MIKAELA SHIFFRIN: THE POWER OF SHEAR FORCE


I am a huge fan of Mikaela Shiffrin, not because I view her as a goddess with mystical powers but because I admire her intelligence.

At the beginning of the 2014-2015 World Cup season, Shiffrin was in serious trouble. It was obvious to me that she had made some significant changes to her equipment prior to the start of competition.  Although it may sound harsh, I believe this is the best thing that could happened. The problems caused by these changes forced her to think about her equipment and especially her technique and how equipment affects it. The speed with which she turned around a bad situation is remarkable. Her winning margin of 1.68 seconds in the Snow Queen Slalom in Croatia, the biggest winning margin in the 10-year history of the event and an eternity for any World Cup race, should silence critics who claimed that she had lost her edge (she had lost the feel for her edge) or was suffering from a mental block.

Shiffrin’s comments  in a Team USA.org story, Shiffrin Dominates Field To Win Snow Queen Trophy ( http://www.teamusa.org/News/2015/January/05/Shiffrin-Dominates-Field-To-Win-Snow-Queen-Trophy) provide valuable clues as to her sudden quantum leap in performance. After changing  her boots and skis during a 10 day training camp in Italy Shiffrin commented, ”

I feel really comfortable on my feet right now after a lot of testing in Santa Caterina but also really great training.

With every single run that I take I get more confident…… My skiing is good right now, it’s kind of back on track and my equipment feels really good.

For the first time in my career, I just feel like I am in complete control of myself……… I feel like I am in a really great place right now.

Shiffrin’s accentuation of feel is significant as is the fact that she did, a lot of testing in Santa Catarina. These comments  indicate to me that she has connected the feel in her feet with the alignment of  W at ski flat with the proximate centre of the head of the first metatarsal of the new outside foot of a turn and and maintaining the alignment R and W with the proximate centre of the head of the metatarsal through the turn phase. If this is true, then she has a huge advantage over her competition because it is unlikely that they are able to feel what she feels.

So, why is Shiffrin suddenly not just skiing better than ever but far better than her competition? I believe an important factor is shear force. Seriously? Yes, seriously. While Shiffrin is clearly demonstrating sheer force in terms of the winning power of her skiing, I am actually referring to shear force in the context of a force acting in a direction parallel to a surface. Shear forces typically arise in the load points at the base of a truss under compression. The resulting tension in the unrestrained bearing points of the heel of the bottom chord (sole) of the truss cause the bearing points to spread away from the centre of the compression load. There is an important truss structure in the skier/ski equipment system. But I will save this for a future post.

The importance of shear forces in ski technique is that they creates fascial tension in the forefoot that potentiates small nerve proprioception, muscle power and, most important, act to stiffen the forefoot in a manner that enables rotation of the outside ski of a turn about a centre between the inner (medial) aspect of the head of the first metatarsal and the outer (lateral) aspect of the heel using whole leg, top-down, pelvis-driven, internal rotation. As I intend to demonstrate in future posts, this mechanism acts to extend the GRF acting along the inside edge out under the body of the ski thereby creating a source of GFR under the foot that the skier can use to balance on. This is the signature of the world’s best skiers. I will expand on this mechanism in a future post.

Other factors contributing to Shiffrin’s superior performance include:

Her boots

Given the importance of her ski boots, it was appropriate that a cameras zeroed in on a close shot of her boots at the start of the second run. They appear to be an older Atomic model, most likely her old boots. Given the fact that Shiffrin did testing at Santa Catarina, I think it probable that she did some experiments with changes in her boots because she is skiing far better now than she did last year and will probably continue to improve.

Shiffrins Boot

The set up of her boots is a huge factor. The screen shot below is of Shiffrin skiing straight down the fall line out of the start. The configuration of the elements of her body in terms of creating tension in the arches of her feet is nearly perfect. The reason stance in the fall line is significant is that the pressure exerted by the shins on the front cuff of the boot is minimal. The COM of the racer has to be over the feet and supported by the muscles responsible for maintaining an erect stance.

Shiffrin in fall line

This becomes obvious when her orientation is referenced to a level surface as shown in the graphic below. The red ball is my estimated location of her Centre of Mass. The force vector passes through the upper or proximal aspect of her tibia and continues through the proximate centre of the head of her first metatarsal. The key is the angle of the shank of her leg which must be achieved without applying significant force to the front of the cuff. This ensure that the triceps surae is in isometric contraction so that foot to core sequencing can occur. This issue will be the subject of a future post.

Screen Shot 2015-01-05 at 11.45.30 AM

In watching the video of Shiffrin on course moving from turn to turn, her fluid pendulum action and rhythm resembles the action of a metronome.

18 comments

  1. Dear skinetics, I have been following this blog with intense interest. As a junior racer back East, who competed in the old leather Hierling’s and now still compete 60 years later (Masters racing) in the modern Head Raptor B2/B3, I did find the transition (leather to plastic) fyi, my first plastic boots were the extremely uncomfortable and very difficult to fit Lange World Cup (circa 1966), very unrewarding. Technique and adaptive change was a long process. I do agree that boots are a personal issue, much more than the remaining and ever changing equipment (skis shape and sidecut being the primary factors). But as to the changes Miss Shiffren made, with obvious dramatic improvement in results, is, in my opinion, not just a change in boots but, also in the coaching staff and, thus, training patterns and procedures. But I wanted to ask how you determined that she changed boots, because the close-up shown of her boots is of that of this years model (the previous year’s model had a white star and the Atomic spelled out, not split like this years)?

    1. In the scheme of things, the ski boot comes first because it literally defines the operational parameters of the human lower limbs. Using the research vehicle we called The Birdcage, it was possible to instantly reduce a World Cup or Olympic champion to a struggling beginner or enable a beginner to use the same gross processes as a World Cup or Olympic Champion. Some may say that this would not be fair. I agree. But other intention or not, it happens even at a World Cup level as it did with Shiffrin. She said that she had a 10 day camp in Italy over Christmas where she made changes to her boots and skis, did tests and had excellent training. Exactly. In working with racers I found that subtle changes in boots could have dramatic results (good or bad) in competition that didn’t emerge in pre-season training. So I was paranoid about changing something that was working. If I wanted to try something new, I built a new pair of boots and had the racer take their old boots to training and races in the next season. That gave them a fall back if there were any signs something was amiss.

      When Shiffrin struggled at the beginning of the season, I speculated that she had made changes made to her equipment, boots and possibly skis. She later confirmed this. The question is did she make changes to her current boots as in pre-season changes then later reversing the changes? Or did she change to a new boot in the pre-season and then change back to her previous boot? I have no way of knowing. The fact that her boots have a certain appearance means nothing. When I worked with Langes, the race model was the XL-R. When Lange came out with a new model called the ZX-R I did some tests with some of the racers who were on the XL-R. While I expected there would be no difference there was. The racers didn’t like them. So I just put ZX-R badges on XL-Rs and no one knew the difference. What was inside the boots was nothing like the out of the box stock model. But race cars are like that. Lange has a stock of the old race models. Maize skis on them as do other World Cup racers. I would have loved to have seen what was in Giardelli’s Salomons.

      1. It was not my intention to question the veracity of your statements, just to ask if you had a more inciteful position or insider information. Yes, I agree that you can’t tell the quality of a book by just its cover and the shell of a boot, like the the topsheet of of a ski doesn’t tell the story of its components. In fact, using a great deal of your very informative blog (specificaly the discussion on the work you did with Pod) I recently modified my race boots to allow more forward (dorsiflexion) for my ankles and my balance over the skis (my coach emphatically confirmed this) has improved and my turn shape is much more tuned to what I have been trying to develop. True balance and control at all speeds. So thanks for your informational blog. Keep it coming.

      2. I am glad that you are finding information that is helping you. I get private communications from skiers in other parts of the world telling me the same thing. There is what amounts to a formula for arriving at the correct forward lean for a ski boot that I will describe in a future. For now, there is what I call the ‘reference forward lean’ position where the centre of the tibia in the knee joint (not the front of the knee cap) is over the center of the head of the first metatarsal (ball of the foot). The flexion space is behind the calf and should allow about 12 degrees of plantarflexion (rearwards flexion). Many racers have too straight a cuff that is made worse by cinching up the cuff buckles and power strap. The power strap should be used like the sling that arrests airplanes landing on a carrier. When your shin blows past the front reference from a sudden shock the power strap helps arrest shank movement. When everything is working right, you should not be aware of the cuff in any direction while skiing.

  2. Since I don’t even have the ‘peanuts’ that the big companies have for the $25,000 I have to do the measuring in my own way. If others look at the ‘birdcage’ and think it looks crude they should see some of the things I’ve skied on. I mean what’s the worst thing that can happen, I sue myself for crying out loud? Your method is better in the sense that it is a ‘third party’ gathering data without a prejudice (one hopes) and once you have the machine it saves time. Today in analyzing my efforts over the last few days I realize the truth in David’s boot work concepts. Never having met or formally trained with him, I can take the information I’ve read and it works, not incrementally, but phenomenally. Yes, I do write at times for some clarification which I receive, generously. And I’ll be the first to admit that having the pro do the work the results would be infinitely better but who is to say I could even get my boot in the door? I’d imagine there has to be a long line!! Now contrast this with when I worked in ski shops with formal, in person training and my efforts were so poor I was essentially asked to not make any more impressions of skiers feet for the foot beds. That worked well because the process was so primitive that it made no sense to me and I couldn’t see any scientific basis behind it for the $150 a pair that skiers were spending. I do have to admit I exaggerated in my last comment, there was a minority of techs that did very good work(in spite of the bad science behind the methods) and were actually willing to modify the final product if it appeared to need improvement. What got me thinking was when I followed the company line and sent a skier in to get footbeds to improve their skiing and it made it worse.

    The ‘science’ and legality connected with bindings is a joke too. Went to the training course and test for binding co. A and the test was open book. I could live with that because if sober and you have all night you can take the time to read the book if you have to. Binding co. B went through each question, in this fashion, the answer to #1 is B, the answer to # 2 is…. Thankfully I passed both tests and was ‘qualified’ to do the work. I bought a pair of used skis from friend without bindings, a former speed ski racer who tunes his skis pretty much daily. When I went to mount my own bindings and was plugging the holes, both hole patterns looked off. Getting out my squares and measuring devices it turned out both toe bindings were mounted ‘perfectly’ crooked by about an eighth of an inch, meaning the mounting jig was off. Would never have picked that up in his skiing but the point is that A) I can mount bindings crooked without a jig and B) as instructor it was illegal for me to touch a binding to release it if the skier was tangled up in a heap like a pretzel!! It’s a weird mentality when we keep doing things over and over because they are sacred cows to society but in reality aren’t even cows!

    1. As I said in one of my posts, when the data started to stream live from the Birdcage to the prototype laptop Toshiba had generously provided (remember, this was 1991), it was both satisfying and concerning to see the data on screen exactly as I had predicted before the tests had begun. Satisfying, because the data justified my considerable efforts to acquire an understanding of how we should ideally ski. Concerning, because I immediately realized that an independent, unbiased third party could use such a device to assess and analyze how ski specific equipment affects a specific user even to the point of isolating the effect of individual components of ski equipment. When someone puts a ski boot on their foot, it is next to impossible to determine how the boot affects them because of the amount of ‘noise’ created by structures that indiscriminately envelope the foot. The data from the Birdcage experiments from conventional boots fit with the Birdcage instrumentation package showed this. It was all but indiscernible garbage. But what was really happening came into sharp focus with the discrete contact, open architecture format of the Birdcage. The rapid evolution of CAD modelling and 3 D printing has made it possible to not only fabricate instrumented simulators that can capture data in real time during real life performances (See HOCKEY SKATE SMACKDOWN), the captured data can be used to model the effects of equipment on the user in a computer with software just as is done in forensic investigations of automobile crashes and the failure of structures.

  3. Hey Dave…read your response to Tyler. Would like to comment on ” at some point ‘fixed in neutral’ became part of the storyline”. Casting the TNJ in ‘neutral’ was the AMA (American Medical Association) response to footbeds. It was decided thiS was the best position for the foot too resist the forces in skiing. what really was going on was the foot was being manipulated +posted by people not formally trained. This is the province of podiatry! liability reared its head which led to podorthic licensing in the US in all nut 2states..Me.+Nh.

    1. I had never heard that before. Was it a mandate as in a best practices protocol or a recommendation? Do you have a reference to a document by the AMA on this or a link to one? Was there any rational behind this that you are aware of any especially studies in support of it?

      1. Latest update: David MacPhail wins again!!! Over the last couple days I operated on my left boot and did some more work on my right one, also replaced the rubber gasket I had installed at the tip of the overlap by the toes that was fried out during the boot stretch. Because of the difficulty of moving the shell far enough by the big toe area with my stretching equipment (and lack of knowhow!) I decided to remove the liner to the outside of my big toes which leaves only the shell between them and snow. Was supposed to ski with a friend today at a bit bigger area but we decided not to drive the extra miles because of the cold. I said I had to go regardless because the weather was perfect for freezing my toes if that was what would happen because scientifically one would think removing insulation makes things colder, not warmer. Friend decided to join me at the closer area so away we went. Temp was single digits, wind was gusty to at least 30mph (could always check the national weather if someone really cares), the lift was slow and the terrain is flat so that it doesn’t create much added body heat in the 30 seconds to the bottom. Results; I loved the improved skiing dynamics, the added ability to move because my feet were even more free mainly in the toe and metatarsal area from these adjustments. Strangely enough, my body with 5 layers of Underarmor and wool sweaters got chilly by the end BUT MY TOES DID NOT!!!!! Actually my previous comment didn’t mean to imply that I don’t understand the COMs etc, I’m just saying go try this stuff because most boot fitting I have found defies logic (what is said to be logic mostly is just those things that aren’t understood and/or don’t make somebody lots of money) because the results are all that counts in the end. And all these boot fitting items recommended by David in this blog I’ve never heard elsewhere and they all are integral parts of the equation to being able to ski the cement blocks marketed today. Last March, about 2-3 months before I learned about this blog, I made some changes in my boot board and then loosened the cuff by removing the power strap (turns out they are only good for carrying the boots) and undid the buckles to the point that I hit the cuff just before my ankles reach maximum flex. I’ve never had more fun skiing, until today! The beauty of this blog for me is that it’s saving me years of experimentation and quite frankly, things like making real space for the fore foot that I may never have figured out on my own. I thought my toes were free…NOT.

        As far as certified vs. not, you could take ten podiatrists, have them set the taler joint neutral and end up with twelve different positions. What I have found is that being off by a bit becomes a large problem when the finished orthotic is so rigid that there is no range of motion at all. This a theme which I repeatedly read in this blog; current accepted ski industry standards are, lock the feet with no movement at all. And guess who makes the orthotic after the doctor gets the correct impression, somebody in some lab who never has even seen the person. Also I have never once had the maker test me too see if they actually help or not because obviously they are 100% perfect 100% of the time as made. When I go back because they don’t or hurt; how dare I question the expert when all I do is ski on the stupid things. Pre-blog I started my recovery from a hip injury by removing my self-made orthotic. That helped and then loosening the boot cuff cured it. I reintroduced my orthotic which has no posting other than at the heel, once my hip was OK, which I liked better than no orthotic but if I didn’t make my own, I probably would not ski with one because all the ones I’ve had made and paid for were too rigid which wasn’t an issue until I figured out I could ski better if my feet could move as designed. That’s why I started making them myself after having worked in a ski shop and deciding I couldn’t make an prthotic that worked.

        Do I have a problem with any one questioning the content written in this blog or that I write? Not in the least, wouldn’t be the first time for me and maybe not for David. My opinion is go try it first, then try to figure out which of the opposing arguments is correct or is there some validity in all the different opinions. Also go back to the races Shiffrin wasn’t doing so well in and see if the commentators critiqued her equipment or her technique/training.

      2. You have neatly explained why I decided to invent a research vehicle that allowed the effects of the structures of a ski boot and interventions such as custom footbeds and orthotics to be tested under real life conditions against what I call the individual Performance DNA of a skier. This is the same approach that I used in the design process of the new cycling shoe just launched called Kinex. The first step in the Kinex process is to fit the client to a device called The Simulator then make adjustments that optimize muscle output and the transfer of force to the crank as confirmed by a real time data stream. Once the Performance DNA has been captured, it is used to create a formula with which to build the shoe. If someone were to suggest that a custom footbed or other intervention will improve performance it is a simple matter of mounting it on The Simulator then running it against the performance DNA metrics. If the intervention reduces the performance then it clearly does not perform as advertised.

        It has taken 2 decades to catch on but simulators are now being used in research to study human performance. The technology that existed in 1991, when we did the Birdcage studies, was crude compared to what exists today. And a sophisticated simulator with data collection can probably be made for less than $25,000. Peanuts. Those who make claims need to start making sure they can defend them. It is never good when someone else catches someone fibbing.

  4. Update: Last night I took out the scalpel and went to work on my spare liners. The spares are from a race boot, same brand as the original boot, so thus are even narrower and pointier than the original liners. I detested them from the minute I put my foot into them, even though I’d skied in that model a number of years ago on a daily basis!! A little bit of slicing made the toes much better and admit I’m a bit reluctant to cut the whole front off the liner due to having had a severely frost bitten toe a couple of years ago from a simple opening the seam by my big toe. (just to get the doctors and doubters going, God saved my big toe because it was so bad that I knew the only chance I had was prayer!!) Next I went to work on trying to get enough room in the shell to allow my big toe to be in its’ natural position. I was able to get it better but not perfect after 2-3 hours of work. Since that took me so long I decided the best action would be to leave my newly activated left foot alone and compare them on snow (ice or something like that!) Today was the ideal day, bit of fresh snow but more important the temp was in single digits F. I really liked the ability to actually use my big toe as it’s designed, then added the instep fill pad to the right boot also, and definitely liked the right foot better than the left. Could really feel the improvement even though I can tell that there is much room for improvement even after all that time spent. I was impressed by the fact that while my hands got uncomfortable from the cold, my right toes felt a bit chillier than the left foot with the untouched liner, but definitely warmer than my hands!! These are my conclusions: ski boots are a pain in the ___ because the guys making them are clueless. All foot wear doesn’t give enough space in the right place for the toes unless one goes up several sizes. I’ll go get the next size boot most likely. My left boot isn’t anywhere close to perfect, still I can see how beneficial it will be when my forefoot is properly freed up and have the tongue work done appropriately. Even though my mother always advocated roomy toe space in foot wear, I got lulled into accepting constriction in that area in all my footwear, I guess because the status quo is the feet can’t do anything right unless you have the ideal mega $$$ foot wear. As this whole saga with Mikaela Shiffrin’s slalom racing proves, the outfits manufacturing the ski boots don’t even have a clue what they are doing and why. The best racers for the most part are the ones that accidently end up in the equipment that actually works for them…. sort of! And when a racer is successful, switches gear and falls apart, the techs can’t even pinpoint where the problem lies to fix it!! Last item; anyone reading these blogs that can’t grasp the COM, W, etc. (that would be me!), just try some of David’s boot stuff and it’ll be hard to doubt anything he writes!! Thanks for all David, I’ll keep ya all posted on future developments!! P.S. There are some pretty smooth slalom runs on you-tube of Bode Miller in the early years of this century by the way.

    1. Thanks for the feedback Michael. Here is a metaphor that explains the current situation with Shiffrin. Let’s suppose that manufacturers of weight vests convinced the competitive swimming associations that their products would make their swimmers faster. This is not really any different than the story that immobilizing the joints of the foot makes it function best for skiing (Making the foot dysfunctional makes it function better? Seriously?). If all the competitive swimmers in the circuit started wearing weight vests that are close to the same weight then the best swimmers would still win because it is relative. But if one racer stopped wearing a weight vest…… well, that would be a whole different matter wouldn’t it? Mikaela Shiffrin just figured out she was wearing the equivalent of a swimmer’s weight vest. Maybe the one she was wearing was lighter than the vests of her competitors. But she was still wearing a weight vest. Now she isn’t.

      1. Ok, so the metaphor …. We know she fixed something and it may have improved her stance etc, but did she do so much to have remove a weighted vest? I have no idea but the suggestion is intriguing.

        I am new to your blog over the last few wks and like Michael try to hang on with the descriptions. I’ve been working on actionable items like extension off inside ski and hips forward at time of flat ski. Also tried looser top buckles … This is novel!

        Been pondering the extent of extension possible in quicker slalom turns ….

        Anyhow, thanks!

      2. Tyler, welcome to The Skier’s Manifesto. Since you are new to the blog, you probable haven’t found the posts on the Birdcage experiments. Here’s a link to one – http://wp.me/p3vZhu-kD

        Two things influenced my perspective on ski technique and ski equipment. First, I was a runner before I skied. Like everyone else, I ran in flats. These were like low cut basketball shoes. The soles were flat and thin (no arch supports) with no heel drop (elevated heel). I never had knee pain or running injuries and I can’t recall my running mates having any until they started running in the new flared, raised heel jogging shoes that were marketed as designed for running and jogging. All of a sudden, running magazines were running feature articles on running injuries and overpronation is bad which eventually morphed into ‘any and all pronation is bad’. I didn’t even know what pronation was back then. I had never heard of the term.

        The next thing that influenced me was easily becoming an elegant, expert skier using low-cut leather boots only to be reduced to a struggling beginner in the new high cuff rigid boots that were supposed to make skiing easier. Others suffered a similar fate. About the same time, I began to see the skier paradox. Out of shape friends skied well and easily while fit athletic friends struggled. The storyline that eventually became the standard industry line is that the foot functions best in skiing when its joints are immobilized in the ski boot which was supposed to equate with an orthopedic splint. At some point, ‘fixed in a neutral’ became part of the story line. It sounded good to me. If everyone says the earth is flat, then it must be flat……. right? But when I did what was supposed to be the optimal (and I did it exceptionally well) it mostly didn’t work especially for me. When I looked for evidence in the form of studies that showed that attempting to immobilize the joints of the foot provide benefits for skiing I couldn’t find any. In fact, I couldn’t really find much of anything in support of the objectives of ski boots and boot fitting which I later started to equate with weight vests on swimmers. So I started going in the opposite direction.

        The lack of evidence provided the impetus for me to formulate a hypothetical model of how the mechanics, biomechanics should work in the dynamic physical environment of skiing. As part of a project to try and design a ski boot based on sound principles, a biomedical engineer and I designed an instrumented research vehicle we called The Birdcage. The Birdcage allowed us to study how the human balance system responded to challenges caused by impeding joint actions during actual ski maneuvers. The Birdcage replaced the ski boot. When the weight vests were removed the improvement in the efficiency and ease of skiing was astounding. The problem was and still is that weight vests have become an integral and accepted part of skiing.

      3. waht was Shiffrin wearing wrong? I just arrived in this blog and besides my english comprehension I’m feeling lucky to find it!

      4. Welcome to The Skier’s Manifesto Joan. Shiffrin made changes in her boots and skis before the start of the 2014-15 World Cup season. She struggled terribly in the first races. Then she made changes over Christmas at a 10 day camp in Italy. I think it probable that she returned to her old boots and made changes to her skis. Like many who found my blog, you were probably expecting the ski industry equivalent story of The Earth is Flat because everyone says it is. I was the impetus behind pioneering research done in 1991 that used an instrumented research device that replaced the ski boot to study the mechanisms of balance in World Cup racers and Olympic Champions. The findings of these studies challenged the design and modification of ski boots and the principles on which ski technique is based. You can read about this under Appendix and About Me under the left side of the blog title bar.

  5. I’ll be interested in your thoughts and observations about minimal shin pressure on the boots.

    Thanks.

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