Zeppa-Delta Angle posts

BOOT BOARD STANDARD: A PROPOSED STARTING POINT

At the time that I designed the Birdcage research vehicle in 1991 with a biomedical engineer, I was aware that a Net Ramp Angle (boot board + binding ramp) of more 3 degrees had a significant, perceivable, negative effect on skier stance and balance. Although I didn’t know what the range of the optimal Net Ramp Angle was (and still don’t), I knew that Net Ramp Angle is affected by the length of the Achilles tendon and that this aspect affects the synchronizing of peak arch tension with peak Achilles tendon tension that occurs just before the heel separates from the ground to initiate propulsion. I refer to this as the Reference Shank Angle. It is the foundation on which to build a strong stance from the bottom up.

Since my experience prior to 1991 had demonstrated that more than 3 degrees of Net Ramp Angle was too much, a decision was made to fix the Net Ramp Angle of the base of the small Birdcage, shown below, at 2.5 degrees and the base of the large Birdcage at 2.35 degrees.

Screen Shot 2016-08-09 at 3.30.12 PM

The small Birdcage fit US men’s size 4 to 8 feet. The large Birdcage fit US men’s size 8 to 12 feet. Thus, all skiers with feet in a Birdcage size range had the same Net Ramp Angle.

Since the base of the Birdcage acted as the boot board, there was no removable boot board as in most ski boots. The base shown above was made from high grade aluminum and was in the order of many times stiffer and more torsionally rigid than was necessary to withstand the expected loads of skiing without deforming. This is an important factor that will be discussed in a future post.

Since 1978, I had suspected that the plastic shells of most, if not all, conventional ski boots were undergoing significant deformation under loads typically of racing. So I began stiffening the bottoms of ski boot shells with a torsion box structure similar to those used to stiffen skis. Recent studies have not only confirmed my suspicions, but shown that the deformation that occurs can be far worse than I suspected. Consistent with good practices of science-based research the entire Birdcage was engineered with excess structural capacity so as to ensure that it could easily withstand the maximum loads imposed on it without significant deformation as this could disrupt the processes of skier balance and control.

An important aspect of the Birdcage was continuity of the surface structure that the foot rests on. A one piece top sheet comprised of 5 mm thick high grade aluminum formed into a tub was secured to the base with screw fixations. The 3 black strain gauges shown mounted on the base (2) and side plate (1) in the photo below of a left foot Birdcage show the continuity of the surface under the balls of the feet. Continuity of the surface under the ball of the large toe is especially critical.

IMG_6453

In order to ensure each test skier was as close as possible to the Reference Shank Angle, the start and end points of shaft rotation and the forward end point at which resistance was introduced were adjusted to peak Achilles tension – Shank Reference Angle so as to make the effect of ramp angle as consistent and neutral as possible without fine tuning it to each test skier.

The photo below shows the rotation resistance control mechanism on the back of the Birdcage.

IMG_6451

This important aspect is discussed in detail in US Patent No. 5,265,350. FIG 56 below from the patent, shows the means to adjust the rearward travel limiter of the shaft to set the shaft forward lean angle, forward travel limiter of the shaft to set the limits of forward shank movement and journal resistance means for 10 to 12 degrees of low resistance shaft rotation.

Fig 56

A reasonable starting point for a boot board standard would include the following:

  • A ramp angle of 2.5 degrees with a  shim kit with 0.1 degree shims for the heel and forefoot to facilitate fine tuning based on ski testing.
  • A top plate surface that the foot rests on that is monoplanar (flat in the long and transverse planes) with the transverse plane parallel to the transverse aspect of the base of the ski.
  • Torsional qualities that when integrated with base of the boot shell maintain deformation of the boot board and boot shell base within agreed upon acceptable limits.
  • A top plate surface that the foot rests on that is contiguous under the heel and the balls of the feet, especially under the ball of the big toe under the the 5th metatarsal.

THE BOOT BOARD FACTOR

While the Ottawa researchers did not explore this aspect, they correctly identified that equipment, including custom insoles, technical skills and ski technique might explain why the pressures recorded under the heel and the head of the first metatarsal of some instructors were much higher than the pressures seen in the same locations in other instructors.  The University of Ottawa studies are the only ones I am aware where the researchers considered the effect  of what is known in research as uncontrolled variables on their findings. Poor technique and interference with the function of the foot and leg caused by the ski boot can ensure that COP remains under the heel.

Although boot board ramp angle and shape have an undeniable impact on the function of the feet and lower limbs, as evidenced by the photographs below of a sampling of boot boards, there does not appear to be any continuity, let alone any standard for boot board ramp angle and the form of the surface that interfaces with the sole of the foot.

1

 

2

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3

IMG_6187

4

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When the effect of  binding ramp angle, which appears to have even more variation than boot board ramp angle, is added to ramp angle equation to arrive at Net Ramp Angle, the possible combinations that make up Net Ramp Angles becomes unlimited and can range from as little as two to as much as ten degrees.

As if the lack of any apparent standard for boot board and binding ramp angles were not causing enough of an impact on skier/racer performance, there is a factor that appears to be compounding the issue by introducing a layer of inconsistency; boot base shell deformation under loads typical of recreational skiing.

I will discuss boot base shell  deformation in a future post. In my next post I will propose a starting point for a boot board standard.

STANCE KILLER: EXCESSIVE RAMP ANGLE

Ramp sole angle or drop, as it is called when the heel is elevated above the forefoot in footwear, affects the function of not just the foot, but the entire muscle-skeletal and balance systems.

With few, exceptions, the sole structure of most shoes elevates the heel above the forefoot. Prolonged activity in footwear with anything other than minimal drop will result in chronic contraction and shortening of the muscles in the backs of the lower leg.

“This is an extremely serious situation considering the fact that the shortened lower leg muscles are now contributing to faulty foot function in a number of ways. The most significant foot fault caused by elevated heels is that shortened posterior leg muscles pull improperly on the back of the heel (Achilles tendon) to unnaturally increase the amount of flattening the arch will undergo. Said another way, chronically shortened lower leg muscles increase pronation of the foot and ankle.

“A more significant and potentially debilitating effect of heel elevation is that there is an involuntary stretch reflex built into the posterior lower leg, that can only be activated if the heel is allowed to come close to the ground. This does not occur in most shoes available to consumers today, EVEN amongst athletic models”. – Northwest Foot & Ankle (nwfootankle.com)

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“Barefoot, the perpendicular line of the straight body column creates a ninety degree angle with the floor. On a two-inch heel, were the body a rigid column and forced to tilt forward, the angle would be reduced to seventy degrees, and to fifty-five degrees on a three-inch heel. Thus, for the body to maintain an erect position, a whole series of joint adjustments (ankle, knee, hip, spine, head) are required to regain and retain the erect stance.

“In this reflex adjustment scores of body parts — bones, ligaments and joints, muscles and tendons — head to foot must instantly change position.

“But shoe heels have other, lesser-known influences on gait. For example, any heel, low to high, requires a compensatory alteration or forward slant on the last, which is translated to the shoe. This slant is known as the “heel wedge angle.” This is the slope or slant of the heel seat, rear to front, to compensate for the shoe heel height. The higher the heel, the greater the angle.

“On the bare foot there is no wedge angle. The bottom of the heel is on a level one hundred and eighty degrees, with body weight shared equally between heel and ball. Inside the heeled shoe, the wedge angle shifts body weight forward so that on a low heel body weight is shared forty percent heel, sixty percent ball; and on a high heel ninety percent ball and ten percent heel.

“Let’s add one further influence of shoe heels, low to high. The shoe’s elevated heel shortens the Achilles tendon and accompanying shortening of the calf muscles.”  – Dr William A. Rossi, DPM. ‘Why Shoes Make ‘Normal’ Gait Impossible’ – Podiatry Management. March 1999.

Katy Bownman also talks extensively about the adverse effects of heel lift in her book Whole Body Barefoot: Transitioning Well to Minimal Footwear.

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The reason I started this blog on May 11, 2013 with my first post, A Cinderella Story: The ‘Myth’ of the Perfect Fit – https://skimoves.me/2013/05/11/the-myth-of-the-…sive-perfect-fit/, was because a number of issues in my mind were still nebulous. Even though my boot modification efforts over several decades had consistently met with success at the highest levels of Olympic and World Cup competition, I still had more questions than answers. I knew that I was close. But I did not yet have the big picture figured out. One question that remained unanswered was, is it possible to develop a formula for setting up the boot/binding/ski system that will consistently maximise skier/racer performance? One thing I was certain was critical to any formula is the angle of the ramp the skier stands on in relation to the surface of the snow under the base of the ski.

Since 1978, I had known that a combined ski boot boot board/binding ramp angle (Net Ramp Angle) of about 3 degrees was critical to the development of a strong stance and that the positive effects of ramp angle fell off dramatically at NRAs of more than 3 degrees. I had a hunch that less NRA than 3 degrees allowed a stronger stance. But I didn’t know the NRA optimal range and especially where the bottom end was at which NRA became too low.

When I designed the Birdcage in 1991 with a biomedical engineer, we made two sizes. The small size fit US men’s 4 to 8 feet. The base ramp angle was 2.5 degrees. The large size fit US men’s size 8 to 12 feet. The base ramp angle  2.35 degrees. The ramp angles were based on our theory that it was better to be on the low side of optimal than on the high side. We were hedging our bets by playing what we thought were the low and high ends of the optimal range with 2.35 and 2.50 degree ramp angles. The robust adjustment range of the Birdcage made it possible for skiers with up to size 8 US men’s feet to ski in both the small and large versions. This made it possible for some testers to compare the 2 different ramp angles.

For those of you who are not familiar with the Birdcage experiments, the links below are to 4 posts on the Birdcage in the order of first to last.

EPICSKI ARTICLE – THE BIRDCAGE EXPERIMENTS

https://skimoves.me/2014/03/03/epicski-article-…cage-experiments/

THE BIRDCAGE DATA – WORLD PREMIER

https://skimoves.me/2014/03/03/the-birdcage-data-world-premier/

THE BIRDCAGE EXPERIMENTS – DATA 3

https://skimoves.me/2014/03/05/the-birdcage-experiments-data-3/

BIRDCAGE VS. CONVENTIONAL

https://skimoves.me/2014/03/07/birdcage-vs-conventional/

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The Effect of Heel Lift or Ramp

Elevating the heel above the forefoot more than a small amount, tips the whole body forward. This provokes a compensatory balance response that alters the default angles of the ankle, knee and hip joints and the lengths of the associated muscles. This can dramatically affect the functional integrity of the foot and compromise the effectiveness of the balance system. That elevating the heel affects everyone in this manner is a virtual certainty.

Past a certain point, NRA in the stack of ski equipment between the sole of the foot and the surface of the snow will force a skier to retreat to weight borne on the heel with support for the leg from the rear of the boot shaft for stability.

After a lot of experimentation last season and input from reliable sources  in Europe I reached a tentative conclusion that the optimal Net Ramp Angle is in a range between 2.5 to 2.7 degrees. But nothing is really ever settled. A complicating factor is wearing shoes with varying degrees of drop. This prevents the balance system from using the default barefoot, zero drop balance reference or developing a consistent balance reference based on a fixed drop. Further exacberbating the effect of Net Ramp Angle is that boot boards are seldom monoplanar (dead flat in the x – y planes.

In my next post I will discuss the factors that add to and complicate the effects of Net Ramp Angle and my vision for a standard boot board ramp that would serve a ski stance/balance reference and a starting point for Net Ramp Angle Optimization.

 

RAMP ANGLE RESONATES

My recent series of posts on the effect of ramp angle on stance seems to have piqued interest in this subject. The two posts with most views in recent weeks are:

  • #1 – RAMPING UP THE POWER OF YOUR STANCE and
  • #2 – STANCE BASICS 101; RESISTIVE SHANK ANGLE

The following postS were close behind,

  • STANCE BASICS 101: ECCENTRIC MUSCLE POWER
  • STANCE BASICS 101; RAMP ANGLE TIPPING POINT
  • SKI BOOTS: WHAT’S YOUR ANGLE
  • CALCULATING RAMP ANGLE
  • THE SHOCKING TRUTH ABOUT POWER STRAPS

Since I first raised the issue of net or compound ramp angle on June 2, 2013 in my post , Ski Racing: An Unlevel Playing Field, I started to look critically at ramp angle, especially the net or compound ramp angle. This includes the contribution of ramp angle from boot boards and bindings. In past year, in working closely with skiers in other parts of the world, including a racer in Europe who I work with on an almost daily basis where the effect of every change is carefully evaluated  and documented on video, I have tentatively concluded that ramp angle may be the single most important factor affecting skier balance and control of the skis.

In my post,  SKI RACING: AN UNLEVEL PLAYING FIELD, I said of my work back in 1977,

“But I was adjusting two other things that no one even seemed to even be aware were issues; net ramp angle and position of the ball of the foot and big toe in relation to the ski edge underfoot.”

I went on the explain,

“Net ramp angle is the inclination of the sole of the foot in relation to the surface of the snow. It affects the muscles a racer can use and especially the ability to apply force to the fore body of a ski and the ability to activate what I call the auto processes of edge control and turning forces. Two factors contribute to forward inclination; 1) the ramp angle of the boot board that the sole of the foot is supported on and , 2) the angle created by the heel and toe plates of the ski binding. I don’t know where they are today, but back in 1977 ramp angles were all over the map in both boot and binding brands and even models. Because of this, both the base angle of the boot sole plate and binding had to be considered as a unit in determining net ramp angle. Although few if any were aware of this issue, to me it explained why a racer’s skiing and results sometimes went downhill when they changed to a different ski binding or boot or worse, changed both.”

Ramp Angle Roulette

If I thought that ramp angle was all over the map back in 1977, the situation is infinitely worse today. Back in 1977, there were a limited number of bindings on the market. Today it seems as if the sky is the limit.

A few weeks ago, a recreational skier who was having problems with their boots and skiing asked me for my assistance. It quickly became obvious that the boots, which had no modification, were far too tight and especially too narrow for the skier’s wide peasant feet and squared off toes. When I checked ramp angles, the boot board was 3.27 degrees and not monoplanar (not flat). The ramp of the bindings was 1.90 degrees as set for the length of the boots. The net ramp angle was 5.17 degrees.

Adjusting the ramp angle of the boot board was not possible because it was an injected plastic form that is not easily modified. Since new boots were needed, I made sure that the ramp angle of the boot board could be modified. Bindings were another matter entirely. When I started what became an extensive and exhaustive search for a recreational binding with zero ramp, I could find none. Worse, when I started to check bindings for height differences in the toe and heel piece platforms, I could find no consistency, let alone even a hint of any sign of any standard. They all seemed to be different. Since modifying bindings is not an option, at this point I am at an impasse with no solution to offer the skier.

The KIS Principle 

The goto mantra of the ski industry is the KIS principle; Keep It Simple. I fully subscribe to this principle which is why my efforts are directed at creating an environment in the ski equipment system, especially in the ski boot, that supports optimal human performance and balance. From a perspective of balance, skiing is one of the most complex activities we engage in. The ski amounts to perturbation platform in motion over undulating terrain with different coefficients of friction in a dynamic, constantly changing 3-dimensional physical environment. The wide variances between ramp angles in ski boots and bindings and the fact that the ramp angle contribution from bindings is variable according to the boot sole length, make the combination of net ramp angles both unpredictable and almost unlimited. When I  noted back in 1977 that the lack of any apparent standards, “explained why a racer’s skiing and results sometimes went downhill when they changed to a different ski binding or boot or worse, changed both”, the situation is far worse today. How many careers of promising racer’s have been compromised because the effect of ramp angle was not appreciated?

The Question

There are two possibilities.

  1. Ramp angle has no significant effect on skier function, especially balance, in which case the standard should be zero boot board and binding ramp, or
  2. Ramp angle has a profound effect on skier function, especially balance, in which case studies should be done to ascertain the effects of ramp angle and especially a method by which to determine individual ramp angles for optimal function and balance.

If it turns out that ramp angle is as critical as my recent experiences and subjective experiments are suggesting, then the current state of the unlimited possible ramp variances skiers are presented with is the antithesis of the KIS principle when it comes to making skiing easy and enjoyable.

This brings us to the question, is ramp angle critical or irrelevant?

  • If ramp angle is irrelevant, why is it present in boots and bindings?
  • If ramp angle is critical, how can it be variable with no consistency in application?

In my next post, Michael who has been applying material from my blog will relate his experiences in his own words.

 

 

 

 

SR STANCE BASICS: RAMP ANGLE TIPPING POINT

If you have made a Stance Ramp or are planning to make one, it is important to use stiff material for the platform you stand on. This especially important if you are heavy. If you are not sure whether the platform is stiff enough, reinforce it with one or more stiffeners to ensure that it does not flex under your weight and give a false ramp angle.

Studies performed in a science lab typically have protocols that ensure that apples are being compared to apples. Subjective drills done without such protocols or technical supervision may not be as accurate. But they will give you a kinaesthetic sense of how ramp angle affects your stance on skis and especially where the Tipping Point is where the amount of ramp angle has a negative effect.

Drills

Drills are best done barefoot on both feet (bipedal stance).

Drill 1

  • Assume an upright stance on a hard, level surface like a tile or wood floor. You should feel slightly more pressure under your heels than under the balls of your feet. Pay close attention to the sensations in your feet, legs, buttocks and back.
  • Move forward in the hips until you feel the pressure increase under the balls of your feet. Pay close attention to the sensations in your feet, legs, buttocks and back and note any changes.
  • Now do the same drill on the Stance Ramp with 2.5 ramp angle.
  • Note any changes in the pressures felt under the heel and balls of the feet and especially the sensations in your legs, buttocks and back.
  • Go back and forth between standing on the hard, level surface and the Stance Ramp and compare the pressures felt under the heel and balls of the feet and especially the sensations in your legs, buttocks and back.

Do you feel the same or stronger and more stable on the flat hard floor or on the Stance Ramp with 2.5 degrees of ramp angle?

Drill 2

  • Starting on the hard, level surface, relax your ankles and allow them to assume the Resistive Shank Angle. Bend forward slightly in the waist to find a comfortable, balanced position. Pay close attention to the sensations in your feet, legs, buttocks and back.
  • Move forward in the hips until you feel the pressure increase under the balls of your feet. Pay close attention to the sensations in your feet, legs, buttocks and back and note any changes.
  • Do the same drill on the Stance Ramp. Go back and forth between the hard, level surface and the Stance Ramp and compare the pressures felt under the heel and balls of the feet and especially the sensations in your legs, buttocks and back.

Do you feel the same or stronger and more stable on the flat hard floor or on the Stance Ramp with 2.5 degrees of ramp angle?

Drill 3

In checking the Net Ramp Angle of a sample of the boots and bindings of recreational skiers I have found that it is usually about 5.0 degrees. What I term the Critical Angle seems to be above 3.0 degrees. Studies need to be done to confirm this. You can quickly get a subjective sense of how 5.0 degrees of ramp angle affects your stance in skiing by doubling the 2.5 degree angle of the Stance Ramp

  • Place a shim of the same thickness  under the load point of the rear shim of the Stance Ramp as the shim that was used to achieve the 2.5 degree angle in the Stance Ramp. This will double the 2.5 degrees of the Stance Ramp to 5.o degrees.
  • Do the same drills as Drills 1 and 2.
  • On the 5.0 degree Stance Ramp, play close attention to the pressure under the heels and especially any changes in perceived stability as you move forward in the hips to increase the pressure under the balls of the feet.

Where do you feel strongest and especially most stable? With the pressure under your heels or under the balls of your feet?

Drill 4

  • Do the same drills as Drills 1 and 2 except alternate back and forth between the Stance Ramp with 2.5 degrees of ramp angle and the Stance Ramp with the 2.5 degree shims in place that increase the ramp angle to 5.0 degrees.

At which angle do you feel strongest and especially the most stable; 2.5 degrees or 5.0 degrees?

In my next post, I will discuss fine tuning ramp angle with the Stance Ramp

 

SKI RACING: AN UNLEVEL PLAYING FIELD

Ski racing is a lot like a lottery. With rare exceptions, equipment, but especially ski boots, can create what amounts to an unlevel playing field, one that can prevent racers from performing to their full potential. Because of the often significant physical differences in the feet and lower limbs from one competitor to another, the degree to which racers can be compromised by equipment varies greatly. This can be especially true if a racer happens to stumble upon the right combination. In ski racing, although luck is a factor, having the right feet with ski boots that allow them to function the way they were intended to can be everything.

Back in 1977 Lange was the only boot I had found of that allowed me to literally build a pair of race boots from the ground up. Like  Alan Trimble (boot tech for Lange USA), I was starting the process with a shell bottom and adjusting cuff side cant and forward lean angle of the rear spoiler to conform to the racer’s legs. In other words, I was building every pair of boots to each racer’s individual functional specification. But I was adjusting two other things that no one even seemed to even be aware were issues; net ramp angle and position of the ball of the foot and big toe in relation to the ski edge underfoot.

Net ramp angle is the inclination of the sole of the foot in relation to the surface of the snow. It affects the muscles a racer can use and especially the ability to apply force to the fore body of a ski and the ability to activate what I call the auto processes of edge control and turning forces. Two factors contribute to forward inclination; 1) the ramp angle of the boot board that the sole of the foot is supported on and , 2) the angle created by the heel and toe plates of the ski binding. I don’t know where they are today, but back in 1977 ramp angles were all over the map in both boot and binding brands and even models. Because of this, both the base angle of the boot sole plate and binding had to be considered as a unit in determining net ramp angle. Although few if any were aware of this issue, to me it explained why a racer’s skiing and results sometimes went downhill when they changed to a different ski binding or boot or worse, changed both. The generally accepted assumption, one that persists even today, is that a good athlete can ‘adjust’ to their equipment. Because of this, boots are not considered a factor. Fast skis are everything. While it is true that a talented racer can ski in just about any equipment, adaptation comes at a cost. The cost comes in the form of a reduced ability to perform.

If a NASCAR team were to announce that they intended to enter a stock sedan right off the showroom floor with no modifications in the Daytona 500 and that they would be competitive because their driver would ‘adapt’ to the lack of power and handling of the car they would be laughed off the circuit. If a world class sprinter announced that he or she that was going to compete wearing stiff leather dress shoes and that they would ‘adapt’ to the considerable limitations of the footwear no one would take them seriously. Yet most coaches, and even some racers, tend to minimize the role of the ski boot. When a racer dominates his or her competitors it is attributed to ‘exceptional talent’ and they are elevated to the status of a god with mystical powers.

In a November 13, 1990 Globe & Mail article appropriately titled, Boyd putting best foot forward,  Whistler’s Rob Boyd describes how the boots I had built for him changed his skiing and renewed his enthusiasm for racing. Said Boyd, “In Chile, I skied easily. It was fun again. It rekindled my love of skiing. Everything was so smooth…….” Boyd went on to say how he used to only worry about a solid fit in his boots, how he skied from the ankle up and that after skiing in the boots I had made for him he realized, “how much the foot can be used and should be used.”  Earlier that year my coaching counterpart, Glen (Meister) Wurtele (head coach of the men’s team), had summoned me to action in the World Cup Wars to work on Rob’s boots. After preparing his boots in my Whistler shop I flew to Portillo, Chile to hook up with the Canadian Ski Team who were training on the summer glacier.

The next day I was standing on a knoll about half way down a 45 second downhill course behind the lodge with the team coaches when Boyd took his first run in his new boots. When he came into view Boyd was skiing so differently that the coaches standing with the Meister and I didn’t recognize him. They were sure it was another racer. As he drew near, it became obvious that it really was Rob. When the coaches began to speculate as to what to what had caused such a dramatic change in Boyd’s technical skiing Wurtele said, “It’s his new boots”. The coaches were emphatic, ski boots could not possibly affect a racer’s skiing to that degree. Yes, they really can. In future posts I will explain why.