NEW INSIGHTS INTO THE BIOMECHANICS OF WALKING AND STEPS IN THE SKI TURN

Comments made by S.S. Komissarov in his paper, Dynamics of carving runs in alpine skiing. The centrifugal pendulum in conjunction with a critical examination of the biomechanics of the walking cycle and subjective on-snow experiments I did last ski seaon has given me insights into the mechanism that enables fluid dynamic skiing with directional control.

A telling statement by Komissarov is that in the fast skiing typical of FIS WC racers’ rhythmic carving turns are still possible but balanced carving turns are no longer possible. Komissarov further states that during rhythmic carving turns a skier is never in balance. I would modify this statement to posit that during rhythmic carving turns a skier is only in what can be described as a state of dynamic balance wherein neurobiomechanical processes effect tight control over variances in the orientation of the transverse plane of the base of the edged outside ski as it pertains to the alignment of the vector of opposing applied and reaction forces for a few milliseconds.

These insights explain why static balance exercises done on one foot, lateral side to side jumps where a subject lands and balances on one foot and even one ski turn exercises don’t equate with the dynamic mechanism responsible for the fluid movement of dynamic skiers.

A critical examination of the walking (aka gait) cycle raised issues that as far as I know may never have been explored. These issues have potential implications for the role of steering in the alignment of the pendulum vector of COM with the transverse aspect of the outside ski as it pertains to the edge angle in carving and the stiffening of the outside foot and leg that enables powerful carving forces to applied to the outside ski that when released act can act as catapult mechanism to propel the skier into the next turn.

Pelvic rotation appears to be a key component in the dynamic processes of both walking and skiing.

In my next post I will start to explain how I believe pelvic rotation in walking relates to pelvic rotation in a ski turn and what the differences are.

 

IS DYNAMIC SKIING A FORM OF WALKING?

The text below is from a sub page I put up on the home page in 2014 in which I posited that elite skiers use the same hard-wired processes as walking.

It was only recently after I connected pelvic alignment with the ball of the outside foot of a turn achieved by steering the foot into position with COM to create an alignment with the fall or gravity line did I finally put the last piece of the puzzle in place.

As bipeds, we propel our bodies forward by moving from one fascially tensioned base of support with foot to core sequencing on one foot to another fascially tensioned base of support with foot to core sequencing.

Dynamic skiing uses the same basic pattern. In skiing, we need to establish a fascially tensioned base of support with foot to core sequencing on one foot in order to be able to move with precision to another fascially tensioned base of support with foot to core sequencing on another foot. As far back as the 70’s, the famous French ski technician, Patrick Russell, said that the key to effective skiing is to ‘move from ski to ski’. What Russell was really alluding to is the process of alternating single limb support.

Ever since alpine skiing became formally established, it has been known that the best skiers move from the outside ski of one turn to the outside ski of the next turn. Although this may sound simple enough, the key to being able to effectively move from ski to ski (foot to foot) is the ability to establish a fascially tensioned base of support with foot to core sequencing one one foot and then use it to move the body or Centre of Mass to the new outside foot (current uphill ski) of the next turn. Good skiers do this so seamlessly that turns seem to have no beginning or end. The turns just flow together. When viewed in the context of stance and swing phases, the resemblance to walking becomes apparent

How to make skiing as intuitive as walking is what this blog is about. I devoted an entire series of patents to this subject commencing with US Patent No. 5,265,350 and associated international patents on the elements of a minimal ski boot necessary to accommodate the process of establishing a fascially tensioned base of support with foot to core sequencing on one foot and transitioning seamlessly back and forth between bipedal and monopedal stances.

The ability to balance multi-plane torques on the outside leg of a turn is, and continues to be, the secret of the worlds’ best skiers including Toni Sailor, Nancy Greene Raine, Pirmin Zubriggen and, today, Mikaela Shiffrin, Lindsey Vonn and Ted Ligety to name but a few.

A REVIEW OF GAIT CYCLE AND ITS PARAMETERS – Ashutosh Kharb1, Vipin Saini2 , Y.K Jain3, Surender Dhiman4 – https://ijcem.org/papers72011/72011_14.pdf

Dynamic loading of the plantar aponeurosis in walking – Erdemir A1, Hamel AJ, Fauth AR, Piazza SJ, Sharkey NA. – https://www.ncbi.nlm.nih.gov/pubmed/14996881

Active regulation of longitudinal arch compression and recoil during walking and running – Luke A. Kelly, Glen Lichtwark, and Andrew G. Cresswell – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4277100/

The Foot’s Arch and the Energetics of Human Locomotion – Sarah M. Stearne, Kirsty A. McDonald, Jacqueline A. Alderson, Ian North, Charles E. Oxnard & Jonas Rubenson – http://www.nature.com/articles/srep19403

Shoes alter the spring-like function of the human foot during running – Kelly LA1, Lichtwark GA2, Farris DJ2, Cresswell A2. – J R Soc Interface. 2016 Jun;13(119). pii: 20160174. doi: 10.1098/rsif.2016.0174. – https://www.ncbi.nlm.nih.gov/pubmed/27307512

The Science of the Human Lever: Internal Fascial Architecture of the Forefoot with Dr. Emily Splichal – https://www.youtube.com/watch?v=_35cQCoXp9U

 

 

 

 

FIT VS. FUNCTION

With rare exceptions, the consistently stated objective of boot-fitting systems and modification efforts is to create a perfect fit of the foot and leg of a skier with the rigid shell of a ski boot by applying uniform force to the entire surface of the foot and the portion of the leg in the boot in what pits Fit against Function. The end objective of the Perfect Fit is to achieve a secure connection of the leg of the skier with the ski. In the name of achieving a secure connection of the foot with the ski, the function of the skiers’ foot has become unitended collateral damage.

But boot design and boot fitting effors didn’t start off with the intent of compromising the physiologic function of the foot. It just sort of happened as a consequence of the limited ability to change the shape of the rigid plastic ski boots to address issues of user discomfort when plastic boots were first introduced. The new plastic boots worked well for some skiers. But for most, myself included, my foot moved around inside the shell when I tried to ski. The feeling of insecurity created by the looseness made skiing with any semblance of balance or control impossible. The fix seemed to be a simple matter of trying to figure out where to place a pad or pads between the foot and shell to stop the foot from moving.

In 1973 when I first started tinkering with my own ski boots the craft of boot fitting barely existed. Like myself, those who were trying to solve the problem of a loose fit were doing proceeding by trial mostly with alot of errors. After what seemed like unending frustration from many failed attempts at trying to find and then solve the source of my loose fit, a consensus began to emerge within the ranks of the ski industry that the easiest and quickest solution was a process that would create a tight fit of the foot everywhere with the boot instead of wasting time trying to find the elusive right place to add pads. The Perfect Fit was born.

Injected foam fit was first off the mark as a Perfect Fit solution. But injected foam fit wasn’t tight or precise enough for my standards. So I tried to take the Perfect Fit to the next level with Crazy Canuck, Dave Murray. I started the process by carefully trimming and laminating together pieces of sheet vinyl to form a matrix of solid material that I inserted into the liners of Mur’s boots. The process took about 2 weeks of painstaking effort. Finally, I satisfied that Mur’s feet were securely locked and loaded; ready for the best turns of his life. The result? One of the world’s best racers was instantly reduced to a struggling beginner, the exact opposite of what I had expected! This experience served as a wakeup call for me; one that caused me to rethink what I thought I knew and question whether the Perfect Fit was the best approach or even the right approach.

I started looking for alternate ways to restrain the foot so it was secure in the shell of a ski boot without compromising foot function. In 1980 when I was building a pair of race boots for Crazy Canuck, Steve Podborski I literally put my finger on the solution when I pressed firmly, but not forcefully, on the instep of his foot just in front of the ankle and asked if he thought we should try holding his foot like this in his new race boots. Without the slightest hesitation he said, “That feels amazing. Let’s do it!”

It took me more several few days to fabricate a system to secure Pod’s foot in his boots by loading the area of the instep that I had pressed my finger on. The problem we faced when the system was finished was that the liner made it impossible to use the system without modifying it. So a decision was made to eliminate the liner except for the cuff portion around the sides and back of his leg which I riveted to shell. At the time I wasn’t sure the system would even work. So I made a pair of boots with fined tuned conventional fit as backup. A boot with no liner seemed like an insane idea. But Podborski was not only able to immediately dominate his competition on the most difficult downhill courses on the World Cup circuit but go on to become the first non-European to win the World Cup Downhill title. Even more remarkable is that in his first season on the new system he was able to compete and win less than 4 months after reconstructive ACL surgery.

What I discovered set me off in a whole new direction. Pressing on the instep of Podborski’s foot activated what I later found out is called the Longitudinal Arch Auto-Stiffening Mechanism of the Foot. This system is normally activated as the mid stance (support) phase of walking approaches late mid stance where the foot is transformed into a rigid structure so it can apply the forces required for propulsion. As I learned about the processes that transform the foot into a rigid lever I began to understand how interfering with the function of the foot can compromise or even prevent the Longitudinal Arch Auto-Stiffening Mechanism from activating and, in doing so, cause the structures of the foot to remain ‘loose’ regardless of any efforts made to secure it.  A rigid foot is necessary to effectively apply force to a ski.

The graphic below shows a sketch on the left from Kevin Kirby, DPM’s 2017 paper, Longitudinal Arch Load-Sharing System of the Foot (1.) Figure 44 A on the right is from my 1993 US Patent 5,265,350.

The above graphics clarify the details of the arch loading system I first disclosed in my US Patent 4,534,122. This system challenges the current Perfect Fit paradigm in which the physiologic function of the foot is compromised in an effort to try and achieve a secure connection of a skier’s foot with the ski.

Figure 44A above shows the principle components of the arch loading system which is comprised of a number of complimentary elements. I will discuss these elements in my next post which will focus on solutions.

  1.  Kirby KA. Longitudinal arch load-sharing system of the foot. Rev Esp Podol. 2017 – http://dx.doi.org/10.1016/j.repod.2017.03.003

 

TRANSITIONING FROM FIT TO HIGH PERFORMANCE FUNCTION


That footwear can negatively impact the physiologic function of the user has been known for many decades. But the issue of the effect of footwear on athletic performance came into sharp focus in 1987 with the publication of the medical textbook, The Shoe in Sport (published German in 1987 as Der Schu im Sport). The Shoe in Sport brought together the collective expertise of 44 international authorities on orthopedics and biomechanics to focus their attention on the SHOE PROBLEM in the context of problems shoes can cause for athletes in terms of compromising performance and contributing to injury. The Shoe in Sport focusses on the medical orthopedic criteria in offering guidelines for the design of shoes for specific athletic activities including skiing and ice skating.

In the Introduction to the Shoe in Sport, Dr. med. B. Segesser and Prof. Dr. med. W, Pforringer state that the findings in the textbook should enable the interested reader to distinguish between hucksterism and humbug on the one side and the scientifically sound improvements in the athletic shoe on the other. The Shoe in Sport made it abundantly clear that it is not a question of if structures of footwear will affect the physiologic function of the user, it is a question of how structures of footwear will affect the physiologic function of the user and especially whether they will compromise athletic performance and/or contribute to injury.

With regard to guidelines for ski boots, the international authorities on orthopedics and biomechanics who contributed their expertise and knowledge to Part IV The Ski Boot took the position that, among a number of other things:

  • ………. the total immobilization by foam injection or compression by tight buckles are unphysiologic.
  • The ski boot and it’s shaft must be adapted to the technical skill of the skier, and the technical skills of the skier must be adapted to the preexisting biomechanical functions of the leg and the foot.
  • It (the design) should not make compromises at the expense of other joints ………
  • It (the ski boot) must represent the ideal connecting link between man and ski (steering and feedback).

The position of international authorities on orthopedics and biomechanics on the medical and biomechanical criteria for ski boots was succinct, concise and unequivocal:

…….total immobilization by foam injection (implying by any means) or compression (of the foot) by tight buckles are (both) unphysiologic.

Dr. E. Stussi,  Member of GOTS and Chief of the Biomechanical Laboratory ETH, Zurich, Switzerland made a prescient statement with implications for the future of knee injuries in skiing:

Improvements in the load acting on the ankle (implying load from improved fit) make it biomechanically very likely that the problems arising in the rather delicate knee joint will increase.

While the international authorities on orthopedics and biomechanics who contributed to The Shoe in Sport provided valuable guidelines for the design of the ski boot they did not offer a specification that would assist designers and those who work with ski boots in meeting the medical and biomechanical criteria in the guidelines. My hope and intent was that the Birdcage studies and the content of my US Patent 5,365,350 (issued on 11-30-1993, expired on 12-28-2005) would serve as a foundation on which to build a specification that would enable the structures of ski boots to be adjusted to accommodate the personal functional requirements of the skier.

The steps in my transition from Fit to High Performance Function

After the unprecedented success of my dorsal loading invention with Crazy Canuck, Steve Podborski, I used the same system with similar success in the boots of a small number of other racers. I also incorporated this system into my own and my spouses’ ski boots in conjunction with suitable liner modifications and a reduction of the ramp angle of the boot boards to just under 3 degrees which I had identified in about 1978 as the maximum angle for skier performance. (NOTE: Since I wrote this post I have reduced the delta angle of my Head boots in stages with improvements in performance. It is currently close to zero.)

I can’t recall exactly when, but about 20 years ago I decided to move away from Lange ski boots. I purchased a pair Head World Cup 335 mm ski boots for myself and a pair of Head X-80 295 mm ski boots for my spouse. I say built because to me ski boots are raw material.

I had to completely disassemble the Head X-80s and drastically modify and reconfigure the components to adapt them to the morphology of my spouses’ feet and legs. The process took me about 35 hours. I was able to modify my Head World Cup liners to make them work without the same degree of modification. I made a dorsal loading system for my spouse similar to the one I made for Steve Podborski’s Lange ski boots.  But I was able to modify the existing Head tongue so it would adequately load the dorsum of my foot. The reason I went this route is that the shell of my Head World Cup boot is very stiff. This makes inserting my size 12 US men’s foot and a dorsal system, like I fabricated for my spouse, challenging. In the order of things the dorsal system is inserted after inserting the foot in the shell.

The photo below shows my Head liner after initial modifications.

The photo below shows the Lange tricot liner I used in my spouses’ Head boots on the left with no modification other than removing the Lange flow fit pads in the side pockets. I was unable sufficiently modify the liner that came with her Head X-80 boot. The version on the right in the photo below is the same liner after modifications i made for it work with the dorsal system shown in the photo underneath. The dorsal system in itself took many hours of painstaking effort to fabricate and fine tune.

With our modified Head boots fit with my dorsal loading technology my spouse and I would easily be classified as expert skiers. As recreational skiers with skiing limited to 10-15 days a season, most skiers would have no incentive to question the adequacy of their boots or especially devote time and effort towards finding ways to reach a higher level of performance. To the contrary, I found it disturbing that the ability to ski better than the majority of skiers fostered an intoxicating sense of superiority. But I knew what I didn’t know and I knew that I still had a lot to learn. In my mind, the transition required to realise our full performance potential was not yet complete.  I knew that the potential for improvement has no boundaries.

The transition to High Performance Function continues In my next post……….

THE ELEMENTS OF FLUID SKIING

A recent paper, Dynamics of carving runs in alpine skiing. The centrifugal pendulum by S.S. Komissarov, provided me with insights as to the differences between elite and lesser skiers.

Komissarov clarifies that the context of proficient skiers being well-balanced simply describes the observation that the skiers do not appear to be in danger of falling. The signature of good skiers is that they move effortlessly from turn to turn in a smooth, continuous rhythmic manner much like a metronome or inverted pendulum.

A key point is Komissarov’s comment that elite skiers somehow manage to ski faster than the theory of ideal carving predicts. He also states that the fluidity of the pendulum action of the elite skier does not actually require a forceful participation from the skier and that the skier has to make sure that they do not inhibit this natural process but just “get on board and enjoy the ride!”.

The reference to fluid skiing being a natural process requiring no forceful (conscious) participation from the skier in terms of the associated neurobiomechanics responsible for the pendulum action is one reason why I am shifting the focus of my blog away from ski technique (which is consciously mediated process) to the elements of fluid skiing and especially factors that interfere with the natural processes that enable humans to ski as easily as they walk so that analyses can focus on the why not the what.

 

THE SKIER’S MANIFESTO: REBOOT OR DELETE?

Thank you for all who have commented. I listen and I hear you.

I started this blog as a manifesto for skiers to interact and contribute to the betterment of this great sport. I view knowledge as dynamic. Positions on issues should change in response to new and better information. Without this process learning cannot happen.

A significant challenge to making the Manifesto serve this purpose is that it has been difficult for me to know the nature of the information my readers are seeking and whether my posts are providing this information or even resonating with my readers. When put up a post I need to get feedback, suggestions and yes, criticism. If you don’t agree with my position on an issue please tell me. As a critical thinker (self-critical) I always entertain the posssibility that my position on issue is wrong. At the very least  my explanations may not be clear. If this is the case, I need to know.

If you want me to post on a certain subject, please let me know. Without this information I could be wasting my time.

The uncertainty as to the nature of the information my readers are seeking or subjects that will be found in search engines has resulted in post threads that are disjointed as expressed by the comment below from a follower:

While the blog might be improved by some minor rearranging of the sequence of blogs, the important thing is that the information is in there. You have, in fact, suggested sequences for the practical application of several principles, boot fitting for example.

An easy way for me to address this issue is to repost existing posts in a sequence that will group them together according to the subject. After I respost the older post I can edit it in response to comments. So instead of deleting the blog I am proposing culling some posts and reposting and collating existing posts. But I can’t do it without your input and especially your suggestions.

I believe a good starting point is a discussion of how our hard-wired mechanism for walking applies to skiing and especially what is called steering. Does everyone agree? If not please suggest a subject.

 

THE SKIER’S MANIFESTO COMES TO AN END

After a lot of reflection I have come to the difficult decision to permanently delete The Skier’s Manifesto.

I started The Skier’s Manifesto in May of 2013 with the fervent hope that it would connect with skiers and serve as a catalyst for a diverse, integrated, science-based approach to ski technique and the design of ski equipment. But after 7 years the number of followers of the Skier’s Manifesto is less than 900.

In 2013 I knew that equipment played a significant role in sker performance. But I had no idea of the number of factors that had to be optimized to enable an elite level of skier performance. Nor did I realize how seemingly subtle factors like one tenth of a degree changes in ramp angle (zeppa + delta) could have such a powerful effect on neuromuscular function.

But the most significant factor is that I have found it all but impossible to offer solutions to the myriad of issues that can and do affect skier performance. To do this would take the coordinated effort of a team of professionals.

Finally, the devastating impact on skiing and ski racing of the recent corona virus outbreak in combination with a declining skier market has made it highly unlikely that skiing will ever make significant changes. While there is a wealth of information on the Skier’s Manifesto I have concluded that it serves no worthwhile purpose because there is no practical way to apply it in a sequential, coordinated manner.

Thank you to those who have followed my blog. I tried my best to make a contribution to the knowledge base of skiing. But it is time to move on. I will be permanently deleting the Skier’s Manifesto in the next few days.