World Cup ski technique


Note to the reader

The post that follows was originally published on March 1, 2016. At the time that I wrote it, I was trying to identify the optimal net (total) ramp angle or NRA using fixed angle ramps. But I found the process to be inconclusive for reasons I give in my recent posts on the dynamic ramp assessment device. I am reposting this older post because many of the concepts expressed are even more relevant in view of the results seen with the dynamic ramp assessment device and boot boards altered to the same ramp angle identified in dynamic testing.


The foundation of a strong technique is a strong stance. But what makes a strong stance? The angle of the combined ramps of the binding and boot board or zeppa in relation to the base of the ski. If the net ramp angle weren’t important, binding and boot makers would make their products with no ramp. If ramp angle doesn’t make a difference, why bother? But not only does net ramp angle make a difference, it has a significant effect on stance.  Stance affects balance and muscle power, especially the ability of eccentric gastrocnemius-soleus complex muscle contraction to absorb shocks that would otherwise be transmitted up the leg to the knees and back. I discussed some of these issues in WHAT’S YOUR ANGLE? – : ‎

If there were a problem, and there is, the ski industry is all over the place especially when in comes to binding ramp. There doesn’t appear to be any industry standards and especially any continuity between products. Worse, most skiers assume that their ski boots are putting them in the optimal stance. Without a reference they have no way of knowing. The Stance Ramp can give them that reference especially when it comes to how much ramp is enough, how much ramp is too much and how much ramp is too little.

Note Added March 19, 2018 – Having a kinesthetic sense of a stance based on tensegrity gives a skier a valuable tool that when used in a structured process can help them assess the effect of zeppa-delta ramp angle and the constraint imposed on their feet and legs by the structures of a ski boot.

In 1978, when I was building boots for female racers with small feet, I noticed that they were skiing like they were wearing high heel shoes. When I started checking their bindings and boot board ramps, I found out why. Some had 10 or 12 degrees or more of net ramp angle. After I started doing stance training with racers on a ramped board I discovered through empirical experiments that about 3 degrees of ramp angle seemed to give skiers the strongest stance.

Note Added March 19, 2018 – It now appears as if 3 degrees is the upper limit of the zone of stability. This explains why skiers started to ski better when the net ramp angle approached 3 degrees.

I didn’t really understand why until much later. Was the process scientific? No, not at all. Do studies of this critical issue need to be done? Absolutely. If I figured out that ramp angle was a critical issue almost 40 years ago, why is it that no studies appear to have done in the intervening years to determine the affects of ramp angle and identity the optimal angle?

With input from skiers in different parts of the world over the past two years, I have narrowed the ideal ramp angle down to about 2.7 degrees. This seems to be something of a standard in World Cup. Through experiments over the past few months, I have found that changes of 0.1 degrees can make a significant and easily perceivable difference. Optimal ramp angle isn’t just critical for World Cup racers, it is critical for all skiers. The easiest way to convince yourself of the importance of optimal ramp angle is for you to experience the effects of ramp angle through experimentation. How? With a Stance Ramp set to a base reference angle of 2.5 degrees.

The Stance Ramp lets skiers stand in their ski stance (barefoot is best) on a flat, level, surface then assume the same stance on the Stance Ramp, compare the kinaesthetic sense and judge whether they feel stronger of weaker. The angle of the Stance Ramp can be predictably increased or decreased by inserting shims at either end between the ramp and the surface it is supported on. When the ramp angle that makes the stance feel the strongest is arrived at, it can compared to the ramp angle of the ski boot board by having one foot on the Stance Ramp and the other in the ski boot.

The best part? The Stance Ramp is easy and inexpensive to make with readily available materials. I made mine out of some scraps of plywood I had lying around. Here’s what the Stance Ramp I made looks like. You stand with one foot on either side of the stiffener in the center with your heels at the high end (left end in the photo below).


Here’s a top (plan) view. It is a good idea to check the surface the ramp will sit on to make sure it is very close to level.


Here’s the underside of the Stance Ramp showing the element at the rear that gives the ramp its 2.5 degree angle. The stiffener in the center is important to ensure the ramp doesn’t flex under your weight.


The sketch below is a basic plan for a Stance Ramp. The only critical details are the height or thickness of the element that lifts the rear aspect of the ramp to achieve and 2.5 degree angle (angle A) and the distance the lift element is placed from the front edge of the ramp. The stiffening element in the center of my ramp is 8 cm wide. The ramp has to be big enough to stand with the feet under the hips and long enough to accommodate the length of the feet.

Stance Ramp

An online right angle calculator such as the one at can be used to calculate the spacing of the lift element from the low end (front edge) of the ramp based on its thickness.

SR calculate

Once the optimal ramp angle is arrived at, the Stance Ramp can be used in combination with the ski boot shell to confirm that the boot board is at the same angle.


In my next post, I will discuss what I call the Resistive Shank Angle that is the base to build  a strong stance on.


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.



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.



When a World Cup racer wins a GS by a commanding margin, it’s a sure sign they’ve crossed the line and the gravity of the situation is significant. But I’m not talking about  breaking any rules. Instead, I’m referring to Hirscher and Shiffrin mobilizing the force of gravity by jumping across the rise line above the gate and/or minimizing pressure while rotating their skis across the rise line towards the gate so the edges of their outside ski progressively engage and lock up as they extend and incline closing the kinetic chain. Knee extension, in combination with ankle extension, uses the momentum of COM in conjunction with the force of gravity to progressively engage and apply force to the outside ski.

Reilly McGlashan has an excellent YouTube analysis of Marcel Hirscher using this technique in the 2017 Alta Badia GS (1.) The technique Hirscher and now Mikaela Shiffrin are using relates directly to the second rocker/internal rotation, impulse loading mechanism I described in a series of posts. The text below is excerpted from a comment I posted on McGlashan’s YouTube video analysis of Hirscher.

Hirscher progressively engages his edges, especially on his outside ski then hooks a tight arc close to the gate to establish his line. Once he has established his line, he no longer needs his outside ski. He gets off it in milliseconds and uses the rebound energy to project forward with only enough pressure on his uphill (new outside) ski to influence his trajectory of inertia so his COM enters the rise line at a low angle of intersection. He gets rebound energy from the loading  of his outside ski and from what amounts to a plyometric release of muscle tension from the biokinetic chain of muscles extending from the balls of his outside foot to his pelvis. The energy is created by the vertical drop from above the gate to below the gate similar to jumping off a box, landing and then making a plyometric rebound. Hirscher is skiing the optimal way and it shows on the clock and leader board.

Replicating the mechanism in a static environment is not possible because there is no inertia. But a device I have designed and constructed enables the mechanism to be rehearsed with the same feeling as in skiing.

The key is loading the forebody of the outside ski with a shovel down position as the leg is rotating the ski into the turn. This sets up the second rocker impulse loading mechanism that tips the ski onto its inside edge. Extending the knee and ankle uses momentum to exert a force on the snow with the ski.

The photo below shows the training mechanism head on. The white horizontal arms represent the sidecut of the ski. The platform under the foot can be adjusted transversely to change the sensitivity. Vertical plates set beside the ball of the foot and on the outer corner and behind the heel transfer turntable rotation torque to the ski created by rotating the leg internally with the glutes. The platform will only tilt under impulse loading if the second rocker can engage. Few skiers can use this mechanism because their ski boots do not accommodate second rocker biomechanics.

The link below is to a video that shows the effect of extending the knee and ankle while moving the hips forward and over the support foot (monopedal function). The stack height and minimum profile width of are FIS 93 mm/63 mm. Rotation in itself will not cause the device to tip onto its inside edge if centre of pressure is on the anatomic centre of the foot (through the centre of the heel and ball of the second toe).

Dr. Emily Splichal’s recent webinar on the Science of Sensory Sequencing and Afferent Stimulation (2.) is relevant to motor control and cognitive development associated with high performance skiing. Pay careful attention to Dr. Splichal’s discussion of the role of mechanoceptors and the fact there are none on the inner (medial) aspect of the arches of the feet which is why footbeds or anything that impinges on the inner arch is a bad thing. I will discuss the implications of Dr. Splichal’s webinar in a future post.

In my next post, I will provide detailed information on the training device.





Since I started this blog with my first post, A CINDERELLA STORY: THE ‘MYTH’ OF THE PERFECT FIT (1.) on 2013-05-11, THE SHOCKING TRUTH ABOUT POWER STRAPS (2.) is by far the most widely viewed post. This is significant because the content of this post challenges premises that are widely embraced and cited as knowledge that is fundamental to skiing.

The greatest enemy of knowledge is not ignorance; it is the illusion of knowledge.

                                                                                    – attributed to Stephen Hawking

Widely accepted false beliefs can negate incentives to pursue the acquisition of knowledge necessary to understand complex issues that fall outside the limits of established paradigms. A prime example being the ability to balance perfectly on the outside ski.

Observing great skiers like Marc Giardelli or Ingemar and more recently, Mikaela Shiffrin, Lindsey Vonn and Marcel Hirscher balance perfectly on their outside ski suggests it is possible. But uninformed observation in itself does not impart, let alone lead to, an understanding of the associated mechanics, biomechanics and physics of perfect balance on the outside ski as it equates with neuromuscular mediated dynamic balance of triplanar torques acting across the joints of the ankle/foot complex, knee and hip. The intrinsic need of those who regarded as authorities on ski technique to provide plausible explanations for the actions of elite skiers led to the fabrication of terms such as knee angulation that served to create an illusion of knowledge of the mechanism of balance on the outside ski. Knee angulation also provided an effective mechanism with which to demonstrate the mechanics of edge hold.

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

                                                                                                                          – Albert Einstein

While knee angulation provides a plausible explanation for a mechanism with which to rotate a ski onto it’s edge, it does not explain the mechanism of perfect balance on the outside ski in accordance with Newton’s Laws and the principles of functional anatomy. Solving this mystery required raising new possibilities and creating a new paradigm; one that looked at the function of the human lower limbs from a new perspective with new possibilities.

It took me from 1980 to 1990 to discover how the mechanism of balance on the outside ski works. Trying to impart an understanding of this mechanism to others has presented significant challenges because the illusion of knowledge within the ranks of the ski industry has resulted in a hardened mental model that makes the real mechanism all but invisible. The resulting information bias causes people to seek information that supports what they believe while filtering out information that conflicts with what they believe; i.e.

I don’t need new information on how to balance perfectly on my outside ski because I have been doing this for years and I don’t need to know anything more.

But the reality is, that with rare exception, while elite skiers and even World Cup racers may think they can balance on their outside ski they have no way of recognizing the correct feeling, let alone confirming that they are actually doing what they think they are doing.

I have designed and fabricated a device with which to train skiers/racers to create a platform under their outside ski on which to stand and balance perfectly on. The device can be used to capture what I call a skier’s personal Balance Signature using technologies like CARV. More on this in my next post.



One of the most important events in the turn sequence is edge change. Yet, it is rarely mentioned in technical discussions. One of the few references I was able to find on edge change is in the CSIA Technical Reference which states:

Edge Change = Balance Change: Changing edges requires a change of balance.

Edge change occurs during an unbalanced, controlled fall in the transition phase that leads to the development of a balanced position on the outside ski as it crosses the fall line in the bottom of a turn. Properly executed, edge change leads to the development of a platform under the outside ski for the skier to stand and balance on.

The edge change sequence starts in the transition phase when a skier begins to transfer weight from the outside (downhill) ski to the inside (uphill ski). At the start of the transition, the edges of the inside ski are uphill and on the lateral (little toe) side of the foot. From a perspective of the gait cycle, the base of the ski is inverted (turned inward towards the center of the body). This is the normal configuration when the foot is unweighted in the gait cycle. The foot strikes the ground on the lateral (little toe) side and rotates about it’s long axis in the direction of eversion to bring the three points of the tripod of the foot into contact with the ground. As the foot everts, the leg rotates internally through torque coupling in the subtalar joint. The normal kinetic flow from foot strike to the support phase in mid to late stance is one of inversion of the foot/external rotation of the leg to eversion of the foot/internal rotation of the leg. Put another way, the human lower limbs will naturally rotate into a turn so long as the biomechanics are not interfered with.

At the start of the transition leading up to ski flat between edge change, the center of pressure (COP) of the weight of the body applied by the sole of the inside foot will be under the heel where it is aligned on the proximate center of the ski.

The Eversion/Internal Rotation Cascade

Transferring the weight from the outside foot and ski to the inside foot and ski in the transition phase sets in motion what I call the  Eversion/Internal Rotation Cascade. When the cascade starts, the force F W applied to the ski by the foot  by the weight of the body will impart rotational inertia as the ski rotates about the pivot point formed by its inside edge.

For the sake of simplicity, the stack of equipment between the sole of the skier’s foot and the snow is represented by a rectangle in a 3:2 ratio where the stand height is 50% higher than the width (FIS maximum stand height = 93 mm – maximum profile width = 63 mm). Sidecut is also not shown.

The following graphics show the sequence of the Eversion Cascade. Note: Internal rotation of the leg is not shown in this sequence.

The first graphic below shows the moment or torque arm ma that is set up by the offset that exists between GRF from the firm piste acting at the inside edge and the point where the center of pressure of the weight of the body acts in the plane of the base of the ski. The large red arc shows the radius of rotation. The small red arc shows the radius of the moment of force. In this sequence, the ski is rotating downhill away from the pivot at the uphill edge.

When the base of the ski comes into full contact with the surface of the snow, rotational inertia, will make it want to continue rotating about the uphill edge and penetrate into the snow surface on the downhill aspect. If the force FW applied by the weight of the body is still aligned on the transverse center of the ski, it will oppose edge change.

In my next post I will discuss how the Second Rocker affects the mechanics of edge change at ski flat.



A recently published study on foot pressure data acquired during skiing (1.) recognized that compressive force pressure data acquired in skiing is underestimated by 21% to 54% compared to pressure data acquired on a force platform in a controlled environment.  The underestimation varies depending on the phase of the turn, the skier’s skill level, the pitch of the slope and the skiing mode. The paper states that other studies have stated that this underestimation originates from a significant part of the force actually being transferred through the ski boot’s cuff (to the ski). As a result, the CoP trajectory also tends to be underestimated along both the anterior-posterior (A-P) and medial-lateral (M-L) axes compared to force platforms.

In conclusion, these studies have highlighted a major contribution of different factors to the nGRF applied throughout a turn, such as the foot’s position during a turn (inside vs. outside), the CoP A-P (front to back) displacement, or precise loading of different foot sole regions.  Unfortunately, these results have been studied separately.

There is a lack of continuity across the various positions in skiing and, in particular, a lack of a model with which to explain mechanisms such as balance on the outside ski and open and closed chain internal rotation of the leg and foot in conjunction with progressive inclination and G force loading on it as the skier crosses the fall line in the bottom of a turn. The associated mechanics and biomechanics represent a new paradigm requiring new thinking and new insights. Existing text-book explanations are not sufficient to explain these mechanisms.

Open Chain Whole Leg Rotation vs. Closed Chain Rotation

Rotation of an unloaded (non-weight bearing) lower limb is relatively straight forward when there is a small angle at the knee. As resistance to rotation of the foot is progressively introduced with increasing weight imposed on it, the kinetic chain begins to close. As it closes, the points at which the foot transfers torque to the walls of rigid shell footwear such as ice skates and ski boots starts to emerge as an issue as does the loading of the foot created by the weight of the body imposed on it and the position of COM in relation to the foot.

In order to tension the biokinetic chain and trigger the two-phase Second Rocker, COM must be aligned over the foot as shown in the grahic below.  This alignment requires that the leg adduct (move towards the center of the body) approximately 6.5 degrees. To bring the 3 points of the tripod of the foot into contact with the ground, the foot must evert (sole turn outward) the same amount. Eversion is accompanied by a corresponding torque coupled 6.5 degrees of internal rotation of the leg as shown in the left hand figure in the graphic below (see my post – OUTSIDE SKI BALANCE BASICS: STEP-BY-STEP). The bipedal figure on the right shows adduction, eversion and internal rotation as 0.0 – 0.0 – 0.0 for reference. The monopedal figure on the left shows the changes in adduction, eversion and internal rotation as 6.5 – 6.5 – 6.5.


The alignment of COM with the foot can be achieved by moving COM laterally as shown by the arrow emanating from COM in the Monopedal figure or by moving the foot medially as shown by the white arrow or through a combination of the two movements.  The act of positioning COM over the outside foot (Getting Over It), sets in motion internal rotation of the outside leg and eversion of foot into the turn. This engages an over-centre mechanism between the platform of the ski and the inside edge underfoot.

The over-centre mechanism results in an alignment of the resultant force R forming an angle with the transverse aspect of base of the ski that is slightly less than 90 degrees. In order to Get (COM) Over It (the foot), it is essential that the outside leg is not only able to adduct and rotate internally as the foot everts, but to achieve this configuration without delay in order to set up the over-center mechanism. The problem for the majority of skiers is that the objective of most boot fit systems and boot-fitting procedures is to support the foot in a neutral configuration. Eversion of the foot is a component of pronation. Impeding or preventing pronation, restricts or even prevents the required amount of eversion.

Closing the Kinetic Chain on Whole Leg Rotation

Open kinetic chain leg/foot rotation with the foot unloaded (not bearing weight) is relatively simple. But the mechanics and biomechanics begin to get complicated when resistance is progressively introduced that starts to close the kinetic chain as happens when the outside ski is rotated across the path of the skier in the fall line in the bottom of a turn.
The graphic below shows a foot supported on a platform with 2 points of resistance (FR) applied to the platform opposite the 2 points of application of the moments of force, ML (green) and MM (red). The forces tangent to the arc of the moments of rotation are shown as FT.
When the weight of the body is progressively shifted to one foot (i.e. Monopedal Stance) and the foot everts, the talus (shown in gray in the graphic above) moves inward towards the center of the body and shifts slightly rearward as evidenced by the corresponding movement of the inside ankle bone.  This is easily seen when moving from bipedal to monopedal stance on a hard, flat surface while barefoot. In order to effectively transfer torque from the foot to the platform, the forefoot and ankle and knee joints must be fascially tensioned. This requires that the big toe (Hallux) be aligned on the anatomical axis (dashed line) and the forefoot fully splayed. This stabilizes the heel and head of the 1st metatarsal (ball of the foot).  Torque from internal rotation of the leg will be transferred to two discrete points adjacent the Load Counters mounted on the resistance platform.

Removing the resistance force FR from the inner (big toe) aspect of the platform provides insights to what I refer to as the Turntable Effect that is associated with internal rotation of the leg and eversion of the foot that creates an over-center mechanism. The turntable rotation is shown in light yellow. The effect will vary for different structures of the foot depending on the location of the center of rotation of the platform under the foot.

The location of the blade of an ice skate on the anatomical center of the foot has been used to explain why it is easier to cut into a hard ice surface with a skate compared to the edges of a ski. But the real reason it is easier is because ice skaters use the Second Rocker, Over-Center, Turn Table Mechanisms as shown in the graphic below. The skate is positioned under COM. It can be readily seen that the skater is not using the inner aspect of the shaft of the skate to hold the skate on edge.

In my next post, I will discuss the progress of emerging CARV and NABOSO technologies after which I will continue with my discussion of the Mechanics of Balance on the Outside Ski.

  1. Influence of slope steepness, foot position and turn phase on plantar pressure distribution during giant slalom alpine ski racing: Published: May 4, 2017  – Thomas Falda-Buscaiot, Frédérique Hintzy, Patrice Rougier, Patrick Lacouture, Nicolas Coulmy