Skier Balance posts

THE MECHANICS + BIOMECHANICS OF PLATFORM ANGLE: PART 8

A soon to be published study (1.) recognizes that recent advances in sensor-technology allow the kinematics and kinetics of skiing to be monitored and data collected during training and actual competitions. The data will generate detailed information about the biomechanical factors related to success in competition and used to individualize training and skiing and equipment for each unique skier and, most important, motivate innovative scientific research for years to come.

 Individualize equipment for each unique skier

I fervently hope that this marks the beginning of the realization of a vision I had 30 years ago; one that resulted in the 1992 on snow studies using a unique instrumented research vehicle I designed with a biomedical engineer. This research vehicle allowed data to be acquired from skiers ranging from World Cup and Olympic champions to neophytes during actual ski maneuvers and meaningful metrics generated with which to assess performance. The objective of the study was to validate my hypothetical model of the mechanics, neurobiomechanics and physics of platform balance and the mechanism of skier CNS mediated dynamic stability. A validated model is essential for the interpretation of performance extrapolated from data. The intent of the subsequent patents was to provide a knowledge base to serve as a foundation for a science that would eventually enable individual skier optimization of every aspect of equipment and make skiing as easy and intuitive as walking for the masses.

A major source of inspiration and direction for my work and especially for my persistence came from the medical text-book The Shoe and Sport, in particular, Part 6 The Ski Boot.

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.

The modern ski boot must be designed from a functional point of view, i.e., the design must take into consideration the realities of functional anatomy (axes etc.).

It (the design) should not make compromises at the expense of other joints (length of shaft, flexibility and positioning).

It (the ski boot) must represent the ideal connecting link between man and ski (steering and feedback).

I am forever indebted to  Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland, Professor Dr. M. Pfeiffer of the Institute for the Athletic Science, University of Salzburg, Salzburg, Austria, Dr. med. H.W. Bar, Orthopedics-Sportsmedicine, member of GOTS, Murnau, West Germany and W Hauser and P. Schaff of the Technical Surveillance Association, Munich, West Germany and other pioneers who inspired my efforts and paved the way to the future of skiing.

In the words of W Hauser and P. Schaff:

In the future, ski boots will be designed rationally and according to the increasing requirements of the ski performance target groups.

I sincerely hope that the work of Supej Matej and H-C Holmberg (1.) ushers in the future of skiing.

The Platform Balance Solution

In previous posts I established that:

  • the axis of rotation of the foot and the ski (steering) resulting from rotation of the femur in the socket of its ball joint with the pelvis by what amounts to a muscle driven torque motor, occurs behind the center of the long running surface of the base of the ski.
  • the ball of the foot of a skier is located on the proximate center of the long running surface of the base of the ski.
  • edging and carving force require components of force with vectors aligned 180 and 90 degrees to the transverse aspect of the base plane of the outside ski.
  • the rotational or steering force (torque) is the source of the vector of the 180 degree force acting into the snow.
  • the point of application of the rotational cutting force when the axis of rotation of the ankle is oriented on the X-Y axis of the ski is mechanically ineffective. The monoplanar nature of the torque makes it less effective in terms of contributing to skier dynamic stability.
  • the effect of side-cut on platform angle mechanics must also be considered.

From a mechanical-neurobiomechanical perspective, the logical place to apply the center of force of the foot acting 90 degrees (or slightly less) to the transverse base plane is under the ball of the foot (i.e. the head of the first metatarsal).

After a thorough investigation and analysis of the forces associated with platform angle mechanics I reached the conclusion that given the robust structure and the degree of stability of the head of the first metatarsal and the fact that the 90 and 180 degree forces should be congruent it seemed logical to apply the force acting 180 degrees to the transverse base plane of the ski to the medial aspect of the head of the first metatarsal. The 1992 study was designed to confirm or disprove the validity of this conclusion.

The graphic below shows the application of the rotational (steering) force to the medial aspect of the head of the first metatarsal.The photo below shows the robust force transfer structures under and on the inner (media) aspect of the head of the first metatarsal. 

In my next post I will discuss the requirements of a ski boot necessary for the user to simultaneously apply plantar force to the platform and rotational force to the medial aspect of the head of the first metatarsal.


  1. Recent Kinematics and Kinetic Advances in Olympic Alpine Skiing: Pyeonchang and Beyond – Supej Matej and H-C Holmberg: Frontiers in Physiology

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 by 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.

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.

 

NABOSO: FIRST SKI TEST RESULTS

I finally got a chance to test Dr. Emily Splichal’s surface science small nerve stimulating NABOSO insoles (1.)

Naboso (meaning “barefoot” in Czech) is the first-ever small nerve proprioceptive material commercially available in the health and fitness industry. The skin on the bottom of the foot contains thousands of (small nerve) proprioceptors, which are sensitive to different stimuli including texture, vibration, skin stretch, deep …

As I typically do, I used a one on one test protocol with a NABOSO 1.5 insole in my left ski boot and my normal insole in my right boot. The results were nothing short of amazing. There was almost no difference in the feeling under the sole of my left (NABOSO) foot compared to the sole of my right (normal insole) foot. The NABOSO Effect (as I call it) in my left ski boot was nothing like the effect I experience in similar tests in my Xero Prios or Lems Primal 2 minimal shoes. You’re probably wondering why I was amazed if NABOSO was no better than my normal insoles. The fact that I felt little difference told me that something was seriously wrong with my ski boots.

The first thing I suspected was that there was too much ramp angle (aka zeppa) in the boot boards in my Head 335 World Cup boots. I can’t recall what the factory ramp angle. But I lowered the heel a lot and the reduced ramp angle seemed to work well compared to the original ramp angle. As a reference, the boot board zeppa angle in the Head RD boot is 4.0 according to Head literature. The zeppa in recreational ski boots can be as much as 7 degrees. Since 1978, I have known that too much boot board ramp angle can cause significant balance and ski control issues for skiers. But I had no way of accurately determining what the optimal zeppa angle should be. What appears to work well for one skier does not necessarily work for another skier. Zeppa is a crap shoot, a good guess, a lottery. A few skiers win the zeppa lottery. But most skiers lose. I decided that I had to find an accurate way to determine the optimal personal zeppa angle for skiers and especially racers.

Necessity is the mother of invention.

I had a need to know situation. In my next post I will describe the Dynamic Ramp Angle assessment  device that I designed and fabricated and the incredible results that happen when zeppa angle is in the optimal range and the NABOSO Effect kicks in. Prepare to be shocked by the results. I was. I am still in shock. If the results hold up, optimal boot board ramp angle will be a big miss for the ski industry.


  1. http://nabosotechnology.com

BEYOND BIOMECHANICS BY DR. EMILY SPLICHAL

The following post appeared on the Evidence Based Fitness Academy (EBFA) fitness blog on February 6, 2018 under the title Beyond Biomechanics | Addressing Foot Pain with Sensory Stimulation (1.).

I have reproduced the post with the kind permission of Dr. Emily Splichal under the title Beyond Biomechanics by Dr. Emily Splichal because her emphasis on the role of sensory stimulation of the plantar foot on foot, lower limb and function of the entire body has both direct application to and implications for, skiing.

I have a theory on what I call The NABOSO Effect that explains how I think NABOSO insoles improve dynamic stability in the biokinetic chain that I will discuss in a future post. I have been testing NABOSO 1.0 and 1.5 for months.


Beyond Biomechanics | Addressing Foot Pain with Sensory Stimulation – by Dr. Emily Splichal

I want you to picture a human foot.   Now picture a person standing barefoot, and then walking barefoot.   Do you see the foot striking the ground and flexing under impact, only to re-stabilize and push off just a few milliseconds later?

Often times when we think of human movement we can’t help but to be drawn to the thought of joints moving and muscles contracting.   Or in the case of foot function we are quick to consider the mechanics of flat feet, high arches, pronation and supination.   However when we delve deeper into the science of human movement there is more than meets the eye.

The Two Sides of Foot Function

When I teach on behalf of EBFA Global or speak to my patients I always emphasize that there are two sides to foot function (and dysfunction) – biomechanical and neuromuscular.    Now both play an important role in foot function which means that both must be appreciated – however to solely treat foot pain with just one belief system in mind is inherently flawed.

In most Podiatric Medical Schools we are taught foot function and foot pathology solely from a biomechanical perspective.

This means that every patient is tested for foot mobility and told to stand statically to determine arch height and foot type.   Based on this foot-focused biomechanical assessment and foot classification system the patient’s cause of injury and treatment protocol is determined.   Some of the favorite treatment recommendations include motion-controlled footwear and custom-posted orthotic both of which are prescribed with the hopes of controlling foot-focused biomechanics and thereby reducing their foot pain.

Beyond Biomechanics

The other side of foot function is one that is driven from a neuromuscular perspective and integrates the science of sensory stimulation and fascial systems.   In the case of neuromuscular function every patient would be assessed for sensitivity of plantar mechanoceptors as well as co-activation patterns between the foot and the core.  The role of minimal footwear, myofascial releasing, breathing patterns and compensation patterns more proximal would all be considered.

So which is more appropriate?  Well it depends.   In certain cases there will be a stronger argument towards a more biomechanical influence and in others it is more sensory.  This means it really is a marriage between the two approaches that provides the greatest patient outcome.

Sensory Stimulation in Foot Pain

My practice and Podiatry career is built around bringing an awareness to the important role sensory stimulation has on foot function and foot pain.

With every step we take impact forces are entering the foot as vibration.  This vibrational noise stimulates unique mechanoceptors on the bottom of the foot and is used to coordinate the loading of impact forces through coordinated contractions of the intrinsic (small) muscles of the bottom of the foot.   This co-contraction leads to a stiffening or strengthening response of the foot.

Researchers such as Nigg et al. and Robbins et al. have demonstrated a direct relationship between sensory stimulation of the plantar foot and intrinsic muscle strength concluding that one is necessary for the other.   This means that if our footwear or orthotics disconnect us from sensory stimulation – as in the case of cushioned footwear – this can actually weaken our foot making us susceptible to plantar fasciitis, Achilles tendinitis and stress fractures.

Beyond Vibration Stimulation

Vibration stimulation is an extremely important sensory stimulation that enters our foot however it isn’t the only stimulation.   Another important stimulation is the ability for our foot to determine texture and if a surface is rough or smooth.   This information is used to help maintain dynamic balance (think walking on ice).

Enter the merkel disk mechanoceptors.   These superficial sensory nerves are used to determine what’s called 2 point discrimination which is translated to roughness or the texture of a surface.  Surface texture and insole texture is one of the most studied aspects of foot stimulation and posture or gait.  From decreased medial lateral sway in patients with Parkinson’s or MS to reduced prefrontal cortical activity in atheltes post-concusion the applications are promising!

One area that hasn’t been focused on for sensory stimulation and foot function is foot pain.  I am here to change the awareness around this concept and share the powerful application of sensory stimulation and foot pain.

As we mentioned earlier sensory stimulation of the foot leads to a contraction of the intrinsic muscles of the foot.   Intrinsic muscle contraction is not only a criticial step in the damping of impact forces but has also been shown to increase the medial arch and build co-activation contractions in the core.

 The Evolution of Textured Insoles

In October 2017 Naboso Technology launched the first-ever commercially available textured insole!   Naboso Technology essentially brought the science of touch and years of textured insole research to the market place giving new hope to people with foot pain.

Available in two strengths – Naboso 1.0 (1mm texture) and Naboso 1.5 (1.5mm texture) Naboso Insoles are designed to be worn without socks (or at the most very thin socks).  They fit into all footwear, are freely movable in all planes of motion and are only 3mm thick.

FROM THE GROUND UP

Are you barefoot strong?


Learn more about the power of texture! – http://www.nabosostechnology.com

  1. https://barefootstrongblog.com/2018/02/06/beyond-biomechanics-addressing-foot-pain-with-sensory-stimulation/

 

THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: BALANCE PLATFORM MECHANICS

Turntable rotation generated by the powerful internal rotators of the pelvis (the gluteus medius and minimus) in combination with second rocker mechanics can create a platform under the body of the outside ski and foot that a skier can stand and balance on using the same processes to balance on solid ground. The associated mechanics creates a platform under the body of the outside ski by extending  ground reaction force acting along the portion of the inside edge in contact with the snow, out under the body of the ski.

In order to understand the mechanics, we need to start with a profile through the section of the body of the ski, binding and boot sole under the ball of the foot. The graphic below is a schematic representation of a ski with a 70 mm waist and 100 mm shovel and tail with an arbitrary length of 165 mm. The total stack or stand height from the base of the ski to the surface of the boot that supports the foot is 80 mm. The uppermost portion of the schematic shows the shell sidewalls of a 335 boot in relation to the 70 mm width of the stack. A ski with a 70 mm waist will place the center ball of the foot of skiers with US Men’s 10 to 12 feet close to over the inside edge. The heavy black line at the bottom of the stack shows the projection of the sidecut width beyond the waist.The schematic serves as a base on which to overlay a free body diagram showing the forces acting across the interface of the inside edge with the snow. This is where the rubber meets the road.

There are two possible scenarios in terms of the axis on which the center of pressure W of the skier will act. Unless the foot can sufficiently pronate and especially generate impulse second rocker loading, W will lie on the proximate anatomic center of the foot and transverse center of the body of the ski as shown in the graphic below. In this location, W will create a moment arm due to the offset with the GRF Pivot under the inside edge at the waist. The resulting moment of force will externally rotate the ski and foot under load out of the turn while simultaneously rotating the leg externally.The graphic below shows the second scenario where the center of pressure W lies directly over the GRF Pivot under the inside edge. In this position, W will load the inside edge under the ball of the foot and assist edge grip. But in this configuration, rotating the ski onto its inside edge necessitates overcoming the moment of force created by the moment arm resulting from the offset between the GRF Pivot and GRF acting at the limits of the sidecut. This requires a source of torque that acts to rotate the ski into the turn about the pivot acting at the inside edge at the waist of the ski.An obvious source of torque is to use the leg to apply force to the inner aspect of the shaft of the foot; aka knee angulation. But this will not create a platform under the body of the outside ski. Applying a load to the vertical wall of the shell opposite the ball of the foot will apply torque load to center at the GRF pivot as shown in the graphic below. The moment arm is formed by the point at which the Turntable Torque is applied to the boot sidewall (green arrow) to the center of rotation at the GRF Pivot.

 

The torque applied to the vertical sidewall of the boot shell is the Effort. The sidecut of the ski is the resistance. What effect will this have on the body of the ski under the foot? There is a lot more to this subject that I will begin to expand on in my next post.

THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: GLUTE POWER EDGE CONTROL

The New Year started off on a positive note with a great post on preventing sports injuries by Rick Merriam; Engaging Muscles (1.), a new YouTube video by LaGrandNeve (2.) on the importance of the feet in skiing and the long anticipated delivery of the CARV system.

In his post on preventing sports injuries, Merriam, cuts right to the heart of the matter when he states:

Sadly, most professional athletes don’t even know what it feels like to have muscles pulling at the right time.

Said another way, most professional athletes haven’t experienced what it feels like to perform with more stability throughout their chain.

By chain, Merriam is referring to the biokinetic chain.

My consistent finding over the years has been that most skiers, even racers at the World Cup level, don’t know what a stance founded on a strong, stable biokinetic chain should feel like. Even among those who have skied for decades, many have never experienced it. And the role of muscles is rarely, if ever, mentioned in discussions of ski technique or analysis of technique.

In Corso di sci Check Point 2018 – 03 (2.); Piedi cerca spigolo (Feet looking for corner) Valerio Malfatto states:

Contrary to what is believed in the curves with the skis the feet are very important we see how and why.

At about 1’50” into the video, Malfatta begins to draw a series of sketches. The first sketch appears to show how eversion of the foot puts the outside ski on edge by creating a flow of force into the turn. He appears to acknowledge how the ski and foot can either rotate to the outside of a turn (outside foot/ski inverts) or the inside of a turn (outside foot/ski everts). Then he appears to be showing how pressure applied under the ball of the outside foot rotates the ski onto it’s inside edge. Since I understand very little spoken Italian, it would be helpful if a follower of my blog who speaks Italian could post a comment explaining what Malfatto is saying in his video. My apologies to Malfatto if I have misinterpreted his graphics.

The graphic below is a screen shot from Malfatto’s video that shows how the foot and ski have rotated into the turn by pressure applied under the ball of the outside foot.

Although I have seen examples in that suggest rolling the ankles of the feet into a turn will apply edging forces, Malfatto’s video is the first example I have seen that appears to recognize that the outside foot and ski of a turn will tend to invert (rotate downhill) in the load phase under the force applied by the weight of the skier in the absence of a countering eversion torque.

While elite skiers and racers are usually aware of pressure felt under the ball of  the outside foot, it is difficult to replicate the feel in a static environment. So static exercises are often employed in an attempt to demonstrate what the skier is doing.

At about 5’30” into Malfatto’s video there is a dryland demonstration of the outside foot of a turn being rotated into the turn by contracting the muscles that evert the foot while the inside foot is rotated into the turn by contracting the muscles that invert the foot. There are a number of problems associated with attempting to hold skis on edge by contracting the inverter and everter muscles:

  • The muscles are in concentric contraction; i.e. they are physically shortening.
  • Both muscles are extensors of the ankle; i.e. as they shorten, they will plantarflex the ankle. This will shift the weight of the skier back under the heel, pushing the skier into the back seat.
  • The use of muscles to evert and invert the feet require conscious effort in what is called Executive Control. The processing rate of the brain in this mode is limited to about 60 bits per second compared to that of processing in Automaticity (subconscious control) which is about 11 million bits per second.
  • Both muscles are relatively weak compared to the glutes and soleus which are among the most powerful muscles in the human body.
  • Neither the everters or inverters cross the knee joint.

At the time that I wrote United States Patent 5,265,350 in February of 1992, I described the lack of knowledge of the complex biomechanics of the human muscle-skeletal system as it relates to the interaction of the foot with footwear such as skates and ski boots. In consideration of this, I made a concerted effort to provide as much information as possible to those knowledgeable in the field with the objective of advancing the state of knowledge on the subject. Since the writing of my patent my knowledge has evolved and continues to do so.

The following statements are excerpted from my patent.

The most important source of rotational power with which to apply torque to the footwear is the adductor/rotator muscle groups of the hip joint. In order to optimally link this capability to the footwear, there must be a mechanically stable and competent connection originating at the plantar processes of the foot and extending to the hip joint. Further, the balanced position of the skier’s centre of mass, relative to the ski edge, must be maintained during the application of both turning and edging forces applied to the ski. Monopedal function accommodates both these processes.

As a result of the studies done in 1991 with the research vehicle called the Birdcage, I had come to recognize the importance of a mechanically stable and (physically) competent connection extending from the plantar processes of the foot to the hip joint to facilitate the power of the glutes for balance and edge control.

Yet a further problem relates to the efficient transfer of torque from the lower leg and foot to the footwear. When the leg is rotated inwardly relative to the foot by muscular effort, a torsional load is applied to the foot. Present footwear does not adequately provide support or surfaces on and against which the wearer can transfer biomechanically generated forces such as torque to the footwear. Alternatively, the footwear presents sources of resistance which interfere with the movements necessary to initiate such transfer. It is desirable to provide for appropriate movement and such sources of resistance in order to increase the efficiency of this torque transfer and, in so doing, enhance the turning response of the ski.

Precise coupling of the foot to the footwear is possible because the foot, in weight bearing states, but especially in monopedal function, becomes structurally competent to exert forces in the horizontal plane relative to the sole of the footwear at the points of a triangle formed by the posterior aspect and oblique posterior angles of the heel, the head of the first metatarsal and the head of the fifth metatarsal. In terms of transferring horizontal torsional and vertical forces relative to the sole of the footwear, these points of the triangle become the principal points of contact with the bearing surfaces of the footwear.

A control point in the form of a counter set medial to the head of the first metatarsal is used in order to restrain the first metatarsal against medial movement, such as would occur when internal torsional force is applied to the foot.

In skiing, the mechanics of monopedal function provide a down force acting predominantly through the ball of the foot (which is normally almost centred directly over the ski edge). In concert with transverse (into the turn) torque (pronation) arising from weight bearing on the medial aspect of the foot which torque is stabilized by the obligatory internal rotation of the tibia, the combination of these forces results in control of the edge angle of the ski purely as a result of achieving a position of monopedal stance on the outside foot of the turn.

The edge angle can be either increased or decreased in monopedal function by increasing or decreasing the pressure made to bear on the medial aspect of the foot (turntable rotation) through the main contact points at the heel and ball of the foot via the mechanism of pronation. As medial pressure increases (by glute torque), horizontal torque (relative to the ski) increases through an obligatory increase in the intensity of internal rotation of the tibia. Thus, increasing medial pressure on the plantar aspect of the foot tends to render the edge-set more stable. The ski edge-set will not be lost until either the state of balance is broken or the skier relinquishes the state of monopedal function on the outside ski.

The skiers demonstrating the use of the feet to apply edging forces to the skis at 5’30” in the LaGrandNeve video (2.) clearly show the skiers engaging the second rocker by impulse loading the outside foot and ski and then rotating the outside leg into the turn as they exit the fall line and enter the load phase.

The graphic below shows the device I designed and constructed to train skiers and racers in the movement and muscle patterns required to enable the power of the glutes to be engaged to establish a balance platform under the outside ski and control edge angle as described in my post THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: CLOSED CHAIN OUTSIDE LEG ROTATION. Two forces acting together are required to to create the mechanics that rotate the outside ski on it’s inside edge into the turn.

  1. The center of the weight applied by must be under the ball of the foot and,
  2. Rotational force must be applied to the medial (inner) aspect of the ball of the foot in what I described as Rocker TurnTable Rotation (4.).

If the center of the weight of the body W lies on the anatomical center axis of the foot (under the heel), it will act to oppose turntable rotation applied to the foot by the glutes.

In my next post, I hope to have data from CARV showing the loading pattern that enables the use of Glute Power for edge control.


  1. https://www.engagingmuscles.com/2018/01/01/prevent-injuries/
  2. https://youtu.be/aAJSqzcxrS0
  3. https://wp.me/p3vZhu-2cC
  4. https://wp.me/p3vZhu-2bb