability, ramp angles much above 1.2 to 1.5 degrees may not offer any benefits. This can only be tested on skis where balance is tested by dynamic forces which cannot be replicated in a static setting.

Issues affecting skier stance were discussed in detail in my post, THE SHOCKING TRUTH ABOUT POWER STRAPS. Here are the excerpts I posted from the chapter on The Ski Boot in the book, The Shoe in Sport (1989), published in German in 1987 as Der Schuh Im Sport– ISNB 0-8151-7814-X

“If flexion resistance stays the same over the entire range of flexion of the ski boot, the resulting flexion on the tibia will be decreased. With respect to the safety of the knee, however, this is a very poor solution. The increasing stiffness of the flexion joint of the boot decreases the ability of the ankle to compensate for the load and places the entire load on the knee”. – Biomechanical Considerations of the Ski Boot (Alpine) – Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland

“The shaft of the boot should provide the leg with good support, but not with great resistance for about two thirds of the possible arc, i.e., (14 degrees) 20 to 22 degrees. Up to that point, the normal, physiologic function of the ankle should not be impeded”.

“Previous misconceptions concerning its role in absorbing energy must be replaced by the realization that shaft pressure generates impulses affecting the motion patterns of the upper body, which in turn profoundly affect acceleration and balance.

“When the lateral stability of the shaft (the leg) is properly maintained, the forces acting in the sagittal direction should not be merely passive but should be the result of active muscle participation and tonic muscular tension. If muscular function is inhibited in the ankle area, greater loads will be placed on the knee”. – Kinematics of the Foot in the Ski Boot – Professor  Dr. M. Pfeiffer – Institute for the Athletic Science, University of Salzburg, Salzburg, Austria

It has been over 40 years since international authorities on sports science and safety raised red flags concerning the adverse effects of ski boots design and construction on skier stance, balance and the potential to cause or contribute to injury. It is time that their concerns were taken seriously and acted on. Research on stance and the effect of such things as zeppa and delta ramp angles is urgently needed.

 

ISOMETRIC STANCE MUSCLE TENSIONING SEQUENCE

Tensegrity

Tens(ion) + (Int)egrity 

The optimal ramp angle, as determined by the dynamic ramp device, is based on a stance predicated on the principles of Biotensegrity.

Fascial continuity suggests that the myofascia acts like an adjustable tensegrity around the skeleton – a continuous inward pulling tensional network like the elastics, with the bones acting like the struts in the tensegrity model, pushing out against the restricting ‘rubber bands: Tom Myers, Anatomy Trains (1.)

A ski stance based on the principles of bio-tensegrity must be learned and rehearsed in a step-by-step process. It is neither natural or intuitive although elite skiers and racers such as Shiffrin and Hirscher appear to have acquired the elements of Biotensegrity. Assuming a group of racers of equal athletic ability, the odds will favour those whose stance is based on Biotensegrity.

In a ski stance based on bio-tensegrity, tension in the arches of the feet extends to from the balls of the feet to the palms of the hands holding the poles.

  1. Start by standing barefoot on a hard flat floor or surface in a controlled environment such as your home. Where possible, use the same surface and place to rehearse the stance. If you have constructed a dynamic ramp assessment device, use this with the top plate set to level.
  2. Stand upright at attention. You should feel most of the weight under your  heels and less weight across the balls of your feet. This is normal. The fore-aft weight distribution is actually 50-50 heel to forefoot. But because the weight of the body is spread across the balls of the feet and along the outer aspect behind the small toes, more weight is sensed under the heels. Stand so your weight is distributed equally between both feet.
  3. Relax your hamstrings (in your thighs) and let your torso drop towards the floor.  Your knees will move forward as they flex and your ankles will dorsiflex. Your ankles should stop dorsiflexing on their own when the front of your knee caps are aligned approximately over the balls of your feet. This is the point where the tension in your soleus (calf muscle) peaks with the tension in plantar ligament of your arches. You should feel about the same pressure under the balls of your feet as you feel under your heels. But it should feel as if the circle of pressure under your heels has gotten bigger and your feet are more connected or integrated with the floor. I call this ‘rooted’ because it should feel as if your feet have sunk into the floor.
  4. While keeping your upper body erect, move slightly forward in the hips. You will quickly reach a point where you start to become unstable and feel as if you would fall forward onto your face if you moved farther forward in the hips. When you get to this point your big toes should press down on the floor on their own to try stabilize you. This is the forward limit of stability.
  5. Now move rearward in the hips until you start to feel the same instability. This is the rearmost limit of stability.
  6. Now bend forward from the waist. Do not curl your back. Bend from the hip sockets for the thigh bone (femur). This movement is actually thigh flexion. Lift your thigh to get the right feeling. As you bend forward from the waist, your buttocks will move rearward and upward as your ankles and knees straighten.  Reach forward with your arms as if you were going to hug a large barrel in front of you. Make sure the palms of your hands are facing each other with fingers curled and pointing towards each other.
  7. Find the place where your arms and head feel neutral to your spine. As your arms come into position you should feel your abdominal core and muscles in your back acquire tension. Slings Isometric stance
  8. Experiment by moving forward and rearward in the pelvis. As you move forward in the pelvis the pressure should increase under the balls of your feet. But you should not feel unstable. If anything, you should feel stronger and more stable. You should feel as if the weight of your head and shoulders is pressing your feet down into the floor.
  9. Increase the bend at your waist while keeping the pressure on the balls of your feet and heels until the top of your head is down by your knees. You should still feel very strong and stable in the feet. This is the lowermost limit of waist flexion.

Once you have acquired a kinesthetic sense of the bio-integrity of foot to hand tension, a sense of stability while pulsing the torso vertically up and down over the feet confirms a state of bio-tensegrity.

The photo below is of simple model I designed and constructed in 1993 to illustrate the basic concept of bottom up Biotensegrity and how the degree of passive tension in the plantar ligament of the arches of the feet and the vertical biokinetic chain is driven by the compression from weight of COM stacked over the foot.

The graphic below shows the continuum of tension from the balls of the feet to the opposite shoulders through the mechanism of the oblique posterior sling.

In my next post I will discuss what I term the NABOSO Effect.


  1. https://www.anatomytrains.com/fascia/tensegrity/

FIFTH GENERATION STANCE RAMP ASSESSMENT DEVICE

Since my first version of the stance ramp assessment device I have made a number of significant improvements. The series of photos below are of the fifth generation device.

The bottom plate or base of the device is approximately 18 inches (46 cm) wide by 16 inches (41 cm) deep (front to back). I intend to make the next version about 22 inches (56 cm) wide by 18 inches (46 cm) deep. Size is not critical so long as the top plate is deep and wide enough for the feet being tested.

Stiffness of the plates is critical. Three quarter inch thick (2 cm) plywood or medium density fiberboard (MDF) are suitable materials. I added 1.5 inch x 1.5 inch wood reinforcing ribs on the sides, middle and rear of the top plate.

The photo below shows the heel end of the device. Two 1/4 inch drive ratchets turn bolts threaded into T-nuts in the top plate that raise the heel end up.

The photo below shows the top plate hinged to the bottom plate with 4 robust hinges.

Four telescoping hard nylon feet are set into the bottom plate to enable the device to be leveled and made stable on the supporting surface. It is important that the device not tilt or rock during testing.

The photo below shows the details of the interface between the top plate on the left and the bottom plate on the right.IMG_3409

I used gasket material purchased from an auto supply to shim the forefoot of my boot boards to decrease the ramp angle so as to obtain the 1.2 degree ramp angle I tested best at.Shim pack

The package contains 4 sheets of gasket material that includes 3 mm and 1.5 mm sheet cork and 2 other materials.Gasket

I cut forefoot shims from the 3 mm cork sheet as shown to the right of the boot board in the photo below.BB w shims

I adhered the shims to the boot board with heavy duty 2-sided tape and feathered the edges with a belt sander.shims installed

I corrected the ramp of my boot boards in 3 stages. Once my optimal ramp angle is confirmed, I will pour a boot board into the base of my ski boot shells in place of the existing boot boards using a material such as Smooth-Cast 385 Mineral Filled Casting Resin. More on this in a future post.

Ramp Angle Appears to User Specific

It is important to stress that although there appears to be a trend to optimal boot board ramp angles for elite skiers in the range 1.5 degrees or less, there is no basis to assume a  ramp angle that is optimal for one skier will be optimal for another skier. Recreational skiers are testing best between 2.0 and 2.5 degrees.

It is also not known at this point whether the initial optimal ramp angle identified with the device will change over time. Based on the impressive results seen so far in the limited number of skiers and racers who were tested and ramp angles adjusted there is no basis to assume that ramp angle is not a critical factor affecting skier balance and ski and edge control. Studies on this issue are urgently needed and long overdue.

It is important that testing for optimal ramp angle be preceded by kinesthetic stance training. This will be the subject of my next post.