Zeppa-Delta Angle posts

IS SHIFFRIN ON THE LEVEL?

By on the level, I am suggesting that Shiffrin may have a much lower zeppa-delta ramp angle than her competition.

Here are some screen shots from the March 18, 2018 Are Slalom where Shiffrin won by  1.58 seconds. She is on and off her edges in milliseconds as she just seems to pop from turn to turn – Total Domination From Shiffrin (1.)

Compare the angles of Shiffrin’s ankle, knee and hip in the photo below to those of her competition in the second and third photos below.

Notice how extended Shiffrin’s lower body is as she exits the rise line and enters the bottom of the turn in the photo below from a training session earlier in the year.

Extended in the Are Slalom.

Out of the start her knees and ankles are almost straight!

In my next post I will explain what I think is happening and why.


  1. https://youtu.be/gQu-LkyfsRQ?list=PLo6mlcgIm9mzWPBpeXnH2CpFOXrWhBiEB

RAMPING UP THE POWER OF YOUR STANCE

Note to the reader

The post that follows was originally published on March 1, 2016. At the time that I wrote it, I was trying to identify the optimal net (total) ramp angle or NRA using fixed angle ramps. But I found the process to be inconclusive for reasons I give in my recent posts on the dynamic ramp assessment device. I am reposting this older post because many of the concepts expressed are even more relevant in view of the results seen with the dynamic ramp assessment device and boot boards altered to the same ramp angle identified in dynamic testing.


RAMPING UP THE POWER OF YOUR STANCE

The foundation of a strong technique is a strong stance. But what makes a strong stance? The angle of the combined ramps of the binding and boot board or zeppa in relation to the base of the ski. If the net ramp angle weren’t important, binding and boot makers would make their products with no ramp. If ramp angle doesn’t make a difference, why bother? But not only does net ramp angle make a difference, it has a significant effect on stance.  Stance affects balance and muscle power, especially the ability of eccentric gastrocnemius-soleus complex muscle contraction to absorb shocks that would otherwise be transmitted up the leg to the knees and back. I discussed some of these issues in WHAT’S YOUR ANGLE? – : https://skimoves.me/2014/03/29/ski-boots-whats-your-angle/ ‎

If there were a problem, and there is, the ski industry is all over the place especially when in comes to binding ramp. There doesn’t appear to be any industry standards and especially any continuity between products. Worse, most skiers assume that their ski boots are putting them in the optimal stance. Without a reference they have no way of knowing. The Stance Ramp can give them that reference especially when it comes to how much ramp is enough, how much ramp is too much and how much ramp is too little.

Note Added March 19, 2018 – Having a kinesthetic sense of a stance based on tensegrity gives a skier a valuable tool that when used in a structured process can help them assess the effect of zeppa-delta ramp angle and the constraint imposed on their feet and legs by the structures of a ski boot.

In 1978, when I was building boots for female racers with small feet, I noticed that they were skiing like they were wearing high heel shoes. When I started checking their bindings and boot board ramps, I found out why. Some had 10 or 12 degrees or more of net ramp angle. After I started doing stance training with racers on a ramped board I discovered through empirical experiments that about 3 degrees of ramp angle seemed to give skiers the strongest stance.

Note Added March 19, 2018 – It now appears as if 3 degrees is the upper limit of the zone of stability. This explains why skiers started to ski better when the net ramp angle approached 3 degrees.

I didn’t really understand why until much later. Was the process scientific? No, not at all. Do studies of this critical issue need to be done? Absolutely. If I figured out that ramp angle was a critical issue almost 40 years ago, why is it that no studies appear to have done in the intervening years to determine the affects of ramp angle and identity the optimal angle?

With input from skiers in different parts of the world over the past two years, I have narrowed the ideal ramp angle down to about 2.7 degrees. This seems to be something of a standard in World Cup. Through experiments over the past few months, I have found that changes of 0.1 degrees can make a significant and easily perceivable difference. Optimal ramp angle isn’t just critical for World Cup racers, it is critical for all skiers. The easiest way to convince yourself of the importance of optimal ramp angle is for you to experience the effects of ramp angle through experimentation. How? With a Stance Ramp set to a base reference angle of 2.5 degrees.

The Stance Ramp lets skiers stand in their ski stance (barefoot is best) on a flat, level, surface then assume the same stance on the Stance Ramp, compare the kinaesthetic sense and judge whether they feel stronger of weaker. The angle of the Stance Ramp can be predictably increased or decreased by inserting shims at either end between the ramp and the surface it is supported on. When the ramp angle that makes the stance feel the strongest is arrived at, it can compared to the ramp angle of the ski boot board by having one foot on the Stance Ramp and the other in the ski boot.

The best part? The Stance Ramp is easy and inexpensive to make with readily available materials. I made mine out of some scraps of plywood I had lying around. Here’s what the Stance Ramp I made looks like. You stand with one foot on either side of the stiffener in the center with your heels at the high end (left end in the photo below).

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Here’s a top (plan) view. It is a good idea to check the surface the ramp will sit on to make sure it is very close to level.

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Here’s the underside of the Stance Ramp showing the element at the rear that gives the ramp its 2.5 degree angle. The stiffener in the center is important to ensure the ramp doesn’t flex under your weight.

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The sketch below is a basic plan for a Stance Ramp. The only critical details are the height or thickness of the element that lifts the rear aspect of the ramp to achieve and 2.5 degree angle (angle A) and the distance the lift element is placed from the front edge of the ramp. The stiffening element in the center of my ramp is 8 cm wide. The ramp has to be big enough to stand with the feet under the hips and long enough to accommodate the length of the feet.

Stance Ramp

An online right angle calculator such as the one at cleavebooks.co.uk can be used to calculate the spacing of the lift element from the low end (front edge) of the ramp based on its thickness.

SR calculate

Once the optimal ramp angle is arrived at, the Stance Ramp can be used in combination with the ski boot shell to confirm that the boot board is at the same angle.

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In my next post, I will discuss what I call the Resistive Shank Angle that is the base to build  a strong stance on.

WHY STANCE TRAINING IS ESSENTIAL

When readers click on my blog address at skimoves.me, analytics give me a hierarchy of the countries with the most views and the most popular posts in ascending order. This helps me identify which content resonates most strongly with viewers and which content draws a blank.

As I write this post, the top five countries are the US followed by Croatia, the United Kingdom, Slovakia and France.

The most viewed post today is THE SHOCKING TRUTH ABOUT POWER STRAPS; far and away the most popular post I have published to date. But the most important posts by far that I have ever written, A DEVICE TO DETERMINE OPTIMAL PERSONAL RAMP ANGLE and STANCE MUSCLE TENSIONING SEQUENCE EXERCISE barely sputtered in comparison. This strongly suggests that far from just some small gaps in the knowledge base skiing is founded on, massive craters exist.

Arguably the most important aspect of skiing is a strong stance. Any variance in the fore-aft angle of  the plane of support under the feet and the plane of the base of the ski has significant impact on stance. Yet these subjects are barely blips on the Doppler Radar of the ski industry.

Since I started the dynamic ramp angle assessment project a few weeks ago I have found that when asked to do so, it is rare for a skier of any ability to be able to assume a strong ski stance in an off the ski hill environment. Even when a skier  skis with a relatively strong stance, they seem to lack a sense of what a strong stance feels like. Because of this, they lack the ability to consciously replicate a strong stance. If asked to do so, they would be unable to coach a skier in the sequence of events that I described in my last post

In the dynamic ramp angle assessment project, I  have also observed that skiers with with a boot/binding ramp angle greater than 2.8 degrees appear to have become accustomed to the associated unstable, dysfunctional feeling and identify with it as ‘normal’. Before I can test them, I have to spend time coaching them into the correct stance because it feels unnatural to them.

When I go back and forth between a strong functional stance on a flat, hard level surface to a stance on the dynamic ramp angle device set to an angle of 4 degrees, I can get close to the same angles of ankle, knee and hip. But when I do, I feel strong tension, stiffness and even pain in my mid to lower back which is  common in some skiers and even racers.

Based on results to date with the dynamic ramp angle device, it appears as if strong skiers ski best with ramp angles close to zero. But depending on their sense of balance and athletic ability, they may have a wide range in which they sense little difference on the effect of ramp angle until they approach the upper limit of stability. While they may be able to ski well with a ramp angle close to the maximum limit of stability, ramp angles much above 1.2 to 1.5 degrees may not offer any benefits. This can only be tested on skis where balance is tested by dynamic forces which cannot be replicated in a static setting.

Issues affecting skier stance were discussed in detail in my post, THE SHOCKING TRUTH ABOUT POWER STRAPS. Here are the excerpts I posted from the chapter on The Ski Boot in the book, The Shoe in Sport (1989), published in German in 1987 as Der Schuh Im Sport– ISNB 0-8151-7814-X

“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”. – Biomechanical Considerations of the Ski Boot (Alpine) – Dr. E. Stussi,  Member of GOTS – Chief of Biomechanical Laboratory ETH, Zurich, Switzerland

“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., (14 degrees) 20 to 22 degrees. Up to that point, the normal, physiologic function of the ankle should not be impeded”.

“Previous misconceptions concerning its 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.

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

It has been over 40 years since international authorities on sports science and safety raised red flags concerning the adverse effects of ski boots design and construction on skier stance, balance and the potential to cause or contribute to injury. It is time that their concerns were taken seriously and acted on. Research on stance and the effect of such things as zeppa and delta ramp angles is urgently needed.

 

FIFTH GENERATION STANCE RAMP ASSESSMENT DEVICE

Since my first version of the stance ramp assessment device I have made a number of significant improvements. The series of photos below are of the fifth generation device.

The bottom plate or base of the device is approximately 18 inches (46 cm) wide by 16 inches (41 cm) deep (front to back). I intend to make the next version about 22 inches (56 cm) wide by 18 inches (46 cm) deep. Size is not critical so long as the top plate is deep and wide enough for the feet being tested.

Stiffness of the plates is critical. Three quarter inch thick (2 cm) plywood or medium density fiberboard (MDF) are suitable materials. I added 1.5 inch x 1.5 inch wood reinforcing ribs on the sides, middle and rear of the top plate.

The photo below shows the heel end of the device. Two 1/4 inch drive ratchets turn bolts threaded into T-nuts in the top plate that raise the heel end up.

The photo below shows the top plate hinged to the bottom plate with 4 robust hinges.

Four telescoping hard nylon feet are set into the bottom plate to enable the device to be leveled and made stable on the supporting surface. It is important that the device not tilt or rock during testing.

The photo below shows the details of the interface between the top plate on the left and the bottom plate on the right.IMG_3409

I used gasket material purchased from an auto supply to shim the forefoot of my boot boards to decrease the ramp angle so as to obtain the 1.2 degree ramp angle I tested best at.Shim pack

The package contains 4 sheets of gasket material that includes 3 mm and 1.5 mm sheet cork and 2 other materials.Gasket

I cut forefoot shims from the 3 mm cork sheet as shown to the right of the boot board in the photo below.BB w shims

I adhered the shims to the boot board with heavy duty 2-sided tape and feathered the edges with a belt sander.shims installed

I corrected the ramp of my boot boards in 3 stages. Once my optimal ramp angle is confirmed, I will pour a boot board into the base of my ski boot shells in place of the existing boot boards using a material such as Smooth-Cast 385 Mineral Filled Casting Resin. More on this in a future post.

Ramp Angle Appears to User Specific

It is important to stress that although there appears to be a trend to optimal boot board ramp angles for elite skiers in the range 1.5 degrees or less, there is no basis to assume a  ramp angle that is optimal for one skier will be optimal for another skier. Recreational skiers are testing best between 2.0 and 2.5 degrees.

It is also not known at this point whether the initial optimal ramp angle identified with the device will change over time. Based on the impressive results seen so far in the limited number of skiers and racers who were tested and ramp angles adjusted there is no basis to assume that ramp angle is not a critical factor affecting skier balance and ski and edge control. Studies on this issue are urgently needed and long overdue.

It is important that testing for optimal ramp angle be preceded by kinesthetic stance training. This will be the subject of my next post.

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.

 

MORE ON ZEPPA (BOOT BOARD) RAMP ANGLE

Slowly, but definitely, the ski community are learning the positive boot board (zeppa) ramp in many boots is excessive and not beneficial to many of us. Excessive seems to be anything over approximately 3.0 degrees. The lowest ramp I have measured to date was 2.4 degrees in the latest Dalbello DRS boot in a Mondo 27. A size 23 is still over three degrees.

I believe most manufacturers have too much ramp in their boots. As explained in a recent post, the problem is worse for smaller boots, since as boots shorten, ramp increases. Still, even if boot ramp is correct, we should wonder if binding designers think boot designers need some design help, since nearly all bindings have positive ramp (delta) of at least a few degrees for Mondo 27 boots.

Like boot zeppas, as binding toe and heel are mounted closer together, delta increases and is additive with boot ramp. Further, there are additional changes to boot angle since binding delta tilts the entire boot, It also alters effective forward lean.

I believe when we demo skis, a portion and perhaps a substantial portion, of the differences we feel between skis, may be accounted for by the differences between ski binding ramp angles. At the very least, binding angles can corrupt on-snow testing of skis and/or boots. If you are working to get your boot setup perfectly adjusted to your preferences, why allow binding ramp variables to alter an optimal configuration?

In my opinion, the best solution is a 0 degree binding delta. If this is not achievable, at least set all skis bindings to the same delta. This may be easily, achievable. Most manufacturers make shim kits for at least some of their bindings. Shims appear to be available for most bindings used on race skis that allow incremental changes to 0 degrees delta. However, not all shops know of the existence of these shims since  kits are usually in the race catalogue, not the recreational product catalogue.

If alterations to either binding heel or toe height are made, an equal change must be made to screw length or there will definitely be an unsafe situation. Binding holes are between 8.5 and 9.0mm deep. Be certain screw threads do not extend more than that amount from the bottom of the binding.

One last thing to remember is that moving binding position forward or backward on the ski could subtly alter binding delta since the top surface of skis are crowned. Moving the bindings to a new position on the crown will affect the height of the heel and toe. If bindings are moved after setting binding delta, it should be checked again.

I always prefer to direct measure rather than use a calliper and calculate zeppa or delta. The photos below show a device I had fabricated that allows the angle of a zeppa to be measured between the two primary load points under the heel and the head of the first metatarsa (aka ball of the foot). The distance between the rods can be adjusted to these two points on a zeppa or to the 2 points of contact of a boot sole on the heel and toe pieces of a binding.

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The SmartTool digital level shown in the photo below accurately reads to one decimal place.

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The SmartLevel is too long to sit properly on a zeppa. The two rods of the frame that supports the level lets me avoid toe kick or any other shapes that can distort ramp angle.  I just measure the angle directly between the two points of support.


Lou Rosenfeld has an MSc. in Mechanical Engineering with Specialization in Biomechanics earned at the University of Calgary Human Performance Laboratory. His research was titled, “Are Foot Orthotic Caused Gait Changes Permanent”.

While at HPL, he assisted with research on the effects of binding position for Atomic, and later conducted research for Nordica that compared Campbell Balancer established binding position to the Nordica factory recommended binding position.

Lou is one of the invited boot-fitters on the EpicSki forum “Ask the Boot Guys” and has authored articles on boot fit, balance, alignment and binding position for Ski Canada, Ski PressSuper G, Calgary Herald, and Ski Racing, USA. He is a CSIA Level 2 instructor and CSCF Level 1 coach. He currently resides in Calgary where he owns and operates Lou’s Performance Centre. A selection of his articles may be found at www.Lous.ca.

 

A FOLLOWER OF THE SKIER’S MANIFESTO COMMENTS ON BOOT BOARD/BINDING RAMP ANGLE

The universal boot truisms that David puts forth in his blog is a ‘blueprint’, ‘computer program’, what ever you want to call it which is applied on an INDIVIDUAL basis. Each individual is measured with the system and then the results are applied to the boot. Unlike ‘one boot fits all skiers’ which is the current system the industry provides. I can’t believe that anyone would buy a boot based on a ski magazine test but that probably is hardly worse than the info one gets in the ski shop which gave me nerve damage in my feet (gratefully healed now since I gave up on ‘race fit’). David talks about using flat shims of varying thicknesses to fine tune ramp angle just like canting shims or duct tape are used for lateral experimentation; 2.5-6 is his starting point while I would start with zero but with current ski bindings only millimeters of fine tuning can be done when some individuals need centimeters from the current setups. Obviously if one changes the ramp angle the shank angle may have to be adjusted also which is why skiing is believing, David gives a perfect example in his reply on what lower ramp angle did for his skiing. Also the extremely high starting point on ramp angle makes it impossible for many skiers to loosen their cuff for normal forward flex because they need to be clamped tight to prevent falling one their noses; that’s where I got fooled for a couple of decades.

Having built an adjustable plate for ramp/delta in the early 2000s I can tell you one thing for sure; the skier knows instantly if things are better or worse. That by no means indicates an optimum net ramp because there are so many other aspects of the boot that are factors such as toe crunch (race fit) and ankle flex restricted to virtually zero. I started from the wrong end with ramp/delta whereas David starts in the boot first which is what I would do but took me about a decade to loosen my boot cuff significantly enough to make a difference; that due to a hip joint that was killing me from skiing. 2 months after loosening the boot cuff and removing the power strap which is only good for carrying the boots (my opinion), I was introduced to The Skier’s Manifesto and learned from that how to create an ankle glide path, free the toes, free the arches, etc. What amazes me is 2 things; first that when I first decided to build the BalancEnhancer as I call it (due to a friend’s prodding), that it actually worked , and second, how hard it is to even get skiers to try something different and the number that do try it and then don’t even try to modify their own equipment to their needs based on what had made there skiing better!!

  • Michael Pupko