ski equipment

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.

 

 

 

 

EDGE CHANGE INERTIA + ROCKER ROTATION INERTIA

As I was in the process of writing this post, a FaceBook group on skiing posted a link to an article From PSIA: Examining Transitions. The article is based on a presentation last fall by US Ski Team Head Men’s Coach, Sasha Rearick, in which he shed new light on transitions (1.).  While Rearick did shed light on some events associated with transitions, as with previous efforts by others on this subject, Rearick failed to shed light on the mechanics and physics associated with edge change.

As I explained in my last post, transferring the weight from the outside foot and ski of a turn to the inside foot and ski in the transition phase sets in motion what I call the Eversion/Internal Rotation Cascade that rotates the base of the ski into a transient moment of full contact with the surface of the snow between changing to the new (downhill) edge.

At the start of the transition leading up to ski flat between edge change, the center of pressure (COP) of the weight of the body applied by the sole of the inside foot will be under the heel where it is aligned on the proximate center of the ski. In this configuration, the force applied to the ski by the skier is working with gravity to rotate the ski.

The post left off by showing how rotational inertia will tend to make the ski continue rotating about the uphill edge past ski flat and penetrate into the snow surface on its downhill aspect as shown in the graphic below.

Rotational inertia will tend to make the inside edge of the new outside ski automatically rotate into the turn except for the fact that the force FW applied by the skier is on the wrong side of the new edge.

The graphic below has a dashed red reference that is parallel with the snow surface.

If the force FW applied by the skier is still aligned on the transverse center of the ski, it act will act to oppose edge change as shown in the graphic below. When the axis of rotation of the body of the ski changes with a change in edges, the transverse aspect of the base of the ski and the platform under the skier’s foot will tend to accelerate into an eversion translation. But this can only happen if the associated biomechanics are not interfered with by the structures of the ski boot.

The graphic below shows the change in the mechanics of rotation associated with edge change.

At the start of the transition, movement of the mass of the skier’s upper body is in phase with the downhill rotation of the ski and the force FW applied to it. But when the ski changes pivots at edge change and the mass of the skier continues to move downhill, the force FW applied to the ski will tend to rotate it back to ski flat; i.e out of the turn, unless the point of application of force FW changes during ski flat as shown in the graphic below and COM of the skier is aligned with force FW.

………. the angle between the platform and force you apply to it, the platform angle, must be 90 degrees or smaller.  – page 19, The Ski’s Platform Angle, Ultimate skiing; Le Master

The shift in center of pressure from the heel to the ball of the foot in a turn sequence seen in pressure studies of expert skiers is well documented (2., 3., 4). What the studies are really confirming is the use by expert skiers of the Two Phase Second Rocker mechanism to rock (tip) the outside ski on edge and control the edge angle during the load phase of a turn sequence.

Since the limit of the position of the application of force by the foot in relation to the inside edge of the outside ski is the center of the ball of the foot the effect of ski width underfoot and stand height should be obvious. Both rotational inertia and torque will increase as the width of a ski underfoot (profile width) is reduced and stand height increased. When Ligey says he creates pressure, he is creating far more than just pressure.

While LeMaster appears to recognize the importance of a platform angle less than 90° for edge control and, to some degree, the effect of stand height, the explanation offered for superior edging is that this can be attributed to waist width and stand height making skis more like ice skates.In my next post, I will discuss the role of Turntable Rotation in setting up a platform under the body of the outside ski for a skier to stand and balance on while maintaining edge angle.


  1. http://eliteskiing.com/2017/03/31/from-psia-examining-transitions/
  2. WHAT THE TWO HIGH PRESSURE COPS IN THE UNIVERSITY OF OTTAWA STUDIES MEAN – https://wp.me/p3vZhu-1fV
  3. IMPLICATIONS OF THE UNIVERSITY OF OTTAWA PRESSURE STUDIES –https://wp.me/p3vZhu-1e2
  4. AN INDEPENDENT STUDY IN SUPPORT OF THE UNIVERSITY OF OTTAWA FINDINGS – https://wp.me/p3vZhu-1gR

 

WHY YOUNG TALENTED SKI RACERS FAIL AND EVENTUALLY QUIT RACING

The impetus for the subject of this post came from interest in my post FEATURE POST: MIKAELA SHIFFRIN: THE POWER OF SHEAR FORCE and an article (1.) in the  February 14, 2017 edition of Ski Racing by sports psychologist, Dr. Jim Taylor.

Taylor’s article, aimed at U14 and younger ski racers, points out that this is the age where the foundations are laid which often determine how well a racer does and especially how long they will remain in ski racing. Taylor cites statistics that show that qualifying for Topolino or the Whistler Cup (international competitions for 13-15 year olds) isn’t highly predictive of success even five years later. Specifically, only 25% of those who qualified for those race series later earned a spot on the USST. Moreover, 35% were off the elite ski racing radar within four years; some before their 18th birthday. The problem, that is the focus of Taylor’s article, is that parents enter what he calls the “too” zone, where the parents of kids, who are 11 years old or younger, have become “too” important to the parents who have become “too” invested in how their kids do (or don’t do).

The question I have is what events preceded parents getting to the “too” zone? I have seen more than one situation where a child who started ski racing at a very young age and who was considered to be a child ski racing prodigy, had a promising racing career unravel soon after reaching their teens. Why? What, changes happened that could have caused such a tectonic shift?

Let’s go back to beginning when a racer first showed promise. Many racers demonstrate prowess when they are only 4 or 5 years old. Often, one or both parents are elite skiers and one or both may have raced. In such a situation a young racer would have had an excellent role model that would have helped them  become comfortable by following one or both of their parents down the ski hill. But there are also other important factors in a young racer’s favour:

  • They are usually light weight.
  • They are usually short in stature.
  • Their muscles and skeleton are not yet fully developed.
  • Their feet are usually small.
  • They may lack fear.

A significant factor is that young racers often learn to ski in their mother’s ski boots or boots that would be considered too big for their feet if they were older. The implications? Young racers acquire a kinesthetic sense of how to stand in their boots in what I call the SR (stretch relfex) Stance (3. to 10.). As a consequence, they acquire dynamic stability that provides superior edge and ski control while enabling the myotatic stretch reflex balance response.

The authors of a Polish study on skier balance (2.) cite three types of postural reactions to external forces that disturb equilibrium and can cause the body to lose balance can be observed.

  1. The first reaction is the myotatic stretch reflex, which appears in response to changes in the position of the ankle joints, and is recorded in the triceps surae muscles. This is the earliest mechanism, which increases the activity of the muscles surrounding a joint that is subject to destabilization. Spinal  reflex triggered by the myotatic stretch reflex response causes the muscle to contract resulting in the stiffening of the surrounding joints as a response to the stimulus that has disturbed the balance. For example, changes in the angle of the joints of the lower limbs are followed by a reflexive (fascial) tensioning of adjacent muscles. The subsequent release of the reaction prevents excessive mobility of the joints and stabilises the posture once again.
  2. The next reflex in the process of balancing is the balance-correcting response, which is evoked in response to a strongly destabilising stimulus. This reactive response has a multi-muscle range, and occurs almost simultaneously in the muscles of the lower limbs, torso and neck, while the mechanisms that initiate the reaction are centrally coordinated.
  3. The last of the three types of muscular reaction is the balance-stabilising response. In a situation of a sudden loss of balance, a myotatic stretch reflex first occurs and is then is followed by a balance correcting response, which prevents or attempts to prevent a fall.

I call these balance responses green (postural reaction 1), orange (postural reaction 2) and red (postural reaction 3).

As young racers enter their teens, a number of significant changes have occurred.

  1. They are much heavier.
  2. They have grown in height
  3. Their muscles and skeleton are more developed.
  4. Their feet have grown larger and are more defined.

It is about this time in what is appearing to be a child’s promising racing career, that parents turn to the experts in a well intended effort to maximize their child’s chances of success. One of the key things parents often do is to get race boots for their child and have them customized with footbeds, form-fit liners and increasingly, heat molded shells. The process typically involves what is called race fit wherein ski boots are downsized to the smallest possible shell that the feet can be squeezed into. Custom footbeds or orthotics are considered an essential integral component of race fit because they prevent the foot from spreading and elongating. But this actually interferes with or even prevents the fascial tensioning process that enables dynamic stability and the myotatic reflex associated with the ultra high speed spinal reflex balance response (11).

No longer able to use the myotatic reflex (Green = Normal) balance response, the CNS shifts to Level 2 (Orange = Caution) or even Level 3 (Red = DANGER).

What happens next? The young racer starts to become intimidated by courses and conditions they were previously comfortable with. When this happens, their brain senses imminent danger of serious injury or worse and resorts to what I call the Survival Technique. Survival becomes the priority of the CNS at the expense of speed. Racers start losing ground to lesser racers. Not understanding the cause, parents and coaches can start pushing the child in an effort to get results. The more the child tries, the worse things get. When this happens, frustration sets in. Eventually, the child no longer wants to race. Defeated by their boots, the child eventually quits ski racing and takes up some other sport.

Unfortunately, this story is all “too” common. This is also one of the “toos”.


  1. What Young Ski Racers Need – http://www.drjimtaylor.com/4.0/young-ski-racers-need-dont-need/
  2. Influence of a nine-day alpine ski training programme on the postural stability of people with different levels of skills  (April 2016, Biomedical Human Kinetics (DOI: 10.1515/bhk-2016-0004) – Michał Staniszewski, Przemysław Zybko and  Ida Wiszomirska,  Józef Piłsudski University, Warsaw, Poland.
  3. THE SR STANCE: SURFACE EFFECTS,
  4. THE SR STANCE AND TOTAL BODY CORE INTEGRATION
  5. SR STANCE: ROUNDING THE BACK AND SHOULDERS
  6. THE SR STANCE: AFFECT OF JOINT ANGLES ON COM
  7. LEARN THE SR STANCE IN 3 EASY STEPS
  8. SR: ACHILLES-ARCH TENSION
  9. SR STANCE BASICS: ECCENTRIC MUSCLE POWER AND THE STRETCH REFLEX
  10. I-C-E: SR
  11. INNATE FLOW BALANCE

BOOT BOARD (ZEPPA) RAMP ANGLE VS. BOOT SIZE

It is becoming clear, the angle the boot board (zeppa) establishes for the skier’s foot relative to the ground, is vitally important to the ability to balance and function on skis. Therefore, knowing boot board angle (ramp angle) and skier preferences should become part of every boot setup and purchase. Yet there appears to be a fundamental error in the understanding of ramp angle in boots. This is evident when someone states, for example: “The head Raptor has a ramp angle of 4.5 degrees”. The statement may only true if the angle is linked to the boot size.

There are production controls applied to boots just as controls and standards are applied to all other things mass produced. In boots, it means the first prototypes are designed to a specific size (generally Mondo 26). All other sizes are scaled up or down from it. Each Mondo size is a change of one centimeter. Zeppas are fixed in both rear foot and forefoot height in the prototype standard. Only the zeppa length changes as boot size changes.

It means; if the prototype size is twenty six, the zeppa of a twenty three is three centimeters shorter with the same toe and heel heights. Therefore, the ramp angle of the zeppa of a twenty three is steeper than the ramp angle of the zeppa of a twenty six. Since many women’s boots are scaled from the twenty-six Mondo standard, boot set-up problems can be more difficult to solve for women than for men. This is the reason women are more adversely affected by boot configuration than men. The graphic below compares the boot board (zeppa) ramp angles of larger and smaller boots to the standard Mondo 26 boot.

Zeppas Mondo 26

 

Bindings obviously confer the same effect, since with most models heel height is greater than toe height. As the heel and toe change distances from each other according to boot size, binding angle (delta) changes and its angle is additive with the boot ramp angle to determine gross equipment angle as shown in the graphic below. Binding delta has a double effect, since as delta increases boot cuff angle relative the ground also increases.

Zeppas Mondo 26 bindings

When talking about boot boad ramp, we should include the boot size or always use the ramp of the Mondo 26 as a known reference.


Lou Rosenfeld has an MSc. in Mechanical Engineering with Specialization in Biomechanics earned at the University of Calgary Human Performance Laboratory. His research was titled, “Are Foot Orthotic Caused Gait Changes Permanent”.

While at HPL, he assisted with research on the effects of binding position for Atomic, and later conducted research for Nordica that compared Campbell Balancer established binding position to the Nordica factory recommended binding position.

Lou is one of the invited boot-fitters on the EpicSki forum “Ask the Boot Guys” and has authored articles on boot fit, balance, alignment and binding position for Ski Canada, Ski Press, Super G, Calgary Herald, and Ski Racing, USA. He is a CSIA Level 2 instructor and CSCF Level 1 coach. He currently resides in Calgary where he owns and operates Lou’s Performance Centre. A selection of his articles may be found at www.Lous.ca.

MORGANS’ EXPERIMENTS WITH BOOT SETUP: 2013 TO APRIL 2015

When Morgan Petitniot, from Font Romeu Ski Resort in Southern France, sent me a video titled ‘Ski Gear Comparison – David MacPhail‘, in which he documented his experiments with different ski boot setups, I was both suitably impressed and flattered. Morgan came across as an athletic individual; one who took skiing very seriously. He was determined not to let anything stop him from reaching the highest possible technical level. And yet, his ski equipment had been doing precisely that. In viewing Morgan’s video, I was both moved and impressed by his dedication and logical approach. Even more impressive is that Morgan realized his equipment was adversely affecting his skiing and impeding his progress. In many ways it was a deja vu experience for me; one that reflected my own journey.

Here are a series of screen shots of title scenes from each of Morgan’s experiments between 2013 and April of 2015.

TITLE

(Click on images to zoom in)

Morgan, “For the first time in 2013 I saw me skiing (on video). It was the worst day of my skier’s Life ! I saw me totally blocked, tall, with little flexion at the ankle, knee and hips.”

Jan 2013

Morgan, “So I applied what I was understanding on skier’s manifesto.”

Dec 2014 copy

 

Feb 2015

 

Mar 16

 

Mar 28

 

Mar 2015
April 10

 

April 17 soma

 

April 17

FINALLY SUCCESS!

April 17 Lange tongue

In my next post I will analyze Morgan’s skiing in his video and describe the events and sequences I look for that indicate problems caused by the ski boot

 

THE EVOLUTION OF SKI EQUIPMENT AND ITS INFLUENCE ON SKI TECHNIQUE

If you are like most, you probably assume that the design of ski equipment, especially ski boots, is based on sound principles of science, and that products are thoroughly tested for their effect on the user. After all, attaching a ski to the foot dramatically alters its shape and form and especially the nature of any external forces applied to it.  So it would seem both logical and reasonable that products that have the potential to significantly alter the function of the foot and lower limb would be thoroughly evaluated and tested. But if you thought they were, you would be wrong. A recent paper, Materials, Designs and Standards Used in Ski-Boots for Alpine Skiing (October 21, 2013) states, “Despite the large market of ski equipment, not many scientific papers have been published on this subject in the past.” – Sports 2013, 1, 78-113; doi:10.3390/sports1040078. So how is equipment tested? According to the paper, “The development of alpine ski equipment has been done, in the beginning, mainly by trial and error, using on-snow tests.” Although materials and methods used in the design and manufacture of ski equipment have significantly advanced in recent years, the testing of new boots and skis appears to have remained largely subjective. A company comes out with a new boot or ski format or an accessory like Jet Stix and industry skiers try to come up with the best way to use it through on-snow testing. When shape skis were introduced, the pure carved turn was promoted as the new way to ski. In the order of things, the product comes first, learning how to use it follows. The latest innovation of equipment makers seems to be accepted and embraced without question.

In reviewing the history of ski boots over several decades, every possible format has been tried; low cut leather boots, low cut plastic boots, high cut plastic boots, knee high boots, lever boots, soft boots, top entry, side entry, rear entry, you name it, it has been tried (https://en.wikipedia.org/wiki/Ski_boot). Was any consideration ever given as to the effect these formats had on the end user or whether they made skiing unnecessarily difficult? As far as I can tell, the answer is no. The ski industry model appears to be based on the industrial mass production model wherein the end objective is ‘the least product for the most money’. In this model, ski equipment, ski teaching methodologies and, to a lesser extent, race coaching, are predicated on paint-by-number processes and averages, not individual skier needs.

My early attempts to improve the fit (reduce the looseness) of my own ski boots were limited to the established practice of adding foam or felt pads to liners adjacent the ankle bones and around the heel to tighten the fit. Fitting was a very general concept that mostly involved adding padding to liners, not removing it. When foamed-in-place and thermoformable liners were introduced, the narrative became focussed on the perfect fit of the ski boot with every nuance of the foot and leg. It was in the spring of 1978 that I first became aware of claims emerging within the ranks of the ski industry that the foot functions best in skiing when its joints are immobilized in neutral within a ski boot. Neutral in this context refers to the position of the subtalar joint of the ankle wherein the subtalar joint is neither pronated or supinated.  As acceptance of the neutral STJ paradigm grew, claims began to emerge implying that pronation was detrimental to skiing and could result in potentially injurious stress. I made a concerted effort to find explanations based on  principles of applied science and/or studies that supported these claims. But my efforts  failed to turn up anything significant even with the considerable resources of the National Research Council of Canada behind me. Where did these theories (they were exactly that) come from? Was there any rationale, let alone science behind them? Not as far as I could tell.

The ability to assume what I refer to as the SR Stance on skis is the prerequisite to the development of a solid technique. The single greatest factor influencing the ability to assume the SR Stance is the ski boot and especially any interventions introduced that influence the function of the foot and lower limb. Many of the widely accepted and promoted things that are done to the foot with a ski boot appear to have little or no support in principles of science. This is particularly true of interventions whose objective is to limit pronation or immobilize the joints of the foot in neutral.

The most likely roots of the neutral theory is The Biomechanical Examination of the Foot, Volume 1 by Merton Root, DPM and associates, DPM. Published in 1971, the book describes a set of eight “Biophysical Criteria for Normalcy,” which Root and associates ‘considered’ to be ideal values for normal foot function. Although the position of what is normal does not appear to be supported by studies, a definition of normal by a prominent podiatrist like Root inferred that feet that failed to meet Root’s criteria of normal required corrective interventions such as orthotics. Many podiatrists still commonly use these criteria to determine whether a foot is normal even though scientific research has never shown the biophysical criteria for normalcy that Root and coworkers proposed over three decades ago to be either ideal or an average range of foot and lower extremity structural parameters within the healthy human population.

According to Roots standards of normal, when a subject is standing on two feet (bipedal stance) with the weight of the body evenly distributed between both feet, the distal third of the leg should vertical to the supporting surface, the subtalar joint should rest in its neutral position where it is neither pronated or supinated and the calcaneal (heel bone) bisection should be vertical. Roots’ criteria of normal was meant for assessment purposes during an examination of the foot with the subject standing in a static position. To the best of my knowledge, Root never made any statement or claims to the effect that the foot functions best when its joints are immobilized in neutral, only that in a static examination position with the subject in bipedal stance, the subtalar joint should rest in its neutral position. It appears that the static examination definition of normal somehow morphed into the best functional configuration for skiing. From a functional perspective, it is a contradiction in terms to state that human foot, as one of the most dynamic structures in the body, will become optimally functional when it is rendered completely dysfunctional. If this were true, why stop at the foot? How about total body encapsulation?

The central issue, which everyone seems to be avoiding, is the process by which the 2 principle forces acting on a skier become aligned in opposition with each other utilizing ground reaction force from the snow to generate solid support between whole sole of foot and ground (snow). Everything else is just fluff. So why hasn’t this issue been addressed? Perhaps no one has been able to figure it out.