ZEPPA-DELTA ANGLE AND THE STRETCH REFLEX


Never heard of the Stretch Reflex (SR)? You’re probably not alone. Even though the SR was the central focus of the research I did in 1991 with the Birdcage, I have yet to encounter anyone in skiing who knows what it is, let alone how it can function to assist skier balance by maintaining the major joint angles associated with a strong stance. The SR is what enables the world’s best skiers to ski with precision and with a fraction of the effort of lesser skiers.

After Nancy Greene Raine began supporting my work in 1978 and I started to work with world class racers and coaches I began to hear the comment that skiers like the legendary Toni Sailor or Nancy Green Raine ‘knew how to stand on their skis’. This implied that the reason other skiers could not ski like the Toni Sailors and Nancy Green Raines of the world was that they didn’t know how to stand on their skis. I found this puzzling. If it were that simple (it wasn’t and still isn’t), why hadn’t someone figured out how Sailor and Raine stood on their skis and started teaching the rest of the skiers how to stand the same way?

It was also about 1978 that the story began to take root within the ranks of the ski industry that ‘the foot functions best in skiing when it’s joints are completely immobilized in the ski boot’. The holy grail of skiing, a perfect fit of the ski boot that precisely mirrors the shape of a skier’s foot, emerged soon after. In this paradigm, if tight was good, tighter was better.

Aside from the obvious contradiction (the foot functions best when it is rendered dysfunctional?), it was a good story. On the surface, it made sense to most skiers, myself included, right up until I watched Nancy Green Raine undo all the buckles on her boots and ski better than any other skier on the hill. In observing and speaking with numerous elite skiers, a consistent pattern began to emerge; they all skied with their boots relatively loose compared to the boots of the average skier or racer; a stark contradiction to the ‘tighter is better’ story. A tight fit/loose fit paradox existed. This caused me to start to question the official position on boot fit.

By 1989, I had hypothesized that the SR was the ‘secret’ of the world’s best skiers. If I were right, these skiers weren’t flexing the shaft of their boots to put pressure on the front of the ski. They were flexing their ankles to set up the static preload that enables the SR. I had concluded that it wasn’t so much that elite skiers knew how to stand on their skis, but more a case that they were able to stand on their skis in a way that enabled them to use the SR. It seemed probable to me that these skiers had acquired a feel for the SR when they were first learning to ski. Once the feel was acquired, they were able to select boots and adjust them as required to enable the SR. The majority of skiers never acquire a feel for the SR when they first start to ski because the design and structure of their ski boots prevents this. If they don’t learn the feel of the SR early in skiing, the odds are great that they never will acquire it. If my hypothesis were correct, then the entire ski industry had gotten it wrong. The Birdcage experiments validated my hypothesis.

When Steve Podborski asked me to try and invent a new ski boot that did the same thing for all skiers as the in-boot technology I invented in 1980 did for him, I needed confirm my hypothesis that the structures of ski boots were preventing the majority of skiers from using the SR. This was especially important because preiminent safety experts had raised red flags in the Shoe in Sport (published in 1987) about the lack of sound principles in the design of the plastic ski boot. They had specifically flagged the shaft of the boot.

“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.”

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

A principle objective of my research in 1991 was to valid my hypothesis that structures of the ski boot prevent the overwhelming majority of skiers from being able to use the SR.

As far as I know, I am the first to describe how to set up the static preload that primes the SR and how to configure a ski boot so it accommodates and supports the SR. In the application of the SR to skiing, it is a powerful balance mediator and a PROTECTIVE mechanism.

The science behind the SR is complex. The best and perhaps simplest way to appreciate it is to acquire a feel for it by going through a static preload exercise barefoot on a hard, flat surface and then applying the acquired feel in progressive stages while standing in ski boots. This aspect involves correcting or removing any factors that prevent attaining the static preload. The process starts by learning how to set up a static preload on the shank-angle dorsiflexion angle.

  • In barefeet, stand erect on a hard, flat, level surface as show in the left hand figure in the graphic below.
  • Relax the major muscles in the back of the leg (mainly the hamstrings) and allow the knees to move forward as shown in the right hand figure.
  • As the knees move forward, the hips will drop down towards the floor. The ankle joint will dorsiflex and the angle of the shank with the floor and the angle of the knee will increase until a point is reached where the shank stops moving forward on its own.
  • As the knees are moving forward, bend slighly forward at the waist. The angles of the shank (ankles) and knees will decrease as the pelvis moves back and up and the back rounds. If you bounce up and down lightly, your stance will return to the static preload position.

static-preload

  • Move forward in the hips until you feel good pressure under the balls of your feet. Feel the whole system tighten up. You have set up a static preload on the shank of the leg. This is the foundation to build an SR stance on.

Try doing this in your everyday footwear. A number of factors  can prevent the setting up of the static preload that enables the SR. The ZeppaDelta Ramp Angle in ski equipment is a big factor as is drop in shoes. Over more than a few degrees of ramp angle, it is not possible for the SR to engage.

If you try the preceding exercise in your everyday shoes and the shoes have significant drop (toe lower than the heel), it is probably not possible to set up a static preload on your shank. Instead of stopping, the shank will keep going until it reaches the physiogical limits of ankle dorsiflexion.

In my next post, I will describe how to build an eccentric muscle contraction (EC) tensioned stance from the static preload shank angle.

 

9 comments

  1. Dear Dave,

    I like your blog and find it very informative – a quick question or two on how you are defining “static preload”.

    1) Am I understanding “static preload” they way you want us thinking of it? That is “static preload” is the basic optimal stance for skiing. This stance would be then modified to accommodate the forces and demands place on the skier’s body by speed, terrain, turn shape etc. In other words the body once it has learned this optimal stance(s) it will then use the stretch reflex to maintain optimal balance in the Coronal or frontal (for aft) and Sagittal (left right) planes regardless of terrain etc. It is this vital sensitivity element that allows as skier’s brain to actuality control the edge/snow interface to effortlessly locomote on skies.

    2) There is a caveat of course; the boot must be mechanically able to permit the optimal stance(s), or “static preload”.

    3) You are suggesting that the “static preload” be a learned experienced in bare feet so that the skier’s neurologic system will recognize the sensation both in skiing and boot fitting. Modern ski boots make both more difficult.

    So did I get the essence of the meaning of what you wanted us to know? Thanks for your dedication to learning, thomas

  2. David: An avid reader of your blog who is working at understanding it. I have implemented your plan on finding my resistive shank (RS) angle and stretch reflex (SR). I play with this every time I brush my teeth. What I feel when I do this is that first my calf (not sure which calf muscle) tightens and I can feel it working. If I lose my balance the core muscles will start contracting. After 2 minutes on one leg the calf starts getting sore. Just wondering if I’m going in the right direction??? I’m standing on a hard tile floor in bare feet and following your progression of standing naturally with weight on the heel, relaxing the ankle until pressure moves to the ball of the foot and maintaining thoughts balance and pressure there. Can’t wait to experiment with my new boots. First on list, make sure the forefoot is large enough to allow my foot to pronate, then make sure the shell doesn’t interfere with the natural function of my ankle, then do the same with the liner. The liner I’m using is a lange ZB with a liquid cork. Very thin liner with very little padding so I’m going to have to make some major changes in the shell to accomodate my ankle bones. Your thoughts please!

    1. Rick, the challenge in attemping to come at a well established frame of reference from a different perspective is that the established narrative is resistant to conflicting information because of what is termed ‘information bias/cognitive dissonance’. The challenge is made even greater by those with a financial interest in maintaining status quo who will try to discourage critical thinking because it can unsurp their position.

      In order to find a receptive audience for a paradigm like a ski stance based on eccentric muscle contraction and the stretch reflex, I have to try and find an opening that resonates with people. I tried to come at the SR static preload from several directions: load transfer? Nope, Reference Shank Angle? Nope. Resistive Shank Angle? A few hits, SR Static Preload? This might work. Getting a feel for the static preload is the first (pun intended) step to better skiing. Now I have to describe how to build a tensioned stance from the static preload shank position. It is not intuitive because it is not natural because………….. well, because skiing is not a natural activity. Working with elite ski pros and racers over the past few years has taught me a lot about the process to the point that I am now going to try and move forward in a logical progression instead of jumping all over the place.

      You’re headed in the right direction. But your efforts need fine tuning. I am going to try and write at least one post a week as winter is fast approaching and many would like to start their season on the right foot (or pehaps the left foot?) and especially stand the right way on their skis.

      “Can’t wait to experiment with my new boots. First on list, make sure the forefoot is large enough to allow my foot to pronate, then make sure the shell doesn’t interfere with the natural function of my ankle, then do the same with the liner. The liner I’m using is a lange ZB with a liquid cork. Very thin liner with very little padding so I’m going to have to make some major changes in the shell to accomodate my ankle bones. Your thoughts please!”

      Last ski season, I took on local Whistler-Blackcomb Ski Pro Matt. Matt is a big guy (225 lbs) with large boned feet. His physique is like a trim 5’10” male who has been enlarged to 6’3″. Matt sent me photos of his feet long before we met in person. So I knew (OK, I thought I knew) what I was in for. It took 2 pair of boots and about 5 liners to get his boots to the point where he could ski in them like he always thought he should be able to but couldn’t. Since he skis in race boots, the shells are smaller and narrower than recreational versions. The modifications were major. But the liners were a bigger challenge! Matt eventually found a pair of the old Lange fabric race liners.

      I will post on the modifications made to Matt’s boots after I finish the SR stance series. You have to learn stance outside your boots so you will know whether you can stand correctly in them and, if not, why. Start by expanding the shell. You need at least 3-4 mm clearance between boney tissues and the inner shell sidewall when standing in the shell on one foot.

      Hang in there. More coming soon.

      1. Thanks for your time David! I couldn’t agree with you more. The vested interests with “the perceived most to lose” will always try to discredit new ideas. In addition the ski industry is like a really big boat, it takes a lot of time and distance to change direction. Obviously those who are the elite skiers don’t need your help? but those of us who “know” something isn’t quite right are fertile grounds for your dissertations. ie Matt, Michael and I. I am a level 3 PSIA instructor teaching part time for the last two years after retiring from a career that started with instructing and ended with 20 years as President/GM of two different ski areas. I’ve made a lot of mistakes but I know you don’t move forward with anything if you “keep doing the same things over and over expecting different results”. Change is the only constant! My experience in observing and teaching beginners (most back seat skiers) making slow if any progress vs. those who have a “athletic stance” and make rapid progress, combined with your numerous discussion of drop, delta and net ramp angle and my playing with your exercises leads me to this theory. Why are their hips back? They don’t walk or stand like that. Correct me if I’m wrong, if I put a wedge under the heel, ie. increase drop or ramp angle etc., don’t your hips automatically move back so that you don’t fall on your nose?? What I’m saying here is that the industry is “begging for new skiers/riders” to replace the aging baby boomers, yet how many of those trying skiing are in the back seat, make slow if any progress and just give up because not being able to turn or stop at will is scary? Maybe that’s the audience you might want to work with??? I’m hoping to get into a position where I can test the above theory that reducing net ramp angle, moves the hips forward and will accelerate the beginner learning process. Your thoughts please!!! Thanks again for you input!!

      2. “Obviously those who are the elite skiers don’t need your help?”
        Actually, with very rare exceptions, skiers at every level can benefit because the process needs to be structured and evaluated at every step.

        “My experience in observing and teaching beginners (most back seat skiers) making slow if any progress vs…… Why are their hips back? They don’t walk or stand like that. Correct me if I’m wrong, if I put a wedge under the heel, ie. increase drop or ramp angle etc., don’t your hips automatically move back so that you don’t fall on your nose??”
        Absolutely. And the cause has been known for at least a hundred years. Contrary to what many in the ski industry believe, if you elevate the heel in relation to the forefoot you effectively reduce the contractile force in the muscles that keep you upright by effectively lengthening them. This makes the vertical column unstable. So the balance system responds by moving CoM back towards the heel where the mechanics are simpler. Have you ever seen anyone try to run in stilettos?

        “What I’m saying here is that the industry is “begging for new skiers/riders” to replace the aging baby boomers, yet how many of those trying skiing are in the back seat, make slow if any progress and just give up because not being able to turn or stop at will is scary? Maybe that’s the audience you might want to work with???”

        Andy Bigford, former editor of Snow Country called it in a hard hitting editorial in 1991; the corporatization of skiing was going to eliminate the passionate skiers and replace them with drones who only need to be competent enough to make it to the village so they can max out their credit cards in the corporate owned stores and restaurants. I moved away from Whistler from 2005 and returned in 2012. The first thing that hit me the first day I went skiing was how badly everyone skis, especially the ski pros. It was so bad, it made my eyes bleed. I got the inside word that corporations don’t want pros to actually teach skiing because if it seems too hard, it will quench the appetite of their ‘clients’ to spend, spend, spend. So the ski schools have been told to dumb it waaaaay down. Even most ski pros today ski like drones with a poker stuck up their ass.

        I am going to fast forward the SR stance posts and then provide the details later. This should help skiers like yourself make the jump to a higher level of fun with minimal effort; the most for the least. I am counting on skiers like you to go forth and become disciples of the Skier’s Manifesto.

      3. Thank you David! I am not one of those “corporate”guys! I can describe the first day on skis when I was 3 years old. Still love it and bring that passion to teaching skiing. Unfortunately I was not invited back to teach, not because I wasn’t a good instructor, but because “I didn’t fit in!” Well when you are looking for solutions and not respecting commonly held beliefs thats what happens. Please keep doing what you are doing! I’m sure it will take awhile but there are more people like you and me that seek “the truth” without getting hung up on our own beliefs. Hope I can help!

  3. Hi David
    Is your SR felt in the calves or does it include the torso and shoulders as well?

    1. Yes. The tension starts in the arches of the feet, bridges to the calve muscle (soleus-gastroc) and extends through the hams, traps and lats all the way to the shoulders which must be rounded and pulled forward. The starting point is to set up the static preload in the soleus then move up the chain from there. A key piece of information that has prevented the recognition of the SR is that skiers-racers flex their boots during a turn. Anyone with a basic knowledge of functional anatomy would know that this is both physically impossible and undesriable because it would require a decrease in the contractive force of the calve muscles.

      I will be posting at least once a week from now on to get to the SR stance subject completed.

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