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.

2019 BRINGS NEW DIRECTION TO THE SKIER’S MANIFESTO

Best wishes for 2019 to the followers of The Skier’s Manifesto with a special welcome to new followers.

As a result of comments and suggestions made by some of my followers I have decided to rethink and reboot The Skier’s Manifesto and focus my efforts on providing information in a hierarchal, logical, sequential manner designed to build a knowledge base to assist skiers and racers in maximizing their potential.

For those who are unfamiliar with my background and objectives in skiing I default to the comments of the gifted scientist, Alex Sochaniwskyj, who I had the distinct privilege and pleasure of working with on my 1991 research project. In his letter in support of my nomination for a 1995 Science Award, Alex said:

During 1991 and 1992, I had the opportunity of working with David MacPhail in the realization and testing of conceptually innovative sports footwear. Design of this type requires, knowledge, understanding and experience in a combination of disciplines including anatomy, physiology, biomechanics, sports dynamics, physical mechanics and design. David MacPhail exhibited this unique combination throughout all aspects of the project, and continues to research and explore developments in: influences of footwear on the kinematics and kinetics of human movement; the design of athletic footwear; and the etiology, occurence, frequency and prevention of athletic injuries.

My relationship with David MacPhail began in 1991. As member of the Industrial Design team hired to refine, build and test prototype ski boots based on David’s original ideas, I was responsible for the development of an “on-hill” testing program. The objective of this program was to record and evaluate the biomechanical impact of the new boot design in a real dynamic environment, and then compare the results to the theoretical model. Unlike other (ski boot) designs, David’s theoretical described skiers’ biomechanics in a realistic, uncompromising, dynamic situation. 

The design and development strategies used by David MacPhail are very holistic in nature, placing the human system as the central and most critical component in the biomechanical system.

His intent is to maximize human performance and efficiency, while foremost preserving the well-being and safety of users and minimizing biomechanical processes.

I started this blog in May of 2013 for the purpose of renewing my dedication and commitment to the evolution of skiing as a science, one that maximizes the human performance and efficiency of skiers and racers, while foremost preserving their well-being and safety.

In the following months I will be reviewing, deleting, editing and reorganizing existing posts and writing new posts for the purpose of creating a set of guiding principles that will assist the reader in understanding issues related to human performance. As always, I stress the need for unbiased, objective research and studies designed to clarify and evolve the knowledge base in skiing.

Comments and suggestions from my followers are welcome and appreciated. I called my blog the Skier’s Manifesto because it is for skiers to contribute so all can learn. My role is to facilitate and encourage meaningful dialogue. Input from the readers of my blog helps guide my efforts.

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

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.