THE MECHANICS OF PLATFORM ANGLE: PART 5


In my initial posts on the mechanics of platform angle I demonstrated the physical impossibility of making a ski carve an edge into hard pistes at high platform angles with the snow by a skier aligning opposing applied and reaction forces with the vector perpendicular to the transverse plane of the platform of the outside ski. The reason for this is that the component of shear or slipping force will progressively increase as the angle of the applied force Fa becomes increasingly aligned with the plane of the surface of the snow as shown in the examples in the graphic below.

In my previous post I said that a reader who commented on Part 3 correctly stated for a ski to hold and carve at high platform angles required two separate forces acting on the transverse plane of the platform; one force oriented at 90 degrees to the plane and a second force oriented parallel or 180 degrees to the transverse plane with the vector acting into the surface of the snow. I ended my post by asking the reader what the source of the 180 degree force was.

The graphic below shows the answer. Elite skiers can make the outside ski of a turn hold and carve at very high platform angles because they are able to apply two separate forces in a coordinated manner. The reason I say ‘able to apply’ is that many factors can severely limit or even prevent the coordinated application of these two forces; the most significant factor being interference from the structures of the ski boot with the associated coordinated joint actions of the foot and leg.The graphic above is for the purpose of illustrating the source of the 180 degree force acting on the transverse plane of the platform. As such, the graphic  is not accurate because it shows the plantar (sole) plane of the foot oriented on the transverse plane of the platform. The actual mechanics and biomechanics are much more involved. I’ll start to explore the various factors in my next post.

4 comments

  1. Hi there. My countryman Aksel Lund Svindal uses size 42 ski-boots, but 44/45 regular shoes. He cuts a hole in the lining to be able to have the big toe extended. This video is in swedish/norwegian, but I think you still can understand a bit by the visuals..

    https://www.nrk.no/sport/slik-er-svindals-stovel-hemmelighet-1.7464490

    If you want me to translate anything, let me know. You can clearly see that the feet of arguably the best downhill-skier through many years are quite wide (from 08:10). You can also see how tight they fit his boots with foam etc. He says it is cold, but it is necessary to feel control at high speed.

    As a barefooter myself, having lots of trouble with my alpine boots – I am intrigued by your work. I think the best thing would be a boot with zero drop and room for toe-splay. But i still dont see how this is possible all the while we have to be solidly anchered to the boot or else feel unsafe and unstable at high speed and in difficult terrain.

    1. The video link doesn’t work. But I can see from the photo that Askel’s big toes are very straight as are his other toes with the exception of his small toe. Having the big toe aligned with the anatomic long axis of the foot is critical as is ensuring it can sit straight in the boot shell as I will explain in the next few posts.

      The perception of control is relative and dependendent on the means used to attempt to constrain the foot within a ski boot so as to achieve a secure connection with the ski. I explain the effects of attempting to achieve a secure connection by what I term indiscriminate envelopment in my post TIGHT FEET, LOOSE BOOTS – LOOSE FEET, TIGHT BOOTS. If the foot is contrained in a manner that inhibits the physiologic mechanisms that tension the structures of the foot rendering it into a dynamically rigid state postural responses will be inhibited and there will be no sense of security. The only option will be to increase the degree of constraint. Without the possibility of comparing the two methods of constraint in accordance with a strict scientific protocol even a racer of Askel’s calibre has no way of assessing the merits or validity of a tightly fit boot.

      The amount of drop or total ramp angle (zeppa + delta) is largely dependent on the length of the Achilles tendon. Room for toe splay – metatarsal spread is critical. Security results from the attenuation of arch decompression oscillation. I will discuss this in a future post.

      1. I am sorry – the video is obviously restricted to Norwegian viewers. My point was that one of the worlds best alpine skiers for many years is winning despite having a very uncomfortable and tight fit in his boots.

        I have read the post you refer to. I agree in the importance of the big toe being aligned, this is what I am working on in my boots. But if I size up to reach this goal, the overall looseness renders the boot useless in everything but perfect groomers or soft snow. At least – this is what I imagine and have felt earlier when having a boot that was to loose.

        I have been experimenting with removing the footbed and changing ramp-angle. I noticed a positive change when lowering the ramp angle. I guess finding optimal angle will take some work, but I feel it is equally or more important to get the necessary amount of space for my toes first. Also I have been experimenting with the tongue, and I really feel you have a point regarding the pressure from the lower part of the tongue.

        I must admit that a lot of the tings you are discussing are to complicated or technical for me to really grasp. I have read most of your posts though, and I`m trying to connect the dots. I am crossing my fingers for a future “summary post”.

        I take the liberty to ask you some questions here – and I fully understand if you do not have the time to answer it.

        Would you agree that the goal here is to be able to put on the ski boot and balance on one leg as easy as one does barefoot? Or is this a misunderstanding in your view? Have you found a boot that you could recommend checking out for “people like us”? I have one foot that is 26,5 and one that is 27,1. Currently ski in 26,5 boots. Would you size up if you had my feet? When you ski, do you tighten the clamps on the shaft tight enough for the liner to follow your movement, or do you have “open space” in which your shaft is moving? What about the clamps on the foot itself? loose? If you would be so kind to explain your set-up in short here, I would be very thankful.

        Again, thanks for all your work!!! This resource is extremely important in a world where most shoe- and bootmakers are going in the wrong direction.

        Erik.

      2. My point was that one of the worlds best alpine skiers for many years is winning despite having a very uncomfortable and tight fit in his boots

        I understood that. My position is that some skiers do well in spite of their equipment. One of the first things I discovered when I started working with elite skiers and World Cup racers is that they have much tighter foot structures than the average person. Because of this their feet require minimal 3 dimensional space in which to function. Steve Podborski had small size 6 US men’s feet that were very tight. He could put on a pair of ski boots right out of the box and ski better than most.In fgact he won an Olympic Bronze medal in boots that were far from ideal. But he easily won the WC Downhill title in boots using a new system I invented based on principles of engineering. Elite skaters and hockey players also have very tight feet. They can rise to the top of their ranks despite the limitations of their skates which are custom lasted. But may not represent their full potential. Please see my posts on Bio-Engineering in which my first efforts at skate modification produced improvements in quantifiable metrics on a scale never seen before.

        I have read the post you refer to. I agree in the importance of the big toe being aligned, this is what I am working on in my boots. But if I size up to reach this goal, the overall looseness renders the boot useless in everything but perfect groomers or soft snow. At least – this is what I imagine and have felt earlier when having a boot that was too loose

        The problem is that the structures of your foot are not maintaining intrinsic tension. I’ll explain in future posts.I solved this problem in 1980. My solution took the stress off of Podborski’s knee and he was easily able to ski with an unhealed ACL and win WC downhill races.

        I have been experimenting with removing the footbed and changing ramp-angle. I noticed a positive change when lowering the ramp angle. I guess finding optimal angle will take some work, but I feel it is equally or more important to get the necessary amount of space for my toes first.

        The sequence is stance training/ramp angle optimization then room for the big toe.

        Would you agree that the goal here is to be able to put on the ski boot and balance on one leg as easy as one does barefoot?

        Yes. But you have to be able to create a platform under your outside. There is no way I know of to stand on air or even stand and balance on the inside edge of your foot. To balance on one leg on a ski edge there needs to be the equivalent ground under the ski. For some reason everyone has been ignoring this for decades. My position is that if one can’t explain how balance on the outside ski works they don’t know anything about skiing. Balance isn’t just important. It is everything.

        Would you size up if you had my feet? When you ski, do you tighten the clamps on the shaft tight enough for the liner to follow your movement, or do you have “open space” in which your shaft is moving? What about the clamps on the foot itself? loose? If you would be so kind to explain your set-up in short here.

        When I ski I have no sensation of anything on my feet. This includes no sensation of looseness. The only thing I am aware of is the feeling in the soles of my feet from the snow. Over the next few months I will explain in a step by step process how this is done.

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