Skier Stance

WHAT DO BRIGNONE, WORLEY AND SHIFFRIN HAVE IN COMMON?

Results tell the story

Soelden GS – 10/27/2018

  1. Tessa Worley –  2:00.51
  2. Federica Brignone – +0.35
  3. Mikaela Shiffrin – + 0.94

What do you see?

Tessa Worley

 

Federica Brignone

 

Mikaela Shiffrin

Killington GS – 11/24/2018

  1. Federica Brignone

Federica Brignone

Study the photos. Note that all the racers have their outside extended with a small angle at the knee. The question I will begin to address in my next post is why is the outside leg extended. What advantage does it give these racers? How does it affect their ability to load and control  their outside ski?

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

LEARN THE SR STANCE IN 3 EASY STEPS

This post was originally published on October 23, 2016. I have revised the post to clarify that the SR Stance applies to the load phase of a turn that occurs in what is commonly referred to as the bottom of a turn and that the joint angles of the SR Stance are configured by the major muscles in isometric contraction. When external forces cause the muscles to lengthen or stretch this will trigger the myotatic or stretch reflex. Because the myotactic reflex is a spinal reflex it is activated in 1 to 2 thousandths of a second. As such, it is both rapid and powerful.


The SR Stance configures some of the most powerful muscles in the body in a state of isometric contraction so that the powerful myotactic stretch reflex can maintain the angles of the ankle, knee, and hip and keep the CoM of a skier in balance on their outside ski in the most powerful position in the load phase of a turn.

The SR Stance is best learned outside the ski boot in an environment where the feet and legs are free from any influences. One of the benefits of learning an SR Stance outside the ski boot is that, once learned, it provides a reference against which to assess whether a ski boot supports the functional parameters of the skier. If it doesn’t, the SR Stance can be used as a reference to guide equipment modification and establish when and if it meets the functional requirements of the skier.

The SR Stance tensions the pelvis from below and above; below from the balls of the feet through the PA-soleus-gastrocnemius-hamstring muscles to the pelvis and above from the shoulders-latissimus dorsi-trapezius muscles to the pelvis.

The graphic below shows the Achilles Tendon junction with the PA at the heel bone.

pa-ac

The graphic below shows the 3 major muscles of the leg associated with the SR stance.

3-muscles

The Soleus (left image in the above graphic) extends from the back of the heel bone (see previous graphic) to a point just below the knee. It acts in concentric contraction (shortening) to extend or plantarflex the ankle. In EC-SR, the Soleus is under tension in stretch in isometric contraction.

The Soleus is one two muscles that make up the Triceps Surae.

The Gastrocnemius (center image in the above graphic) extends from the back of the heel bone  to a point just above the knee. It acts in concentric contraction (shortening) to flex the knee. In EC-SR, it is under tension in isometric contraction to oppose extension of the knee.

The Hamstrings (right image in the black rectangle in the above graphic) extends from a point just below the knee to the pelvic girdle. It acts in concentric contraction (shortening) to flex the knee. In EC-SR, it is under tension in isometric contraction to oppose extension of the knee.

A number of smaller muscles associated with the SR that will be discussed in future posts.

The graphic below depicts the 3 steps to learning an SR Stance.

er-steps

  1. The first step is to set up a static preload on the shank (shin) of the leg by tensioning the soleus muscle to the point where it goes into isometric contraction and arrests ankle dorsiflexion.

The static preload occurs when the tension in the soleus muscle of the leg simultaneously peaks with the tension in the sheet-like ligament called the plantar aponeurosis (PA). The PA supports the vault of the arch of the foot. The soleus is an extension of the PA. This was discussed in my post ZEPPA-DELTA ANGLE AND THE STRETCH REFLEX.

  • While barefoot, stand erect on a hard, flat, level surface as shown in the left hand figure in the graphics above and below. The weight should be felt more under the heels than under the forefoot.
  • Relax the major muscles in the back of the legs (mainly the hamstrings) and allow the hips to drop and the knees to move forward as shown in the right hand figure in the graphics above (1.) and below.
  • As the knees move forward and the hips drop towards the floor the ankle joint will dorsiflex and the angle the shank forms with the floor and the angle of the knee, will both increase until a point is reached where the shank stops moving forward on its own. Movement of the shank will probably be arrested at a point where a plumb line extending downward from the knee cap ends up slightly ahead of the foot. This is the static preload shank angle. It is the point where the soleus and quadriceps muscles go into isometric contraction.

static-preload

2. From the static preload shank angle, while keeping the spine straight, bend forward slightly at the waist. The angles of the shank (ankles) and knees will decrease as the pelvis moves up and back and the CoM moves forward towards the balls of the feet. This will cause the muscles of the thigh to shift from the Quadriceps to the Hamstrings. Bending at the waist tilts the pelvis forward. As the pelvis tilts forward, it tensions the Hamstrings and Gastrocnemius causing the knee and ankle to extend to a point where extension is arrested by the muscles going into isometric contraction. Tension in the Hamstrings and Gastrocnemius extends the lever arm acting to compress the vault of the arches of the feet from the top of the shank to the pelvis thus increasing the pressure on the balls of the feet through Achilles-PA load transfer.

3. From the position in 2., round the back and shoulders as you bend forward from the waist.

Shldrs-back

Make sure the core is activated and tightened as you round the back and shoulders. Pull the shoulders forward and towards each other as the back is rounded so as to form a bow with the shoulder girdle. Looking down from above, the arms should look like they are hugging a large barrel.

Repeat steps 1 through 3. Pay close attention to the changes in the sensations in your body as you work through each step. If you bounce up and down lightly in the position in Step 3., the angles of the joints in your stance should return to the static preload position between bounces.

With the ski boot and Zeppa-Delta ramp angles configured to enable an SR stance, your ski boots will work for you and with you instead of the other way around.

In my next post, I will go into greater detail on how rounding the shoulders and holding the arms in the correct position optimally activates the muscles associated with the SR stance.

IS ‘SUBTALAR NEUTRAL’ SKIINGS’ HOUSE OF CARDS?

If you purchased custom footbeds for your ski boots or had your ski boots custom fit you may have been told that your foot was placed in subtalar neutral and that this created the strongest position of the bones of the foot and leg for skiing. Neutral in this context refers to a neutral configuration of the subtalar joint of the ankle/foot complex.

As best I can recall, the term subtalar neutral began to emerge in the ski industry about 1978. The authoritarian manner in which it was presented and promoted suggested that it was science-based and supported with evidence that conclusively demonstrated superior performance. But I never saw or heard any explanation as to how subtalar neutral could create the strongest position for skiing of the bones of the foot and leg and I have still not seen such an explanation.

Back in 1978, I didn’t even know what the subtalar joint was. I couldn’t envision how the bones of the foot and leg could be maintained in a specific configuration while foam was injected into a liner around the foot and leg or through some other custom fit system. But in spite of the lack of even a theory to support the premise of subtalar neutral as creating ideal biomechanical alignment of the bones of the foot and leg for skiing the premise seemed to be readily accepted as fact and quickly became mainstream. By the time The Shoe in Sport (which questioned the principles on which the plastic ski boot is based) was published in 1989 (1987 in German), neutral subtalar was firmly entrenched in the narrative of skiing.

In my US Patent 4,534,122 (filed on December 1, 2013) for a dorsal support system that I called the Dorthotic, I had unkowingly tried to fix the subtalar joint in a static position as evidenced by the excerpt below from the patent:

The system of the invention applies significant pressure to the dorsal (upper) surface of the foot over the instep, including the medial and lateral aspects thereof, and hence to the bones of the mid-foot to substantially prevent these bones from moving relative to each other.

Note: The prior art refers to the current paradigm in existence.

The objective of the dorsal support system was to immobilize the joints of the bones below the ankle in conjunction with the joints of the bones of the midfoot while allowing unrestricted dorsi-plantarflexion of the ankle joint within it’s normal range of motion. But the significant medial (inner) pressure applied by the  system to the bones of Podborski’s foot below his ankle made it difficult for him to stand and balance on one foot with the system in a ski boot shell even on the concrete floor of my workshop. Removing the offending structure from the dorsal support system quickly resolved the issue by allowing his foot to pronate. This made me aware that structures that impede supination did not appear to create issues. This insight raised the possibility of a fit system based on selective constraint applied to specific aspects of the foot and leg as opposed to what I termed indiscriminate (general) constraint.

Even though at the time that I wrote my US Patent No, 5,265,350 in February of 1992 I still did not comprehend the mechanism behind the claimed superior performance associated subtalar neutral, I knew enough to know that attempting to fix the subtalar joint in any configuration in a ski boot would interfere with, or even prevent, a skier from balancing on one foot.

Here is what I said in the patent:

The prior art refers to the importance of a “neutral sub-talar joint”. The sub-talar joint is a joint with rotational capability which underlies and supports the ankle joint.

………………….the prior art which teaches, in an indirect manner, that the ideal function for skiing will result from fixing the architecture of the foot in a position closely resembling that of bipedal function, thus preventing monopedal function (balance on one foot on the outside ski).

I later discovered that the above statement came close to the truth.

I also discussed the issue of subtalar neutral in my post NO NEUTRAL GROUND (2.) published on September 1, 2014. But I did not learn about the origins of subtatar neutral and especially the intense controversy surrounding it in professional circles until recently when I came across a discussion on Root and his subtalar neutral theory in an online podiatry forum.

The Origin of Subtalar Neutral

Merton’s Root’s subtalar joint neutral theory was first described in the textbooks, Biomechanical Examination of the Foot, Volume 1. – 1971 (Root, Orien, Weed and Hughes) and Normal and Abnormal Function of the Foot – 1977 (Root, Orien, Weed). The basic premise of Root’s subtalar neutral theory is that a neutral position of the subtalar joint (which Root defined as existing when the foot was neither supinated or pronated), is the ideal position of function in static (two-footed bipedal, erect) stance and in gait where the subtalar neutral theory posited that the foot was pronated in the first half of the stance phase then transitioned through neutral in mid stance to become supinated in the latter half of the stance phase.

Root’s paradigm proposes that the human foot functions ideally around the subtalar joint’s neutral position and that deviations from this ideal position are deformities.

What Root really said

Root and his associates never stated that the joints of the foot should be immobilized in subtalar neutral. The reference to static in subtalar neutral as the ideal position of function in static stance pertained to a subject standing in place in an erect bipedal stance on a flat, level, stable surface with the weight apportioned between the two feet. In this static stance the Root subtalar neutral theory posited that the subtalar joint should rest in neutral. Root and his associates never stated, implied or suggested that the joints of the foot should be configured and immobilized in subtalar neutral. Further, Root and his associates made no reference, of which I am aware, to the application of subtalar neutral to activities other than static stance and gait. Critrics have asserted that a subtalar neutral position in static stance is neither normal or ideal. In defining subtalar joint neutral as normal, Root’s theory implied the existence of abnormal pathologies in the feet of the majority of the world’s population.

The lack of evidence

Critics of Root and his associates “Eight Biophysical Criteria for Normalcy” claim the criteria was nothing more than hunches, that these conjectures were accepted as fact, when, in reality, there was no experimental data or research to support them and that the eight criteria were neither normal or ideal.

 The STJ neutral position problem

One of the early critics of Root and his associates was Kevin Kirby, DPM. He is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt College in Oakland, Ca.

Kirby observed a large error range in determining STJ neutral position on the same foot from one examiner to another. In unpublished studies done during his Biomechanics Fellowship at the California College of Podiatric Medicine, Kirby found that the Biomechanics Professors were +/- 2 degrees (a 4 degree spread) and the podiatry students were +/- 5 degrees (a 10 degree spread)  in determining STJ neutral position.

Subtalar neutral appears to be what amounts to a knife edge between pronation and supination where neutral is the border or transition point between the two states. Unless the subtalar neutral position can be precisely and consistently identified, it is impossible to know whether the subtalar joint is pronated or supinated.

The future of subtalar neutral in skiing

Too many times theories of how the human foot functions and therefore how mechanically inducted foot problems are treated have been presented as if they were facts. The dogmatic adherence that sometimes ensues from such an approach has frequently stifled the evolution of foot mechanics. This has been particularly apparent in the field of podiatry which has been dominated by the Root paradigm. (4.)

The long standing controversy and growing challenges mounted against the credibily of Root’s subtalar neutral theory has significant implications for the continued promotion of subtalar neutral in skiing as providing the strongest position of the bones of the foot and leg.

It may eventually be shown to be unfortunate that Root’s influential textbooks were published at a time when the ski industry was attempting to come to terms with the skier/boot interface issues associated with the new paradigm created by the rigid shell plastic ski boot.

In my next post, I will discuss what a ski boot should do for the user or perhaps, more a case of what a ski boot shouldn’t do.


  1. Root ML, Orien WP, Weed JH, RJ Hughes: Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971
  2. https://wp.me/p3vZhu-Bv
  3. Are Root Biomechanics Dying: Podiatry Today, March 27, 2009
  4. Foot biomechanics- emerging paradigms: Stephen F Albert, 4th Congress of the International Foot and Ankle Biomechanics (i-FAB) Community Busan, Korea. 8-11 April 2014

 

IS SHIFFRIN ON THE LEVEL?

By on the level, I am suggesting that Shiffrin may have a much lower zeppa-delta ramp angle than her competition.

Here are some screen shots from the March 18, 2018 Are Slalom where Shiffrin won by  1.58 seconds. She is on and off her edges in milliseconds as she just seems to pop from turn to turn – Total Domination From Shiffrin (1.)

Compare the angles of Shiffrin’s ankle, knee and hip in the photo below to those of her competition in the second and third photos below.

Notice how extended Shiffrin’s lower body is as she exits the rise line and enters the bottom of the turn in the photo below from a training session earlier in the year.

Extended in the Are Slalom.

Out of the start her knees and ankles are almost straight!

In my next post I will explain what I think is happening and why.


  1. https://youtu.be/gQu-LkyfsRQ?list=PLo6mlcgIm9mzWPBpeXnH2CpFOXrWhBiEB

ZEPPA-DELTA ANGLE EXTENDER

The problem associated with measuring boot board (zeppa) and/or binding (delta) ramp angle as individual components is that the resulting angle may not accurately reflect the actual angle between the plane of the base of the upper surface of the boot board and the base of the ski in the boot/binding/ski system. Boot boards of the same zeppa angle may not necessarily have the same zeppa angle with the base of the boot shell due to design and/or manufacturing variances.

A level inserted into a ski boot shell with the boot board in place can be difficult to read. With the liner in place, this is not a viable option. A better option is to extend the angle of the boot board up above the top of the shaft of the boot so it can be accurately and easily read.

A simple device for this purpose can be made for about $25 with basic hand tools and a few screws using 2 – 8 in (20 cm) x 12 in (30 cm) x 1/8 in (3 mm) thick steel carpenter’s squares.

Place the long arms of the squares over each other as shown in the photo below and clamp them securely together. Two-sided tape can be used to help secure the alignment. Then drill a hole  at one point on the vertical leg and screw the 2 squares together.

Check the parallelness of the 2 opposite arms on a level surface with a digital level. If good, secure the 2 levels together with a second screw. Then affix a section of 3/4 in (2 cm) x 3/4 in (2 cm) square or L-bar bar on the top of the extender to rest the level on.

To use the extender, place a boot shell on a hard, flat, level surface. If the surface is not level it should be leveled before the extender is used.

The photo below shows the extender being used to measure the zeppa angle of an old Salomon SX-90 shell. I didn’t have the electronic level for the photo. So I used a small torpedo level.

Insert the lower arm of the device into the shell as shown in the right hand image and place the lower arm firmly on the boot board. Place the level on the top arm and read the angle.

The photo below shows the same process as above. But in this example, the liner is in place. If an insole is in the liner, it should be flat with no arch form. I highlighted the square bar with pink to make it easily visible.

A check of the zeppa-delta angle of the boot-binding-ski system can be done by mounting the boot in the binding of the ski that is part of the system and clamping the ski to a flat surface with sufficient force to ensure the camber is removed and the running surface of the base is in full contact with the supporting surface. A strap wrapped over the front of the boot shell and under and around the supporting surface then tensioned will help ensure that the toe plate of the binding is loaded.

The Zeppa-Delta Angle Extender provides the user with a fast accurate way to know their total number. What’s yours?

 

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.