DETERMINING OPTIMAL BOOT SHAFT/BOOT BOARD RAMP ANGLE


A follower of skimoves posed the following;

“I’m trying to determine my optimal boot shaft angle and ramp angle given my physiology – i.e. what works best for me. I’ve done some of this work on my own by adjusting binding ramp angle (last season). What is interesting is the shaft angle of my newer Head vs. Lange boots”.


As discussed in recent posts, the importance of the cumulative effect of boot board ramp (zeppa) and binding ramp (delta) angles on stance is becoming increasingly recognized. Although binding ramp angle (delta) typically varies widely from one binding to another in recreational bindings, boot board ramp angle seems to be coming into line with functional reality in race boots. Reliable sources in Europe tell me that the boot boot board ramp angle in World Cup boots is in the order of 2.6 degrees. After I eliminated the arch profile in boot boards for a 23.5 Head race boot, I calculated the ramp angle at 2.35 degrees, a far cry from the 5 degrees claimed for the boot boards. I calculated the boot board ramp angle of an Atomic race boot of a local ski pro at a little over 2 degrees. I have also been told that shim kits are available for all race bindings that allow the delta angle to be zeroed.

The default barefoot ramp angle for humans is zero. It has been unequivocally established that anything more than a small amount of ‘drop’ (heel higher than forefoot) in footwear will have a detrimental effect on stance, balance and movement patterns. This especially true for balance on one foot, something that is fundamental to sound ski technique.

Elevating the heel relative to the forefoot will cause the muscles in the back of the lower leg to contract. Over time, these muscles will become chronically shortened. The key muscles affected are the calf muscles; the gastrocnemius and soleus. But the small muscles that stabilize the knee and pelvis are also adversely affected, not a good thing.

If I want to find the optimal boot shaft angle and compare the shaft angle of two or more boots, I start by making the boot boards perfectly flat with the transverse aspect horizontal with the base of the ski. I set the boot board ramp angles for both boots at 2.5 or 2.6 degrees. Since it can take a long time for the body to adapt to even small changes in ramp angle underfoot, the angle is not hypercritical.   I have settled on 2.5 to 2.6 degrees of total ramp (zeppa + delta) as an arbitrary starting point. Although there appears to be a positive effect of a small delta binding angle in SL and GS, I prefer to work with a zero delta angle initially since a positive or negative delta affects the shaft angle of a ski boot.

When moving from one boot model to a different model or to another boot brand, the first thing I do is remove the boot boards and calculate the ramp angles with the top surface monplanar. If the boot boards are not flat, I plane or grind them flat. If a new boot is to be be compared to a current boot with a boot board angle of 2.5 to 2.6 degrees, I modify the boot board of the new boot so it has the same angle as the current boot.

Next, I compare the shells and the angles of the spine at the back of the shaft of each boot. Even if the angles of the spines of the boot shells appear similar, there is no guarantee that what I call the static preload shank angle (more on this in a future post) will be the same.

A quick check of how the structure of the shell of the new boot is affecting the functional configuration of the foot and leg compared to the current boot, is to put the current boot on one foot then put the new boot shell with the liner from the current boot on the other foot. If a significant difference is perceived, the source is the new shell.

At this point, it may be apparent that there is a difference in the shank angles of the left and right legs when comparing the current boot to the new boot. But whether one boot is better than the other or even if one boot eanables the optimal static preload shank angle would not be known. I will explain how I identify this angle in my next post. For now, study this recent video of Lindsey Vonn starting off by skiing in what appears to be a strange ski stance. In fact, the exercise Vonn is doing is a familiar routine to me, one that I do before I start skiing – https://www.facebook.com/LindseyVonnUSA/videos/10154672700589728/

Why is Vonn skiing this way? What is she trying to do?

Also, check out this screen shot of Anna Fenninger. Note her compact, forward in the hips stance.

fenninger-1

Finally, watch this video in which Brandon Dyksterhouse compares Shiffrin and Fenninger – Shiffrin GS Analysis – https://youtu.be/phchHWwDhdY

What do Vonn and Fenninger have in common? Why?

 

3 comments

  1. 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!!

  2. While I appreciate your efforts toward universal boot truisms, how do you factor in significant anatomic variations that exist. Example: if a skier has very limited dorsiflexion, would shaft angles and ramp angles vary significantly from your suggested ideal? And thanks for your blog. Quite engaging. Tom A

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    1. The reason I started this blog a few years ago was to attempt to answer issues such as you raise. In the paradigm of critical thinking, issues continue to evolve and become clearer over time. Even though I had identified ramp angle as a critical factor affecting skier performance as far back as the late ’70s I still had many issues that I wanted to explore and resolve. In the past two years, I have worked very closely with a small number of skiers and racers who either had longstanding problems skiing or suddenly began to experience problems. A sobering moment was when Mikaela Shiffrin’s skiing literally went downhill at the beginning of the 2014-15 World Cup season after she changed boots (or some aspect of her boots) in the fall of 2014. I called it almost immediately. That something like this could happen to a skier of her calibre confirmed my belief that research with a structured, systematic science-based program to assess and guide equipment setup,especially ski boots is needed. The ski industry should be funding this research.

      It is an irrefutable fact that elevating the heel relative to the forefoot more than a small amount will cause a shortening of the Achilles-soleus/gastroc and that this will have a negative effect on balance, muscle power and skier stance. Until about 2 years ago, I had arrived at an accumulative ramp angle of about 3 degrees by experience. Then I started to get comments from followers in Europe with ties to racing that the magic number was closer to 2.6 degrees. When I reduced the ramp angle in my boots (binding delta is zero) to 2.5 degrees, I was amazed by how much easier skiing instantly became. So given what is known, it is reasonable to start with a ramp angle of 2.5 degrees and then slowly fine tune it.

      Shaft angle is another whole matter. If a skier has significant pathologies that limit dorsiflexion, their skiing ability will be limited and compromise is the only option. A shortened achilles, which is common because of drop in shoes, is an issue. In order to arrive at optimal shaft angle, we need to know optimal for what end result? The current paradigm in the ski industry is shaped by what is called the information bias. The boot is considered as a handle attached to the ski with which to rigidly fix the leg of a skier to the ski so that even the slight movement of the leg is transferred to the ski. The end object is to render the foot and leg of the user dysfunctional. This paradigm continues be parroted even in recent patents.

      I am coming from the opposite direction. My end objective is a high level of function where skiing becomes what amounts to a reflex activitity because the processes of balance are potentiated. In my next few posts I will talk about the need to train skiers in the elements of stance and especially how to set up a static preload across the arch-Achilles juncture that enables the stretch reflex to engage. The angle of the shank in the static preload state is used to configure shaft angle and the amount of shank movement within the shaft. This process allows shaft angle to be tuned to the skier. Stay tuned.

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