biomechanics

THE 2018 SOELDEN GS: A LITMUS TEST OF DYNAMIC STABILITY

Challenging  course conditions, especially in GS, are the litmus test of dynamic stability. The 2018 World Cup GS at Soelden had challenging conditions in spades.

The ability to rapidly achieve dynamic stability across the inside edge of the outside ski is key to moving the Center of Force forward to the point where the biokinetic chain of the outside leg attains sufficient tension to enable the stretch reflex. The stretch reflex (SR) can then modulate pertubations due to asperities in snow surface and terrain with ankle strategies. The principle muscle in ankle balance synergies is the soleus. Dynamic stability enables a racer to float between turns, accelerate under gravity then land on line and load the outside ski. A racer with good dynamic stability is on and off the edges in milliseconds and back into the float phase. Like a skilled gymnast elite skiers and racers can choose their line and stick their landing. Tessa Worely excelled at this in the 2018 Soelden GS.

Tell Tale Signs of Dynamic Stability

Key indicators of dynamic stability are a quiet upper body and the speed at which a racer achieves their line and crosses over into the new turn with their upper body. It’s like watching a flat rock thrown low skipping off water; fly-skip-fly-skip.

In my post, WHY YOUNG TALENTED SKI RACERS FAIL AND EVENTUALLY QUIT RACING (1.), I discuss the 3 levels of balance:

  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).

If a racer is no able to use the myotatic reflex (Green = Normal) balance response, the CNS shifts to Level 2 (Orange = Caution) or even Level 3 (Red = DANGER).

Level 1 balance is characterized by a stable, well-controlled upper body (aka quiet upper body) with well controlled and directed positions of the arms.

When the myotatic (stretch) reflex is compromised by restriction of the ankle flexion range required to tension the soleus the balance system will shift to level 2 or level 3 depending on the degree of interference. As the degree of interference with required range of ankle flexion increases the degree of reflexive balance will progress from small, rapid, reactive arm movements to gross reactive arm movements that eventually include gross movements of the torso.

The authors of the Polish skier balance study cited in my post state that ski boots exclude the ankle joint complex from the process of maintaining the stability of the body. However, I don’t believe this is the case with all skiers and especially all racers as evidenced by Soelden video of Tessa Worley, Federica Brignone and Michaela Shiffrin. In my next post I will discuss what I look for in analyzing that suggests dynamic stability and especially a lack of dynamic stability and the indications of compromise and the potential cause.

In the meantime, here’s something to think about.

Early in my boot modification career I came to the conclusion that some skiers, especially racers, were born with the right shape of feet and legs (2.) and this explained why they could ski in ski boots right out of the box with minimal or no modifications better than the majority of skiers even after extensive boot modifications. In a recent series of posts I discussed the results of the 2012 skate study that I modified hockey skates for; the NS (New Skates – Blue bars in the graphics below). The modifications I made were based on ski boot modifications that had resulted in dramatic improvement in performance and race results. Although I optimistically predicted improvements in performance metrics of at least 10% (110%) based on my experience with World Cup skiers, I knew that there was the possibility of a wild card competitive skater who was already close to their maximum performance in their OS (Own Skates – Red bars in the graphics below). If this were the case the skater would realize minimal improvement from the New Skates.

My previous posts only included the results for four competitive skaters. There were actually five competitive skaters in the study. Skater number 1 was the wild card. Look what happened to the results when the wild card skater was added.Look carefully at the graph of the Impulse Force below. Compare Skater number one’s Impulse Force results with the Peak Force results in the preceding graph.This raises the question: Do Tessa Worely, Federica Brignone, Mikaela Shiffrin and other top World Cup racers have the right shape of feet and legs or do they have the right modifications made to their ski boots.


  1. (https://skimoves.me/2017/02/15/why-young-talented-ski-racers-fail-and-eventually-quit-racing/)
  2. THE IDEAL SKIER’S FOOT AND LEG – https://wp.me/p3vZhu-qf

 

 

 

WHY TRYING TO COPY HIRSCHER AND SHIFFRIN’S MOVES DOESN’T WORK – PART 2

In previous posts I discussed the two studies (1, 2) done by the University of Ottawa in 1998 that analyzed pressure under the feet of elite alpine ski instructors

The pressure data from the study that used 6 elite alpine ski instructors found maximal (peak) force ranged from a high of 1454 Newtons to a low of 522 Newtons. The graph below compares the peak force seen in pressure data captured from the 4 competitive skaters in their own skates from my last post to the highest and lowest peak force seen in pressure data captured from the 6 elite alpine ski instructors used in the 1998 University of Ottawa study.

In consideration of the fact that the researchers commented that force-time histories revealed that forces of up to 3 times body weight can be attained during high performance recreational skiing it is interesting that the peak force of one of the 6 elite alpine ski instructors in the study was less than the lowest peak force of one of the 4 competitive skaters in the 2012 University of Ottawa study while the highest peak force of one of the 6 elite alpine ski instructors in the 1998 study was almost twice the highest peak force of one of the 4 competitive skaters in the 2012 University of Ottawa study.

A significant challenge in attempting to conduct foot pressure studies with alpine skiers is the variability of the slope and environmental and piste conditions. Test conditions and variables, especially ice, can be tightly controlled in the conditioned environment of an indoor skating rink.

Although the studies did not provide pressure data that compared peak and average pressures for different ski instructors, the peak forces from one study reached up to 30 newtons per square centimetre.

In the spring of 2012 I was asked to modify a number of pairs of the same brand and model of a hockey skate for use in a study that would compare metrics derived from pressure data captured from a competitive skater’s own skates to the same metrics from data acquired  from skates I had modified. I saw this as an opportunity to document the effect of modifications made to hockey skates based on the principles of neurobiomechanics described in my patents and this blog. When I speculated that the metrics derived from the pressure data might show improvements as high as 10% (i.e. 110%) I was told that the study was unlikely to result in more than a single digit improvement of approximately 2% or 3%.

I modified the pairs of skates in the shop in the garage of my home near Vancouver. The modifications were general in nature and made without the benefit of data on the feet of the test subjects. No modifications were made after I shipped the hockey skates to the University of Ottawa. I was not involved in the design of the study protocol or the actual study. I was hopeful that the study would produce meaningful results because it would have implications that could be extrapolated to alpine skiing.

The graph below shows the highest peak force in Newtons recorded for each of the 4 competitive skaters in their own hockey skates (blue = OS) and in the hockey skates that I modified (red = NS). The improvement was immediate with little or no run in period in which to adapt. The percentage improvement for each skater is shown at the top of each bar.

The mean (i.e. average) improvement was approximately 190%. The only factor that improvements of this magnitude could be attributed to is improved dynamic stability resulting from an improved functional environment in the skate for the foot and leg of the user.

……. to be continued in Part 3.


  1.  ANALYSIS OF THE DISTRIBUTION OF PRESSURES UNDER THE FEET OF ELITE ALPINE SKI INSTRUCTORS – Dany Lafontaine, M.Sc.1,2,3, Mario Lamontagne, Ph.D., Daniel Dupuis, M.Sc.1,2, Binta Diallo, B.Sc.: Faculty of Health Sciences1, School of Human Kinetics, Department of Cellular and Molecular Medicine, Anatomy program, University of Ottawa, Ottawa, Ontario, Canada.
  2. ANALYSIS OF THE DISTRIBUTION OF PRESSURE UNDER THE FEET OF ELITE ALPINE SKI INSTRUCTORS – Dany Lafontaine, Mario Lamontagne, Daniel Dupuis, Binta Diallo, University of Ottawa, Ottawa, Ontario, Canada

THE HIRSCHER/SHIFFRIN HAIRPIN TURN EXPLAINED

The topics of interest in recent views of my blog combined with comments on online forums on ski technique where nebulous terms such as pressure and tipping are an integral part of the narrative, have highlighted the need for a uniform frame of reference as a basis for meaningful discussions of ski technique as well as for the analysis and accurate identification of factors that explain the superior technique of racers like Marcel Hirscher and Mikaela Shiffrin. Simply trying to emulate the moves of the great skiers without re-creating the equipment factors that enable superior performance is not a productive exercise.

I touched on some of the factors that enable Marcel Hirscher and Mikaela Shiffrin to dominate their competition in my posts WHY SHIFFRIN AND HIRSCHER ARE DOMINATING (1.) and WHY HIRSCHER AND SHIFFRIN CAN CROSS THE LINE (2.). Over the coming weeks, I will post on the factors that I believe explain the ability of Hirscher and Shiffrin to make rapid, abbreviated hairpin turns even on the steep pitches of a course using what I call the problem-solving matrix jigsaw puzzle format. In contrast to the linear step-by-step progression problem-solving format, the matrix jigsaw puzzle format lays out information relevant to a situation in a grid format much like a jigsaw puzzle.  Known factors are assembled where there is a fit with the interfaces and arranged in relation to other components until a solution begins to emerge much like a coherent picture begins to emerge in a jigsaw puzzle as the pieces are correctly assembled. As the picture becomes more clear, tentative connections between the known segments are hypothesized to try and extrapolate the big picture. As the process progresses, less certain or flawed information is discarded and replaced with more certain information

A lot of critical information on the neurobiomechanics and even the mechanics and physics of skiing is either missing, misapplied or misunderstood in the narrative of ski equipment and technique.

Biomechanics of Sports Shoes

A valuable reference on neurobiomechanics and the future of sports shoes is the technical text, Biomechanics of Sports Shoes by Benno M. Nigg. Used in conjunction with the chapter on the Ski Boot in the medical text, The Shoe in Sport, valuable insights can be gleaned on the mechanics, neurobiomechanics and physics of skiing.

Nigg’s book can be ordered at NiggShoeBook@kin.ucalgary.ca. The following chapters in particular contain information relevant to skiing:

3. Functional Biomechanics of the Lower Extremities (pp 79 to 123) – contains essential information on the human ankle joint complex, tibial rotation movement coupling and foot torsion.

4. Sensory System of the Lower Extremities (pp 243 to 253) – contains essential information on the sensory system responsible for balance and precise movement, both of which are key to effective skiing.

In order to advance skiing as a science, a mutual objective must be getting the right answer as opposed to a need to be right.

The wisdom of Albert Einstein is appropriate.

A man should look for what is, and not for what he thinks should be.

To raise new questions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks real advance in science.

We cannot solve our problems with the same thinking we used when we created them.

If you can’t explain it simply, you don’t understand it well enough.

In my next post, I will start laying out the functional principles that I currently believe explain the factors that enable the superior performance of racers like Marcel Hirscher and Mikaela Shiffrin and their ability to rapidly redirect their line and maximally accelerate by making rapid, abbreviated, hairpin turns.


  1. https://wp.me/p3vZhu-2q3
  2. https://wp.me/p3vZhu-2qo

TIGHTLY FIT SKI BOOTS COMPROMISE SKIER BALANCE AND CONTROL

In reviewing recent articles on ski boot fitting I encountered the same perfect fit of the boot with the shape of the foot and leg and ski boots must be tightly buckled for good balance and control narrative fabricated decades ago to justify the interference with the actions of the joints of the ankle and leg created by the rigid plastic shell ski boot.

When the first rigid shell plastic ski boots were introduced, the field of biomechanics, as it exists today, was in its infancy. Even until recently, the human foot was modelled as a rigid block which was consistent with the shoe last theory and the theory that the perfect fit of ski boots with the foot and leg of the user is the best option for skiing. Further support for the support and immobilize theory came from the vilification of pronation arising out of the misapplication of Root’s Neutral theory (1.)

By the time the authoritative medical text, The Shoe in Sport, was published in 1987, the knowledge of the biomechanics of the human foot had progressed to the point where tight-fitting ski boots and loading the ankle joint were recognized as unphysiologic.

Few forms of athletics place as high demands on the footwear used in their performance as alpine skiing. It (the ski boot) functions as a connecting link between the binding and the body and performs a series of difficult complex tasks. (2.)

Investigations by Pfeiffer have shown that the foot maintains some spontaneous mobility in the ski boot. Thus the total immobilization by foam injection or compression by tight buckles are unphysiologic.(2.)

Many alpine skiers have insufficient mobility in their knees and ankle. The range of motion, particularly in the ankles, is much too small.(2.)

From a technical (skiing) point of view, the ski boot must represent an interface between the human body and the ski. This implies first of all an exchange of steering function, i.e., the skier must be able to steer as well as possible, but must also have a direct (neural) feedback from the ski and from the ground (snow). In this way, the skier can adapt to the requirements of the skiing surface and snow conditions. These conditions can be met if the height, stiffness, angle and functions (rotational axes, ankle joint (AJ)/shaft) of the shaft are adapted, as well as possible to the individual skier. (3.)

The articles on ski boots in the Shoe in Sport identified the objectives I was seeking in my efforts to design a ski boot based on principles of what is now referred to as neurobiomechanics. By the time I had formulated my hypothetical model of the mechanics, biomechanics and physics of skiing in 1991 I understood the need to restrain the foot in contact with the base of a ski boot and maintain the position of the foot’s key mechanical points in relation to the ski while accommodating the aspects of neurobiomechanical function of the foot and leg required for skiing. This was the underlying theme of the US patent that I wrote in February of 1992.

Existing footwear does not provide for the dynamic nature of the architecture of the foot by providing a fit system with dynamic and predictable qualities to substantially match those of the foot and lower leg. – US patent No. 5,265,350: MacPhail

On June 2, 2013 I published the post TIGHT FEET, LOOSE BOOTS – LOOSE FEET, TIGHT BOOTS (4.) in which I describe how attempts to secure the foot to a ski in a manner that interferes with the physiologic mechanisms that fascially tension and stiffen the structures of the foot that render it dynamically rigid actually reduce the integrity of the joint system of the lower limbs and hips resulting in a looser connection with the ski.

Studies done in recent years confirm the role of the active state of the architecture and physiology of the foot to postural control and balance.

These findings show that rather than serving as a rigid base of support, the foot is compliant, in an active state, and sensitive to minute deformations. In conclusion, the architecture and physiology of the foot appear to contribute to the task of bipedal postural control with great sensitivity. (5.)

The science of neurobiomechanics and the understanding of the mechanisms of balance and the role of the sensory system in human movement is accelerating. The time is long overdue for skiing to abandon it’s outdated concepts and align it’s thinking with the current state of knowledge.


  1. IS ‘SUBTALAR NEUTRAL’ SKIINGS’ HOUSE OF CARDS? – https://wp.me/p3vZhu-2mn
  2. Ski-Specific Injuries and Overload Problems – Orthopedic Design of the Ski Boot –  Dr. med. H.W. Bar, Orthopedics-Sportsmedicine, member of GOTS, Murnau, West Germany
  3. Biomechanical Considerations of the Ski Boot (Alpine) – Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland
  4. https://wp.me/p3vZhu-2K
  5. Foot anatomy specialization for postural sensation and control

WHAT’S YOUR PQ? [PERFORMANCE QUOTIENT]

After my disastrous experience in 1977 with the mythical Perfect Fit with Crazy Canuck, Dave Murray (.1); one that transformed Mur from a World Cup racer to a struggling beginner, my work on ski boots became focussed on removing instead of adding material and making room to allow a skier’s foot to assume its natural configuration in the shell of the ski boot. As I improved the accommodation of a skiers’ neurobiomechanical functional requirements in the ski boot, skier performance improved in lockstep. I was merely reducing the structures of the boot that interfered with performance to enable a skier/racer to use the performance they already had.

Fit: The Antithesis of Human Function

Fit, by it’s definition of joining or causing to join together two or more elements so as to form a whole, is the antithesis (def: the direct opposite) of enabling the function of the human foot and lower limbs as one of the most dynamic organs in the human body. Fitting a ski boot to the foot and leg of a skier, especially a racer, equates with imposing a disability on them (2.). Although I didn’t realize it until I read The Shoe in Sport and learned of the barefoot studies done at the Human Performance Laboratory at the University of Calgary, my work on ski boots had transitioned from Fitting (disabling), by adding materials to liners to fill voids between the foot and leg and shell wall, to UnFitting (abling) by removing materials from liners and expanding and grinding boot shells so as to accommodate the neurobiomechanical functional requirements of the foot and leg of a skier.

But the big breakthrough for me came when Steve Podborksi won the 1981-81 World Cup Downhill title using the dorsal constraint system (Dorthotic) I developed and later patented. The Lange boot shells the device was used in had the least constraint of any ski boot I had ever worked with. The instantaneous quantum leap in Steve’s performance compared to the same shell using a conventional liner raised the question of how could a skier’s maximum performance be achieved and was there a way to compare to a skier’s performance in different ski boot/liner configurations to an optimal reference standard?

A reliable indicator that my un-fitting was trending in the right direction was that skiers consistently found that skiing became easier. For racers, coaches would typically report that the racer was skiing better. Improved race results served as further confirmation of my efforts. But these indicators were subjective. I wanted a way to not just measure performance with quantifiable metrics generated from data specific to the activity, I wanted to be able to compare the same metrics to a reference or baseline standard that represented the optimal performance of a skier or racer at a given moment in time. Without a way to measure and compare performance there is no way of knowing how a ski boot is affecting a skier or racer and especially no way of knowing how close they are to skiing at their maximum level of performance. I wanted to develop a skier Performance Quotient or PQ.

Definition of Quotient

  • Mathematics: – a result obtained by dividing one quantity by another.
  • a degree or amount of a specified quality or characteristic.

A skier Performance Quotient would capture baseline metrics from a skier’s performance in a ski boot that provides the optimal functional environment for the foot and lower limbs to the skier’s peformance in different ski boots including a skier’s current ski boot. The ski boot that provides the optimal functional environment for the foot and lower limbs would be designated as 100%. If the same metrics captured in a different ski boot were 78% of the reference standard, the skier’s PQ in the ski boot would represent a PQ of 78% against a possible 100% or 78/100.

Raising the bar of skier/racer function with body work and/or conditioning will raise the PQ. But it cannot close the PQ gap created by the performance limitations of the interference with neurobiomechanical function caused by their ski boot. Nor can trying harder or training more intensely overcome the limitations of a ski boot. Assuming 2 ski racers of equal athletic ability and mental strength, the racer with the ski boot that enables a higher PQ will dominate in competition. The only way to improve a skier’s PQ when it is less than 100% is to improve the functional environment of the ski boot.

In current ski boot design process, manufacturing and aesthetic considerations override skier functional requirements. An innovative approach to the design of the ski boot is needed. This is the subject of my next post.


  1. IN THE BEGINNING: HOW I GOT STARTED IN SKI BOOT MODIFICATIONS, May 12, 2013 – https://wp.me/p3vZhu-y
  2. LESS REALLY IS MORE, May 13, 2013 – https://wp.me/p3vZhu-N

 

(NEURAL) BIO (MECHANICAL) ENGINEERING: DOES IT WORK?

The proof of a performance concept lies in the data. If neural bio mechanical engineering can improve human performance in a specific application such as skiing, skating or cycling then it should be possible to demonstrate meaningful performance improvement with quantifiable metrics generated from data captured from the actual activity. In the case of cycling, meaningful improvement would be shown by an increase in metrics such as peak force transferred to the pedal spindle that cannot be explained by other factors. In order to attribute any change in performance, whether positive or negative, to neural bio mechanical engineering the effect must be immediate, reversible and reproducible. In the case of the improvement seen with Podborski’s performance using ski boots fit with the dorsal fit system, reverting to identical boot shells fit with a conventional liner reversed the improvement in performance.

Where possible, standard protocols should be used and testing performed by experts in the field. In the case of the cycling shoe Tekscan F Scan data comparison, my only involvement was to analyze the human lower limb requirements for cycling and generate the design and specification for the device that produced the neural bio mechanical engineering effect. I played no role in designing the test protocol or conducting the tests. I was not even an observer.

So how did the neural bio mechanical engineering system work in the application to cycling?

Performance Metrics

There are numerous metrics that can be used to assess and compare performance. The subject test was limited to pressure analysis using the Tekscan F Scan system.

In the graphic below the upper image outlined in red is the F Scan pressure image of an elite cyclist captured at 3 o’clock in the crank cycle at moderate to high load using their own conventional cycling shoe. The F Scan pressure image outlined in green below the first image is of the same cyclist using the device that bio engineered the foot and lower limb.

Results

There are a number of significant differences between the forces applied with the same cyclist with the conventional cycling shoe and the bio-engineering. In the 2 F Scan images, the contact area of the application of force across the heads of the metatarsals over the pedal spindle with bio-engineering is much greater and the force much higher than the force applied to the heads of the metatarsals in the conventional shoe.

The two significant, quantifiable (measurable) metrics that relate directly to cycling performance are: Peak Force and Anterior-Posterior (forward-backward) Excursion of the Center of Force.

Peak Force

The peak (maximum) force with the device that bio-engineered the foot and lower limb was 140% of the peak force applied with the conventional cycling shoe.

Anterior-Posterior (fore-aft) Force Excursion

This is the range of forward-backward movement of center of force through the crank cycle.

The graphic below shows the tracking of center of force forward and backward in the pedal stroke. Notice how straight the force tracks in the lower image with bio engineering compared to the upper image captured from the conventional cycling shoe.

The ability to move the center of force forward and backward, not just down and, more important, substantially aligned with the crank rotation is both more consistent and efficient than the excursion tracking with the conventional shoe. The bio engineering device improved excursion by 175% in rearward tracking force (long bars) and 200% in forward tracking force (over the top) as shown by the short bars below the images.

In my next post I will discuss how I designed a ski boot from the snow up using principles of neural bio-mechanical engineering.

INTRODUCTION TO (NEURAL) BIO (MECHANICAL) ENGINEERING

Neural biomechanical engineering is an external, non-invasive, reversible process that alters the neuralbiomechanics of the human feet and lower limbs in a manner that makes their function specific to an activity such as skiing, skating or cycling. In some cases, the process can potentiate muscle power and/or the processes of balance. Neural biomechanical engineering is human function centric.

The graphic below is the pressure image of the right foot of the same elite cyclist in the last post except that the foot has undergone neural biomechanical engineering.Red is highest force. Dark blue is the lowest force. Forces were recorded with a Tekscan F Scan system fit to the shoe.

The highest primary forces are now across the heads of all five metatarsals with secondary forces under the big toe and, to a lesser extent, the second and third toes. The primary force is now applied to the pedal spindle. The applied force is also more focussed under the heel.

There are many other more subtle but important changes. But the central issue is whether metrics show a significant quantifiable improvement in performance.

What, if any, improvement in performance resulted from the application of neural biomechanical engineering? Any guesses?