FREEMOTION FLEX CURVE OPTIONS – PART 2


In The Shoe in Sport, the detached, objective assessment of the conventional ski boot articulated in Part 6, The Ski Boot, by preeminent authorities on biomechanics and safety served to support my conclusions of the past 10 years that little of what forms the basis of knowledge in skiing can be defended. This made me acutely aware of the dangers of going forward with a concept for a new ski boot that could not defended with a validated hypothesis based on principles of applied science and especially data captured during actual ski maneuvers that could be readily and consistently reproduced by others.

Key critical comments made in Part 6 of The Shoe in Sport, (first published in 1987 in Germany as Der Schuh im Sport – ISNB 0-8151-7814-X ) follow below as a prelude to the discussion of the Birdcage format as a basis for flex options for the FreeMotion ski boot and ski boots in general.


Biomechanical Considerations of the Ski Boot (Alpine)

Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland

  • Correct flexibility (of the boot shaft) is not the whole answer. The functional anatomy of the ankle joint must also be an important consideration. If the axis of flexion of the ankle joint is not precisely in line with the axis of flexion of the shaft, an unfavorable lever ratio will ensue, and the advantages of flexibility will be lost.
  • If flexion resistance stays the same over the entire range of flexion of the ski boot, the resulting flexion on the tibia will be decreased. With respect to the safety of the knee, however, this is a very poor solution. The increasing stiffness of the flexion joint of the boot decreases the ability of the ankle to compensate for the load and places the entire load on the knee.
  • Improvements in the load acting on the ankle make it biomechanically very likely that the problems arising in the rather delicate knee joint will increase.
  • From a technical (skiing) point of view, the ski boot must represent an interface between the human body and the ski. This implies first of all an exchange of steering function, i.e., the skier must be able to steer as well as possible, but must also have a direct (neural) feedback from the ski and from the ground (snow). In this way, the skier can adapt to the requirements of the skiing surface and snow conditions. These conditions can be met if the height, stiffness, angle and functions (rotational axes, ankle joint (AJ)/shaft) of the shaft are adapted, as well as possible to the individual skier.
  • The modern ski boot must be designed from a functional point of view, i.e., the design must take into consideration the realities of functional anatomy (axes etc.).
  • It (the design) should not make compromises at the expense of other joints (length of shaft, flexibility and positioning).
  • It (the ski boot) must represent the ideal connecting link between man and ski (steering and feedback).

Kinematics of the Foot in the Ski Boot – Professor Dr. M. Pfeiffer – Institute for the Athletic Science, University of Salzburg, Salzburg, Austria

  • The shaft of the boot should provide the leg with good support, but not with great resistance for about two-thirds of the possible arc, i.e., (12 degrees) 20 to 22 degrees. Up to that point, the normal, physiologic function of the ankle should not be impeded.
  • Because of its effects on the foot, the arc described by the shaft is divided into a “lead segment” and into a later “lever segment”.
  • Forward sliding of the foot should not be possible. There should also be no loss of contact of the sole and no decrease in the “feel”.
  • Previous misconceptions concerning its (the boot shafts) role in absorbing energy must be replaced by the realization that shaft pressure generates impulses affecting the motion patterns of the upper body, which in turn profoundly affect acceleration and balance.
  • Correct positioning of the foot is more important than forced constraint and “squeezing” the foot. This will prevent the misuse of the ligaments and weakening, particularly of the fibular musculature and ligaments. (This will also explain why even competitive skiers can suffer ankle sprains while engaged in light athletics or even just in everyday activities.)
  • When the lateral stability of the shaft (the leg) is properly maintained, the forces acting in the sagittal direction should not be merely passive but should be the result of active muscle participation and tonic muscular tension. If muscular function is inhibited in the ankle area, greater loads will be placed on the knee.
  • 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.
  • The medical requirements with respect to sports should not be construed as criticism of the boot industry. It is hoped that they are contribution to the development of a ski boot designed along anatomical principles. This goal has not yet been achieved.

Ski-Specific Injuries and Overload Problems – Orthopedic Design of the Ski Boot –  Dr. med. H.W. Bar, Orthopedics-Sportsmedicine, member of GOTS, Murnau, West Germany

  • Few forms of athletics place as high demands on the footwear used in their performance as alpine skiing. It (the ski boot) functions as a connecting link between the binding and the body and performs a series of difficult complex tasks.
  • Investigations by Pfeiffer have shown that the foot maintains some spontaneous mobility in the ski boot. Thus the total immobilization by foam injection or compression by tight buckles are unphysiologic.
  • The boot must assure freedom of mobility to the toes. This is accomplished by having a large enough inner shoe. Only in the case of major congenital or post traumatic deformities should foam injection with elastic plastic materials be used to provide a satisfactory fixation of the foot in the boot.

Sports Medical Criteria of the Alpine Ski Boot – W Hauser, P. Schaff, Technical Surveillance Association, Munich, West Germany

  • Many alpine skiers have insufficient mobility in their knees and ankle. The range of motion, particularly in the ankles, is much too small. This results in a static, stiff run. It does not correspond at all to the ideal of a wide range of mobility in the area of the knee and ankle, which was proposed and taught during early alpine ski lessons. Even the best diadactic (patronizing) methodology is not always successful in imparting to the student the full range of motion. The lack of proper technique seem so often is not due to a lack of ability, but to an unsatisfactory functional configuration of the shaft in so many ski boots. This is particularly true in models designed for children, adolescent and women.
  • In the future, ski boots will be designed rationally and according to the increasing requirements of the ski performance target groups.

The comment Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland 30 years ago has turned out to be prescient:

  • Improvements in the load acting on the ankle make it biomechanically very likely that the problems arising in the rather delicate knee joint will increase.

Unfortunately, Stussi’s warning does not appear to have been heeded.

In an article called Getting Serious About Skier’s Knee (Ski Tech, October 1993), Andy Bigford states, “Horror stories about ACL injuries are a dime a dozen” and “Victims tell of the cost involved (the whole package can run to $50,00 per injury), the difficulties of rehab, the lost work time and the fear of never being able to ski again”. Bigford goes on to point out that not everyone is convinced that the stiff boot-aggressive ski combination is totally at fault; that ACL injuries in the late ’80s and early ’90s came when softer (flex) and ‘more forgiving’ rear entry boots were popular.

Bigford ends his article by stating that the (knee) problem needs to be solved without scarring away skiers, but “If something isn’t done, they (skiers) will have plenty of reason to be scared”.

More than 20 years later, the cover heading What’s New With Knees (December 2016 Ski Canada magazine) is the lead-in to a feature article called Tear and Repair. The article header  states, “With knee injuries so commonplace, especially among skiers, the medical world is constantly updating procedures and surgical techniques for the big fix. The take away message from Tear and Repair  appears to be that the solution to knee injuries is not addressing the cause, it is repairing the resulting damage.

In the same magazine, a comment under Short Turns (Save Your Knees) states: “If you haven’t had a serious knee injury, you likely know someone who has”.  The take away message appears to be that knee injuries are part of skiing. Get used to it!

If my next post, I will discuss how the knowledge gleaned from The Shoe In Sport influenced my thinking on the design criteria for a new ski boot, in particular, shaft configuration and resistance to the rotation while creating an awareness of the need to be able to defend my design criteria with principles of applied science data acquired during actual ski maneuvers.

 

One comment

  1. Dear Dave,

    Happy New Year and a belated hope you had nice Holiday.

    This quote from W Hauser, P. Schaff, caught my eye.

    “Many alpine skiers have insufficient mobility in their knees and ankle. The range of motion, particularly in the ankles, is much too small. This results in a static, stiff run. It does not correspond at all to the ideal of a wide range of mobility in the area of the knee and ankle, which was proposed and taught during early alpine ski lessons. Even the best diadactic (patronizing) methodology is not always successful in imparting to the student the full range of motion. The lack of proper technique seem so often is not due to a lack of ability, but to an unsatisfactory functional configuration of the shaft in so many ski boots. This is particularly true in models designed for children, adolescent and women.”

    I would take a rather contrary view here and say the problem comes not from the boot design but a lack of technique. That is not because I disagree with Herr. Schaff.
    The modern skiing didactic does not really teach the hard, strong, or tensioned arch which if I understand it correctly is only induced when a certain forward range of shank motion and COM is achieved. This in turn sets up a chain reaction through the legs into the torso. Without this the skier can not attempt optimal form(s) or balance.

    The arch concept is not widely taught or understood. Therefore there is not a demand for footwear that meets the basic requirements for optimal skiing. Without this basic understanding it will be a matter of chance whether ski enthusiasts purchase or even know to adjust boots for full range of shank motion. A key part of teaching stance technique has to become adjusting boot cuff for adequate shank range of motion. When I suggested to a student lessening cuff buckles, he reflexively tightened them. Ouch.

    Once the body finds (if boots permit it) the strong arch our neurology gravitates to your SR stance and presto all kinds of problems just go away including the back seat. Rather disconcerting it all has to be reprogramming after lunch.

    This brings me back to a general question of safety with respect to equipment. Not is the equipment safe? But safety in terms of how the brain perceives safety (balance) and makes purchase decisions. For example in skiing on one 190 cm ski and one 90 cm snowblade I notice that the 190 allows me to be way back without negative consequence. I had to really really learn to keep balance on the strong arch of the 90cm snowblade. In a hockey stop the 90 snowblade flew out form under me up into the air! I remained up right because of the other ski’s long tail and the hard stop of the other boot. My reptilian brain reaction to the short snowblade was it was unstable and therefore dangerous.

    The conclusion is when my brain tells me I was safe I will want to ski all day long in really bad form with boots/skies designed to compensate for, well, bad technique. Therefore neither would I likely ask other people to try the strong arch, SR, optimal range of motion cuffs, 90cm skies nor purchase lessons or equipment of like kind.

    No one I ski with is willing to try the 90/long ski combo or the pair of 90s. My guess is because of their emotional reaction to imagining loss of stability; their brains will NOT permit then to even try.

    These equipment usage and purchase decisions are occurring below the level of perception, consciousness. They are logical in terms of the reptilian brain’s safety hard wiring. I’m guessing this was the motivation for the student above to tighten (not loosen) boots because his brain equated more rigidity with safety.

    If we want to ski better read this blog don’t listen to your reptilian brain anymore. Except when the speed and accuracy of these emotional reactions saves your life!

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