In order to maintain the continuity of the ongoing discussion of Ligety’s Moment of Truth, I have changed the title of the series of posts on ROLL OVER to LIGETY’S ROLL OVER EXPLAINED. Although Roll Over is not exclusive to Ligety’s technique, the association will enable search engines to find and link the two series of posts.
In a series of posts, starting after this one, I am going to describe the mechanism of what I call Roll Over. This next series of posts will be the culmination of a series of posts on the mechanics, biomechanics and physics of Ted Ligety’s technique that started on February 19, 2014 with a post called LIGETY’S MOMENT OF TRUTH – STEP 1. The last post called LIGETY’S MOMENT OF TRUTH – STEP 5 – LIGETY STEPS UP THE PRESSURE was made on March 3, 2014. I first described the basic mechanism that I later called Roll Over in US Patent No. 5,25,350 published on February 3, 1993.
The difficulty in finding an easy way to communicate this action is the reason I did not take the LIGETY’S MOMENT OF TRUTH posts to a conclusion after the last post on March 3, 2014. In order to make Roll Over easier to appreciate and understand, I have designed a device that will enable a user to experience the feel of the events that are set in motion when the new outside ski changes edges and translates the foot towards the inside of the new turn as it everts the foot. As a preface to my explanation of Roll Over, I have provided excerpts below from my five posts on LIGETY’S MOMENT OF TRUTH. In order to acquire a complete understanding of the events surrounding Roll Over, the full content of all 5 posts should be read. If for some reason the links to the full posts don’t work, please copy and paste them into your browser.
LIGETY’S MOMENT OF TRUTH – STEP 1
If indeed no other skier in the world carves the way Ligety does then I say everyone else is skidding, not really carving at all. If Ligety is carving the right way, and we want to ski like him, we need to know what he is doing and why he is doing what he does. Stepping on the uphill ski in the transition when it is still on its uphill edge is the first step towards better carving. If it were that simple, everyone would be skiing like Ligety within 5 minutes of viewing the NY Times video. But what Ligety is doing is anything but simple. Stepping on the uphill ski is just the first step. Several more steps are needed before Ligety gets to the point that I like to call The Moment of Truth.
LIGETY’S MOMENT OF TRUTH – STEP 2
Given that Ligety’s inside turn (left) foot is ahead of his outside turn (right) foot and the angle of the left boot shaft is controlling the angle of flexion of his ankle, Ligety’s Centre or Pressure on his left foot will be under the heel and on the proximate centre line of the ski. It will stay there until his foot is flat or (i.e. – plantigrade) on the snow surface. It is at this point that what I refer to as the Moment of Truth occurs. The animation in the NY Times video got the part right that shows pressure (Centre of Pressure) acting on the proximate transverse centre line of Ligety’s left foot. What the NY Times didn’t show, and what is the most critical part of Ligety and Shiffrin’s technique, is what happens (or should happen) in the very brief interval during which Ligety’s foot is flat on the snow surface between edge changes and, thanks to Newton’s Laws, he is standing at a right angle to the slope. The NY Times also did not show the geometry of Ligety’s GS ski and its relationship with the key mechanical references of the foot. Twenty-seven years ago, in 1987, Professor Dr. M. Pfeiffer at The Institute for Athletic Sciences at the University of Salzburg in Salzburg, Austria said, “Correct positioning of the foot is more important than forced constraint and “squeezing” the foot. Pfeiffer also said, “If muscle function is inhibited in the ankle area (which is the role of the modern form-fitted ski boot), greater loads will be placed on the knee”. It appears that Dr. Pfeiffer’s words fell on deaf ears.
“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.
“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 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. (COMMENT – These biomechanics can only be set up when the new outside ski of a turn is flat on the snow surface).
LIGETY’S MOMENT OF TRUTH – STEP 3
LIGETY’S MOMENT OF TRUTH – STEP 4
In order to be able to develop a dynamically stable base of support on the outside ski of a turn, one that supports the processes that use external forces to drive the ski into the turn, the ski must have a waist that is close to the centre-to-centre dimension ‘X’ between the balls of the great and 2nd toes. In addition, the anatomical centreline of skier’s foot must be aligned with the running centre of the ski. The graphic below shows what it looks like when the foot is correctly positioned on a ski with the appropriate width underfoot. In reality, there is a stack of equipment between the sole of the skier’s foot and the snow surface. F.I.S. rules allow up to 100 mm of stack height between the sole of a racer’s foot and the snow surface. So the graphic below does not reflect reality. The reason I am starting with the skier’s foot directly on the ski top plate is to demonstrate that an applied vertical force acting against an opposing snow reaction force (SRF) is insufficient to explain the edging mechanics that skiers like Ligety and Shiffrin are able to develop. There are other factors at play that I will introduce in future posts.
US Patent No 5,265,350 – MacPhail: November 30, 1993 – “The prior art refers to the importance of a “neutral sub-talar joint”. The sub-talar joint is a joint with rotational capability which underlies and supports the ankle joint. The sub-talar joint is substantially “neutral” in bipedal function. That is to say that the foot is neither rolled inward or rolled outward. If the foot can be substantially maintained in a neutral position with the arch supported and with a broad area of the inner aspect of the foot well padded, there will exist a good degree of comfort. Such a state of comfort exists because the foot is not able to roll inward (pronate) to a degree where significant mechanical forces can be set up which would allow it to bear against the inner surface of the boot shell. In effect, this means that initiation of the transition from a state of bipedal to a state of monopedal function, is prevented. This transition would normally be precipitated by an attempt to balance on one foot. If the foot is contained in a neutral position, traditional supportive footbeds (arch supports) are quite compatible with the mechanisms and philosophies of the prior art.”
Here is what the inside and outside feet of a skier in a turn look like when the feet are in neutral.
LIGETY’S MOMENT OF TRUTH – STEP 5 – LIGETY STEPS UP THE PRESSURE
Since there are offsets or moment arm between CoP and SRF on each foot, the sole of the inside foot of the turn will tend to roll away from the centreline between the feet (i.e., it will tend to evert) while the sole of the outside foot of the turn will tend to roll towards the centreline between the feet (i.e., it will tend to invert). Under specific conditions the external forces acting on the skier will tend to make the outside foot of the turn rotate into the turn (ergo, it will tend to evert). But, for reasons that will be provided in a future post it is not possible to create conditions under which the external forces acting on the skier will tend to make the inside foot of the turn rotate into the turn. For this reason the force applied to the snow by the skier must be directed to the inside edge of the outside ski of the turn. The inside foot and leg are used to help direct the force to the outside ski. This what Ligety and Shiffrin do so well.
Here is a step by step photo sequence that shows these movements.
Frame 1 – This is the point just before Ligety begins to step on the current edge of the inside ski. Due the offset between the pressure applied on the centre of Ligety’s inside ski and its inside edge his ski is tending to rotate out of the turn. This force is opposed by the action of Ligety’s left thigh which is using his leg like a lever to press against the uphill aspect of the cuff of his ski boot.
Frame 2 – Ligety has started to step on the uphill ski while it is still on his current edge. As he extends his inside leg, he releases the pressure on his outside ski and the muscle force in his thigh that has been controlling the edge angle of his inside ski. The pressure under the heel of Ligety’s left foot starts his ski rotating out of the turn. From a biomechanical perspective, his left foot is ‘seeking 3-point ground contact’.
Frame 3 – As Ligety continues to progressively extend his left leg, he is simultaneously moving forward in the hips, something most racers fail to do.
Frame 4 – Ligety’s foot has flattened on the snow and his Centre of Mass is stacked on top of it. This is the point where the edge change occurs. Ligety will transition from the inside edge of his old inside ski to the inside edge of his new outside ski. This point marks the end of the transition phase and the start of the new turn. What happens next is critical. Depending on what he does next, the forces will either rotate Ligety’s out of the turn or into the turn. Since they are actually moments of force or torques, I call this point the Moment of Truth. It was at this point that the NY Times video: Ligety on GS, showed the pressure Ligety is applying on the proximate centre of his ski.
Frame 5 – If the pressure Ligety is applying stays under his heel or even on the centre line of his ski it will cause his ski to rotate out of the turn.
Frame 6 – The tendency of Ligety’s ski to rotate out of the turn will depend on the magnitude of forces opposing this movement. The only option Ligety or any skier has to counter the tendency of the external forces acting on him to cause the outside ski to slip is to increase the edge angle, usually by increasing the angle of inclination. The problem with this option is that a point of diminishing returns is reached where further inclination has the opposite of the intended effect.
At the point where Ligety’s ski flattens on the snow between edge changes there are two options in terms of which side of the inside edge of the ski the pressure applied by Ligety will end up. Put another way, there are two possible moment of force outcomes. Given the vagaries of human nature, there will be those who will take the position that each option offers advantages. Because of this they are, in effect, equal. In fact, I have already had this argument put to me. This is like positing that walking sideways or backwards, or crawling on all fours is equal to doing what we are designed to naturally do, walking forward using alternating single limb support. Being unstable and therefor unbalanced on 2 feet, is not the same as, let alone superior to, being dynamically balanced on a base of support on one foot. In my next post I will explain why racers like Ligety and Shiffrin prefer the latter option.
The reality is that neither Ligety or Shiffrin appear to be making any attempt to keep their unique techniques a secret. To the contrary, of all the racers on the World Cup circuit, no one has been more open and forthcoming about their techniques than Ted Ligety and Mikaela Shiffrin.
In a series of Burke Mountain Academy YouTube videos posted in the summer of 2014, Shiffrin narrates a series of drills that she uses to hone her technique. She continues to comment on her technique in videos on a regular basis. Still, views of Burke videos are 5,000 to 10,000 compared to 500,000 to a million views for videos that advocate using the legs like 2″ x 4″s to hold both skis on edge to make pure carved turns.(https://www.youtube.com/user/burkemtnacademy)
In the New York Times video, ‘On Giant Slalom: Ted Ligety’ (http://www.nytimes.com/video/sports/olympics/100000002705897/on-giant-slalom-ted-ligety.html), the commentator states that for 8 years Ligety has been perfecting a new style of turning. As someone who is passionate about skiing and committed to advancing the sport as a science, that statement instantly got my attention. The commentator goes on to say, “the most noticeable element of Ligety’s style is seen mid turn where his body is horizontal to the hill”. The narrative on the video states, “Ligety’s path is smoother than that of his foes, who ski in violent fits and starts, making adjustments that spray snow”. Ligety, “I’m starting my turn earlier (while its still on its uphill edge) and finishing it later than the other guys”. The clean, low profile snow pattern off Ligety’s outside ski tells the story. The edges are slicing a clean path into the snow with no sideslipping.
Says Ligety, “I always been known for my big edge angles even on the old skis”. The angle of Ligety’s outside ski is shown in the NY Times video. I measured it at approximately 80 degrees to the snow surface.
The NY Times video compares Ligety to Bode Miller at the same point in a turn. Miller is spraying a large amount of snow off his outside ski, Ligety? Almost none.
Obviously, Ligety is putting very different forces on his outside ski than Miller. But in what way? And how is it that Ligety is able to make the edges of his outside ski hold at such extreme angles? That’s a question I put to members of a FaceBook group for serious skiers and ski professionals and coaches.
When force is applied to the outside with the base at an angler greater than 45 degrees to the snow, the component of sheer force that makes the edge slip is greater than the component of vertical force that makes the edge grip. Since as far as I know, Ted Ligety is bound by the immutable laws of the universe, there has to be a logical explanation for why he appears to be defying the laws of physics. Cracking the Ligety Code holds the promise to make skiing better for all skiers, not just World Cup racers. But interest from the members of the FaceBook group from those who should be motivated was the equivalent of a yawn and a “Why bother?”. The explanations from those who did respond were surprising, but not shocking, “It’s magic”, “Ligety is different” or “This is a dumb question”.
Although some critical issues are left out of their discussions, probably because Shiffrin and Ligety are not aware of these omissions, the superiority of their techniques, as evidenced by visits to the podium should serve as the impetus for those who are in the ski teaching and coaching professions to put Ligety and Shiffrin under a microscope, analyze their movements and integrate them into ski teaching methodologies and coaching world wide. The main reason this isn’t happening appears to be that those who should be motivated aren’t or, perhaps just not interested in putting in the effort. This group represents an influential camp that’s slowing killing skiing by discouraging the development and analysis of ski technique based on sound principles of science. Instead, they default to the scripted narrative that every skier and every country is different, that there are an unlimited number of ways to ski and that no one way is better than another. Every country has its own unique technique and they all work yada, yada, yada.
Ted and Mikaela don’t have secret techniques. They are ‘just different’.
Here’s a highly edited video clip of Ligety that I created to show how Ted uses Roll Over.
The technique of the world’s best skier has always been about torsion, not simple leverage.
Watch carefully how Ligety starts to apply rotation to his uphill as soon as he starts the transition phase. As Ted crosses the fall line, his inclination reaches a point where the inside edge locks up with the snow and the shovel engages creating what I call a ‘comma hook’ that redirects his line while loading his outside ski like a springboard. The actual ‘loaded turn phase’ is a mere fraction of second after which Ligety is into the transition phase, off the edge of his old outside ski and accelerating forward towards the next gate. Anyone who thinks they can beat Ted or any racer using this technique with a pure carved turn needs to see a really good therapist.
Ligety’s use of Roll Over and torsion explains how he can reach extreme edge angles on his outside ski.
Numerous studies have attempted to find a correlation between foot size and height. I believe there is a reasonable correlation between foot size and height if stature is considered. Ski racers tend to have moderate body masses. When I worked on racer’s boots, most female racers had a US ladies size 7 foot (US men’s 6). Male racers tended to have a US 8 or 9 foot size. Ski boot makers usually make prototypes in a US men’s size 9 then scale the shell up or down to create other sizes.
Lange recently introduced a size 4 US men’s race shell. Perhaps it is more accurate to state that Lange reintroduced a size 4 race shell. After I learned how to read the shell mold codes forty years ago, I knew that Lange made size 4 shells. However, they only sold them in softer children’s boots in North America. The XLR Race boot was only sold in Japan. After I got the Canadian distributor to bring in a supply of size 4 XLR Race boots, I was inundated with calls from all over Canada from female racers with small feet who heard that a size 4 XLR was available.
In my experience, I was usually able to estimate the size of a racer’s foot by looking at their stature and height. Here is a list of 6 top World Cup racers in order of height.
Ted Ligety 1.80 m
Lindsey Vonn 1.78 m
Marcel Hirscher 1.73 m
Tina Maze 1.72 m
Mikaela Shiffrin 1.70 m
Anna Fenninger 1.66 m
Based on Lindsey Vonn’s stature, I estimate that she has bigger feet than both Tina Maze and Mikaela Shiffrin who are very close to the same height. Vonn is close to the height of Ted Ligety. I estimate that she has at least a US ladies Size 8 to 8.5 while Ted Ligety’s foot is in the order of a US men’s 9. Anna Fenninger is 1.66 m and small boned. She probably has small feet, smaller than Shiffrin who probably has a size 7 ladies (6 men’s). Anna Fenninger’s foot will be no bigger than a size 6 ladies (US men’s size 5). Marcel Hirscher at 1.73 m probably has a size 7.5 to 8 US men’s foot.
With a ski that is 65 mm in Minimum Profile Width who has the winning feet? Ted Ligety and Lindsey Vonn.
Now that the 2012-2015 World Cup season is underway, I plan to start interspersing analyses of the technique of racers such as Ligety, Maze, Vonn, Shiffrin, Hosp and Velez Zuzzuolva. There is an emerging trend towards the extension-pendulum effect technique that is the signature of Ligety and Shiffrin.
After indicating before the start of the season that she would make her debut in World Cup Super-G this year, Shiffrin recently announced that she would not compete in the Super-G in Val d’sere next week but would instead focus on GS. This came after Shiffrin’s worst drought since her the first of her 10 World Cup victories two years ago. I suspect that Shiffrin’s difficulties can be attributed to a change in some aspect of her equipment, most likely her boots. She looked much closer to her usual form in Are last Saturday. If the source of her problems was, in fact, in her boots and this has been corrected, I am confident that she will regain her form in the new year. Focussing on GS is a smart move by Shiffrin. If Shiffrin can dominate in GS she has an excellent chance of winning in Super-G.
One of the challenges in analyzing technique using video clips is that the camera angles and image quality are typically far from ideal. In addition, cameras often switch at key moments in a sequence, usually part way through the transition phase that starts at the end of a turn. Finding a sequence that illustrates the mechanics, biomechanics and physics of skiing can take hours of frame by frame analysis followed by additional hours of work annotating and animating the key images. More interesting than the racers who are very close to getting every aspect of a technique right are those who make the essentially the right moves at initiation only to have to resort to survival tactics usually due to interference from their ski boots.
Since extension is a hot topic on the internet, mainly due to Ligety’s very effective use of it, extension will be the subject of my next post.
An interesting trend is emerging in World Cup Alpine competition. The movement pattern of some male racers is starting to resemble that of Ted Ligety while the movement pattern of some female racers is starting to resemble that of Mikaela Shiffrin. More interesting, Shiffrin has been struggling in the early races. I’ll speculate later on why I think Shiffrin is struggling.
In terms of the current trend in ski technique, it is not so much a case of Ligety and Shiffrin defining a new technique but more a case of them getting it right. By getting it right, I mean that they are skiing a technique that uses the innate, hard-wired processes of the human body, in particular, the basic movement pattern of alternating single-limb support made possible by the ability to develop a tensioned forefoot on the outside ski (DOT 4).
One aspect of this technique is the transfer of the load W to the proximate centre of the head of the first metatarsal where it acts in opposition to the point centre of Ground Reaction Force (COP) at the inside edge of the portion of the outside ski underfoot. The vector of the opposing force is perpendicular to the transverse aspect of the ski (DOT 7). This alignment of opposing forces is only possible when the proximate centre of the head of the first metatarsal is substantially aligned over the inside edge of the outside ski. The only way the centre of W can be aligned with the proximate centre of the head of the first metatarsal is through load transfer induced pronation at ski flat between edge change.
Due to the influence of Ligety and Shiffrin, World Cup ski technique is trending in a positive direction, as are skis. But the design of ski boots and modifications made to them continue to gather momentum in a direction that is antagonistic to load transfer-induced pronation.
“When the foot attempts to pronate inside the ski boot, it is often the case that the ankle bone will come to bear against the inner surface of the boot shell. When contact of this nature occurs, pain and other related complications usually result. Since the consensus of those skilled in the art of ski boot design and modification is that pronation or the rolling inward of the foot is detrimental, and, thus, undesirable, provision is not made to allow for such movement. Rather, the structure of the footwear is intended to resist or even prevent it.
“Thus, the problem with existing footwear arises due to the dynamic nature of the architecture of the foot. When the wearer is standing with the weight equally distributed between left and right feet so that the centre of mass of the wearer is manifesting itself in the centre between the feet, the architecture of the wearer’s foot assumes a specific configuration. As the wearer begins to shift his weight towards one foot so that the other foot bears proportionately less weight, the wearer’s centre of mass moves over the medial aspect of the weighted foot so as to assume a position of balance. In order for this movement of the wearer’s centre of mass to occur, the architecture of the weighted foot must undergo a progressive re-alignment. Existing footwear does not adequately anticipate this re-alignment of the architecture of the foot and thus such footwear inhibits the wearer’s ability to assume a balanced position.” – BACKGROUND OF THE INVENTION – US Patent No. 5,265.350 – MacPhail, November 30, 1993
A large camp in the ski industry appears to be of the position that the leg should ideally function as a lever with which to place and hold a ski on edge and apply forces to it. In this paradigm, the foot is viewed as a useless appendage, one that serves no purpose and only complicates the process of achieving a firm connection of the leg with the ski.
The relationship between equipment and technique is fragile at best. In the chicken and egg scenario, equipment enables sound technique. At the same time, equipment can disable sound technique once it has been established. The effect of equipment tends to become exacerbated in competition where races are won or lost by hundredths of a second. Here, seemingly minor changes can have major impacts on racer performance as reflected in results, which brings me to speculate on why Shiffrin is struggling.
It seems inconceivable that Shiffrin has lost her edge in competition. A more likely explanation is that she is literally not able to find her edge due to a change in some aspect of her equipment. Shiffrin comes across as intelligent, focused and disciplined. But like most racers today, she probably has minimal influence or control over her equipment, which is increasingly left to the experts. Indeed, the F.I.S. advises in their 2014-2015 rules document (http://www.artech-ski.com/fis/FIS-Alpine-Ski-Equipment-Rules-2014-2015.pdf), that, “Boot fitting for racers should be done by professionals, as there are many factors that play in to deciding on the correct fit.” I concur with the position of the F.I.S. that here are many factors at play in a ski boot. But the central issue is the affect of these factors on the physiologic function of the user. But this is an issue that does not seem to be appreciated within the ski industry in general, let alone by the F.I.S..
Instead, the prevailing mentality appears to be that solid technique can overcome equipment issues. This being the case, it is probable that her coaches, and even Shiffrin herself, may believe that correcting her current issues is a matter of making adjustments to her technique. But this is like saying that a skilled Formula One driver can win with an improperly tuned racecar. In order to maximize skier potential, the skier/ski equipment components need to be optimized as a system. They are not mutually exclusive. Yet, I have seen no evidence to date that this critical issue is even recognized. In ski racing, relative skier performance, not optimal skier performance, prevails. Here, luck appears to be the main factor in terms of skier/equipment synergy.
The following elements, which will be the subject of future posts, are characteristic of a sound ski technique.
- A transition phase between at the end of a turn to initiate load transfer to the inside (new) ski.
- Rotation of ski into the new turn initiated by load transfer to the inside leg while the ski is still on its inside edge.
- Extension to create load transfer and move COM forward so as to align Resultant, Centre of Load W and Ground Reaction Forces.
- One hundred percent of the load expressed on the new outside foot and ski at ski flat between edge-change.
- Coordinated ankle, knee, hip flexion at ski flat to initiate load transfer induced pronation
- External forces engaged at edge change to drive the torques into the turn and set up a cantilevered platform (DOT 4) of contiguous GRF to support the superincumbent body of the skier and provide reaction force for postural responses.
- The use of the inside leg as a strut with which to brace the pelvis so it can be oriented to assist in the alignment of R emanating from COM through the proximate centre of the head of the first metatarsal.
- Phased, multi-plane torques into the turn.
- Whole leg internal rotation from the pelvis coordinated with edge change.
- Achilles induced plantar aponeurosis tensioning (tension in the sole of the outside foot).
It is the synergy of these things that allows a skier to engage the process of innate flow balance (DOT 13) with its hyper-speed subconscious information bit processing rate.
“When I ski, it’s like a song. I can hear the rhythm in my head, and when I start to ski that rhythm and I start to really link my turns together, all of a sudden there’s so much flow and power that I just can’t help but feel amazing.”
I believe that some factor in Shiffrin’s equipment is causing her to make conscious corrections on course. Unless this issue is accurately identified and corrected and soon, she will find it increasingly difficult to ski with innate flow balance.