sports science

THE MECHANICS OF PLATFORM ANGLE: PART 1

In order to engage in an interactive productive dialog on issues pertaining to ski technique and related equipment a frame of reference based on validated, non-negotiable principles of physics, mechanics and (neuro)biomechanics as well as a schedule of defined reference terms such as exists in the sciences of mechanics, anatomy and physics is essential. Defined technical reference terms help ensure all participants in a discussion are on the same page.

I decided to start the new direction of The Skier’s Manifesto with a critical examination of the mechanics of platform angle starting with a schedule of the technical terms associated with platform angle and their definitions. Additional technical terms and their definitions will added in future posts according to the content of the discussion. The intent at this point is to start with a basic discussion of forces applied to a rigid body and/or surface (in this case, the surface of the snow) and then expand the scope of the discussion in future posts. Agreement on terms and definitions is important. So please comment if you feel one or more the following terms are inappropriate or inaccurate or should be expanded and/or refined.

Technical Terms associated with Platform Angle

  • Platform Angle: the angle of the transverse aspect of the body of the ski underfoot with the surface of the snow.
  • Edge Angle: the angle of the edge of the ski in relation to the plane of the transverse aspect of the body of the ski adjacent the edge.
  • Force: an unopposed interaction that will change the motion of an object. A force has both magnitude and direction, making it a vector quantity.
  • Force Vector: the magnitude and direction of a force.
  • Applied Force: a force applied to a rigid body or surface.
  • Reaction Force: a force that opposes a force applied to a rigid body or surface.
  • Normal Force: a force acting perpendicular to a rigid body or surface that is resisting a force applied to it.
  • Angular Force: a force applied to a rigid body or surface that is not normal (perpendicular) to the rigid body or surface to which the force is applied.
  • Angle of Attack: the angle an angular force forms with the rigid body or surface to which it is applied to.
  • Resultant Force: also known as Net Force, is a single force associated with torque obtained by combining a system of forces and torques acting on a rigid body.

Technical discussions of the forces associated with the angle of the platform with the snow typically show opposing resultant and ground reaction forces implying a state of balance of the forces acting on platform created by the outside ski underfoot.

Schematic diagrams showing forces acting on the platform created by the body of the ski underfoot often show two opposing forces in alignment with each other acting close to or at the axis point created the inside edge of the outside ski. Or diagrams may simply show opposing forces aligned with each other implying the existence of a state of equilibrium.

In my next post I will discuss whether the above force diagrams accurately reflect a state of equilibrium of the forces acting on the platform of the outside ski. Please join the conversation.

WHAT DOES HIRSCHER HAVE IN COMMON WITH BRIGNONE, WORLEY AND SHIFFRIN?

The short answer to this question is that the 4 racers share a stance with the muscles of the biokinetic chain in isometric contraction during what I term the Load Phase of a turn sequence and the ability to use the elastic recoil energy created during the Load Phase for acceleration.

One of the key visual cues of an isometric stance is an extended outside leg with small angles at the knee and ankle and a forward position of the pelvis. Another key visual cue is high hands with arms reaching forward as if the racer is trying to reach forward and hug a large barrel.

The screen shot below is of Marcel Hirscher in the December 16, 2018 Alta Bada GS that he won by 2.53 seconds.

The screen shot below is of Tessa Worley in the 2018-19 Soelden GS.

Reductionist Anatomy

A longer answer to the question posed by the title of this post, one that I will expand on in future posts, is that Hirscher, Brignone, Worely and Shiffrin are examples of the application of the principles of an emerging paradigm that is challenging the fundamental way in which muscular anatomy has long perceived muscles as separate systems with specific functions. In the new paradigm that has arisen out of recent discoveries muscles function in conjunction with the myofascial network as a wholly integrated system; one that responds and adapts to the stresses imposed on it. Since these discoveries are almost ten years old the odds are that the dominant technique of Hirscher, Brignone, Worely and Shiffrin is not by chance.

In previous posts, I described a stance based on isometric contraction as the SR Stance. SR is an abbreviation for the Stretch Reflex. Technically, a better term for the stretch reflex is the stretch-shorten cycle

The reason I chose SR for the name of the stance is that isometric contraction and the stretch reflex are not part of the narrative of ski technique. I discuss the three forms of muscle contraction in my post I-C-E: SR (2.) which I have recently updated.

The reason a ski stance based on isometric contraction provides a huge competitive advantage has to do with recent finding discussed in a 2009 article (1.) in which ultrasound imaging that allowed for quantitative assessment of the mechanisms for elastic energy storage and return at the ankle joint during human walking found that the Achilles tendon stores elastic energy as the mid stance phase progresses until the energy peaks in late midstance and is released to produce a rapid recoil with very high peak power output. The researchers named this the Catapult Mechanism (3.).

An important feature of the ankle ‘catapult mechanism’ is that the stretch and recoil of the Achilles tendon allows muscle fibers to remain nearly isometric producing high forces with very little mechanical work. In the isometric state, muscles expend much less metabolic energy to produce force when compared to muscles shortening in concentric (positive work) contractions.

Recent research has also found that during explosive movements, the contractile elements of a muscle remain in an isometric state to increase tension in the non-contractile components in an effort to produce higher levels of force. The enhanced stiffness from the contractile component can help the connective tissue rapidly store mechanical energy during the lengthening (recoil) phase delivering greater power output during the shortening phase. (4.), (5.)

What all this means is that the power advantage seen in racers like Hirscher, Brignone, Worely and Shiffrin results from an integrated system. But the human body can only function as an integrated system under conditions which allow multi-plane movement, something conventional ski boots intentionally interfere with.

In my next post I will start from what I see as the fundamental element of a ski stance based on isometric contraction and progress upward from there.


  1. It Pays to Have a Spring in Your Step – 2009 Gregory S. Sawicki1, Cara L. Lewis2, and Daniel P. Ferris2 – 1. Department of Ecology and Evolutionary Biology, Brown University, Providence, RI; and 2. School of Kinesiology, University of Michigan, Ann Arbor, MI
  2. https://wp.me/p3vZhu-1wT
  3. Fascial Fitness: Fascia oriented training for bodywork and movement therapies – Divo G. Muller, Robert Schleip 
  4. Cutting Edge: Training the Fascial Network (Part 1) by Pete McCall M.S.
  5. Cutting Edge: Training the Fascial Network (Part 2) by Pete McCall M.S.

 

ANALYZING SKIER/RACER PERFORMANCE

In my last post (1.), I showed photos of Tessa Worely, Federica Brignone and Mikaela Shiffrin with their outside legs extended with small angles at their knees and ankles and asked Why is their outside leg extended? What advantage does it give these racers? How does it affect their ability to load and control their outside ski? So far there has only been one comment that didn’t address the questions I posed.

……… the study of biomechanics by physical educators must include cause as well as effect relationships which exist between sequential joint motions of the performer and the motion of the inanimate objects which he or she wears, rides or manipulates.

All factors must be studied in terms of the skill objective. If problems are noted in the performance of the skill, where did they originate? Within the performer? Within the sport object? Both? What precise changes must be made to obtain the skill objectives? The answer to the last question leads directly to what is known as quality teaching. The directions for improvement given to the performer must be based on scientific and technical analysis of the total skill.

The above excerpts are from a book published in 1983 called ANALYSIS OF SPORT MOTION by John W. Northrip. 

….. quality teaching – coaching of neuromuscular skills in physical education should always be preceded by an analytical process where the professional physical educator synthesizes observations and theory from scientific and technical perspectives……It must be remembered that the teaching of physical education is an art with a basis in science.

 Adjustments during the teaching process to improve performance must be made in sequential motion pattern of the involved joints. Therefore, the student of physical education must have functional knowledge of anatomic kinesiology.

Fast forward to 1987.

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. 

Dr. med. H.W. Bar, Orthopedics-Sportsmedicine, member of GOTS, Murnau, West Germany (2.)

In my next post I will attempt to provide an explanation of the effect of extending the outside knee and ankle in the load phase of a turn and the role of equipment in enabling (or preventing) this action using the knowledge I have gleaned over the past 40 years.


  1. WHAT DO BRIGNONE, WORLEY AND SHIFFRIN HAVE IN COMMON?
  2. Der Schu im Sport

FEDERICA BRIGNONE: PURE PELVIC POWER

I haven’t had a chance to write posts for awhile. But Federica Brignone’s powerful performance in last Saturday’s Killington GS; one in which she showcased the power of the pelvis has served to inspire and motivate me. I dedicate this post to Federica Brignone and my Italian followers.

Molto Benne Federica, Molto Benne!

As a prelude, I normally study as much video as I can locate after a race in order to try and find the camera angles and clarity I need to do a proper analysis. But I could find very little video of the Killington GS. So please bear with lack of quality in some the images I will use in this post.

Right out of the Gate

As soon as Brignone came out of the start gate, extended her ankles and knees in the fall line and stood tall I knew she was going to stand tall on the podium.

A fraction of a second later, she flexed her ankles and knees while still in the fall line. This was very significant because it indicated to me that she has the ability to flex her ankles and move her shank about 12 or more degrees against low resistance within the shaft of her boots. I call this ankle-flex free play.

To find out why low resistance ankle flexion is important please read (or re-read) my post THE SHOCKING TRUTH ABOUT POWER STRAPS (1.), which remains my most viewed post ever. Then think about the implications of Brignone’s ability to extend her ankle and especially her knee for the position of COM in her pelvis in relation to her feet.

Here’s a hint: The femur is significantly longer than the tibia.

To be continued.


  1. https://wp.me/p3vZhu-UB

WHY TRYING TO COPY HIRSCHER AND SHIFFRIN’S MOVES DOESN’T WORK – PART 4

A central premise in skiing, especially in ski teaching and coaching, is that skiers and racers can learn to ski like the best by observing and copying them. Hence, articles and videos that talk in nebulous terms about good balance, an athletic stance, pressure control, steering, edging, extension, separation etc. as elements that, when blended together, will enable skiers and racers to ski like the Hirschers and Shiffrins of the world. If a racer who has undergone training in the system is not competitive or worse, suddenly becomes uncompetitive, the racer is typically blamed for not being strong enough or not pushing themselves hard enough or not taking enough risk or some other factor. In the end, the responsibility for lacklustre performance is conveniently assigned to the racer.

Ski boots are rarely considered a factor. So long as the boots are comfortable that is the only thing that matters. To suggest otherwise is to blame the equipment. This flies in the face of my experience. But until the skate study (1.) I had no reliable way of measuring and thus comparing performance.

The two pressure studies done in 1998 by the University of Ottawa with elite ski instructors provided an opportunity to compare the results of the studies to those of the 2012 skate study that I modified skates for. This study was also done by the University of Ottawa. Of the three studies:

  • One 1998 skier pressure study used three highly skilled ski instructors (CSIA level IV)
  • One 1998 skier pressure study used six internationally certified Canadian ski instructors.
  • The 2012 skate study used five competitive skaters.

The 1998 study with the six internationally certified Canadian ski instructors provided Peak Force data that I could use to compare to the Peak Force data obtained from the 2012 skate study.

As I pointed out in my previous posts, skating and skiing are similar in that they both depend on the ability of the participant’s neuromotor system to create a foundation of dynamic stability across the skate blade or the inside edge of the outside ski prior to being able to effectively apply force to the ice blade or ski edge. The existence of dynamic stability across the skate blade or inside edge of the outside ski enables the neuromotor system to regulate fore-aft stability in what is typically referred to as skater or skier balance.

Peak Force

Peak Force is the highest force applied in an Impulse Force

In the skate study skaters performed forward skating sprint starts in each skate (OS and NS) for a total of 6 trials each. As would be expected with competitive skaters Dynamic Stability as represented by Peak Force was very close among the skaters in their Own Skates as shown in the graphic below.

But when the highest and lowest Peak Forces of the competitive skaters were compared to the highest and lowest Peak Force of the internationally certified Canadian ski instructors the difference was much greater; approximately 125% for the skaters and 300% for the ski instructors. The researchers noted this significant variance and suggested equipment could have been a factor. But that aspect was not investigated.

Peak Force Improvement

It would seem logical to assign sole responsibility for such marked differences to inferior muscle strength or improper training. Muscle strength and training are definitely important factors. But their contribution to overall performance is dependent on the ability of a competitor to create dynamic stability and quickly acquire a position from which they can effectively apply force to a skate blade or edges of a ski. These factors, in turn, are dependent on a functional environment in the footwear for the physiogic function of the lower limb.

As shown in the graphic below, when the same skaters switched from their Own Skates (OS) to the skates I prepared (NS) there was an immediate and statistically significant improvement in mean Peak Force of approximately 190%. Even more significant is the fact that the Peak Force of skater number 4 (the lowest of the four skaters) increased by approximately 252% changing the skater’s ranking from #4 to #1.

Impulse Force Improvement

An Impulse Force is a high force of short duration that causes a change in momentum.

When the skaters switched from their Own Skates (OS) to the New Skates (NS) there was an immediate mean increase in Impulse Force of approximately 216% as shown in the graphic below. Even more significant, the Impulse Force of skater number 4 (the lowest of the four skaters in their Own Skates) increased by approximately 276% raising skater number 4 to almost the same level as skater number 3. Meanwhile, an increase in Impulse Force of approximately 224% raised skater number 2 to almost the same level as skater number 1. In other words, the New Skate was literally a game changer that resulted in a leveler playing field for the four competitive skaters.

Center of Force (CoF) Variance: Where Races are Really Won

The most significant effect of the New Skate (NS) was on what is called Center of Force (CoF) Variance. Center of Force Variance is the amount of forward movement of the Center of Force within a fixed unit of time to the position on a skate blade or ski edge where force can effectively be applied.

The graphic below shows the Center of Force Variance of the four competitive skaters in their own skates (OS).

The graphic below shows the Center of Force Variance of the four competitive skaters in their Own Skates (OS) compared to the Center of Force Variance in the new skates (NS). When the skaters switched from their Own Skates (OS) to the New Skates (NS) there was an immediate mean increase in CoF Variance of approximately 172% as shown in the graphic below. Skater number 4 experienced the largest increase in CoF Variance (approximately 241%) that changed the ranking from #3 to #1.

An increase in the variance of CoF results in increased control during the stance phase of forward skating.

The graphic below shows what would happen if only skater number four were provided with New Skates (NS) while the other 3 competitive skaters continued to use their Own Skates (OS). Think of the red dashed line at 1.20 as the finish line of the CoF Variance race. It should obvious who will win and who will have the advantage at every turn.

The Score for Skater Four

Skater number four experienced the following improvements in the New Skates (NS) over their Own Skates (OS)

  • Peak Force – 252%
  • Impulse – 276%
  • CoF Variance – 241%
  • Mean improvement – 256%

The improvement in the three metrics was immediate and, based on my experience with skiers and racers, probably immediately reversible simply by having the competitive skaters revert to their Own Skate (OS) format.

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.)

To paraphrase Dr. Emily Splichal:

A skier is only as strong as they are dynamically stable.

In my next post, I will discuss the implications of the skate study and associated performance technology and metrics for the future of skiing, especially ski racing.


  1. A Novel Protocol for Assessing Skating Performance in Ice Hockey – Kendall M, Zanetti K, & Hoshizaki TB – School of Human Kinetics, University of Ottawa. Ottawa, Canada
  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

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

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

There appears to be a widely held perception within the ski industry, even among coaches and trainers at the World Cup level, that skiing like Hirscher and Shiffrin is simply a matter of observing and then copying their movements. There also appears to be a widely held perception that strength training and training on BOSU balls, wobble boards, slack lines and thick foam pads will transfer to improved balance on skis.

In a recent article, Nailing the Coffin Shut on Instability Training Ideas (1.), trainer, Bob Alejo, cites 59 papers on the topic of instability training in support of his position that not only are the assumptions about instability training improving balance in a specific activity incorrect, instability training may actually have a negative effect on performance.

As far back as 1980, I had found that an immediate improvement in skier performance after ski boot modifications was a reliable indicator that the modifications were positive. Sometimes this was evident in the first few turns. I had also found that equipment modifications or equipment changes that had a negative effect did not become obvious right away. I didn’t understand the reason for the immediate and sometimes dramatic improvement in skier performance following ski boot modifications. But I suspected it had something to do with improved skier balance.

By 1990, I had hypothesized that elite skiers are able to create a dynamically stable foundation under their outside ski and foot in a turn to balance on by rotating the edged ski against resistance from the sidecut and that this has the effect of extending ground reaction force from the snow out under the body of the ski. But even after the Birdcage studies of 1991 validated my theory, I still didn’t fully understand the reason for the dramatic improvement in skier performance in the Birdcage tests or following modifications made to conventional ski boots. Strain gauges fit to the Birdcage showed forces and the sequence of loading. But the strain gauges could not measure the magnitude of the forces.

It was Dr Emily Splichal’s (2.) that answered my question when she said;

It doesn’t matter how physically strong you are. Without a foundation of stability, you are weak. With a foundation of stability, you are stronger and faster than anyone.

In his article, Nailing the Coffin Shut on Instability Training Ideas (1.), Alejo supports Dr. Splichal’s position:

The predominant theme of the training data analysis under unstable conditions is the striking reduction in force and, subsequently, power. It would be of no surprise then that the speed of motion, as well as the range of motion, were negatively affected under unstable conditions, as cited in the literature.

Reduced Force Outputs Result in Less Power

Essentially, even though both groups improved in some instances, the stable surfaces group outperformed the unstable group in all categories. So much so that it led the authors to conclude that the results of their study affirmed—what was a criticism then and now is fact—that unstable training does not allow for enough loading to create strength and data.

Simply put, athletes can handle heavier weight under stable conditions versus unstable conditions.

Dynamic Stability is critical for a skier or skater to assume a strong position from which to generate force while maintaining control and initiate precise movement from. A key marker of dynamic stability in ice skating and skiing is the magnitude of impulse force, especially peak force.

Impulse

Impulse is a large force applied for a short duration of time. Peak force is the highest force applied during an impulse force.

If superior dynamic stability is the reason for the dominance of racers like Hirscher and Shiffrin then pressure data obtained during skiing should show higher impulse and peak forces than generated their competition. While the technology to measure these forces is readily available I don’t have access to this data even if it does exist. So I’ll use data generated from hockey skate study I was involved in 2012 that compared data captured from competitive skaters performing in their own skates to skates I had modified using principles from my patents and modifications described in this blog.

The first step was to capture baseline data from the test subjects own ice skates (OS). The bar graph below shows the peak force in Newtons applied by each of the four test subjects. Peak force has a very short duration.

Subjects 1 and 3 applied a peak force of approximately 800 Newtons. A pound is 4.45 Newtons. So 800 Newtons is approximately 180 lbs.

Test subjects #1 and #3 are almost identical. But test subject #1 has a very slim edge over test subject #3.

Test subject #2 is 3rd in ranking while test subject #4 is last.

Assuming this was a study of competitive skier test subject #1 appears to have a stability advantage over the other skiers. This would translate into quicker more precise turns (hairpin turns) and less time on their edges.

In my next post I will show what happened when the same test subjects used the skates I prepared.


  1. Nailing the Coffin Shut on Instability Training Ideas – https://simplifaster.com/articles/instability-training/