or Connect
EpicSki › The Barking Bear Forums › Ski Training and Pro Forums › Ski Instruction & Coaching › A Discussion of David M's Hypotheses
New Posts  All Forums:Forum Nav:

A Discussion of David M's Hypotheses - Page 3

post #61 of 76
Arcmeister, I pretty much think the same thing only I have a slightly different definition of passive and active that I tend to use. Its late and my brain is shot. The last couple posts I have made have not felt entirely right to me but my brain is not telling me why. I need to go get some sleep I was on skis for 12 hours today. Yah see how babbling even this post is. I will probably read them again when I am not tired.

[ January 16, 2003, 08:50 PM: Message edited by: Pierre ]
post #62 of 76
for wear the fox hat, atomic made a dual radius ski th e 9.28 back about 1995. i believe that it was their 1st beta lobed ski.
maybe david can explain why symmetrical skis can make parallel
tracks, or is it as simple as the unweighted ski is under less force therefore needs less force to turn?
spent the day at local 200ft hill working to balance boots(fine tuning) basic fit and foot beds by jesse at sign of the skier in toronto (recomend for boot fitters list). basically was trying to match pressure at big toe,little toe and heel while keeping edge engagement solid but not till ski out from under body. proved warrren withrell's 80/20 rule again and maybe some points for david's balance theories too. the last 2 strips-
big difference,legs relaxed, arcs cleaner, no fighting the turn, could litterally walk down the hill,walking lunges probably more accurate(lisa-good ski exercise?). i was trying to experiment with david's comments about the lead foot going to the outside edge and the trail foot going to the inside edge. all i did was slide the new inside foot forward at transition, the skis almost edged on their own, added knee angulation just changed how tight the turn radius was. skiing suddenly was very easy and simple( after 10 years). did notice that getting the new inside foot even or ahead made big difference in staying clean in turn and staying out of the backseat.

david ? is extending the outside leg in the top half of the turn to keep pressure on the ball of the foot what prevet the ski from railing out of a turn?
jim

[ January 16, 2003, 10:02 PM: Message edited by: jw252 ]
post #63 of 76
Quote:
Originally posted by jw252:
all i did was slide the new inside foot forward at transition, the skis almost edged on their own, added knee angulation just changed how tight the turn radius was. skiing suddenly was very easy and simple( after 10 years). did notice that getting the new inside foot even or ahead made big difference in staying clean in turn and staying out of the backseat.

jim
This is old school technique, and it works well enough on straight skis. (My daughter taught me this 8 years ago and she got it from a PSIA examiner.) Sliding the inside foot forward, together with extending your outside leg, puts most of your weight forward on the outside ski. This makes intitiating the turn easier. The problem comes in when you need to move your weight to the inside ski (either because a "snow snake" gets your outside ski or because you are in soft snow or because you want to start a new turn in the opposite direction). At that point pressuring the inside will put you in the back seat. With shape skis, we simply don't need very much forward pressure to engage the tip of the ski in the new turn, so we can initiate a turn without shuffling to force our weight forward. That's the reason coaches are emphasizing less counter and minimal lead change.
Minimal lead change and good balance over both skis is the essence of modern two-footed skiing. That is what allows us to manage pressure between both skis as conditions require: more equal weighting in soft snow, almost completely to the outside on hard so, and anything in between, or even 100% on the inside when we lose the outside edge.
As Pierre has pointed out, David M may (or may not) accurately describe the reflexive balancing aspects of walking, but the discussion of ski technique is generally stuck in obsolete technique.

John

[ January 17, 2003, 08:39 AM: Message edited by: John Dowling ]
post #64 of 76
You know guys, not that it matters if you care what I think or not, but I'm not going to read this part of the forum anymore. Not that you care about that either. I feel sorry for anyone who has to think about extending this leg or pressuring this part of the foot or leading with this edge or what ever the case while skiing down the frickin hill. I know you guys have your engineering degrees and all but do you actually ski with thoughts in your head about what force initiates the turn while turning or what force one should make to correct the edge you just caught on the groomer rut in the snow. What do you think goes through everybodies head while they are skiing? Any of this? If I had to think about all this motion crap while skiing just to turn properly I'd take up snowboarding.

Sorry, I snapped, I think!
post #65 of 76
Lars, your wisdom is obvious.

Your point is exactly what I said about balance in the "Balance" thread from which this one comes.

The pseudoscience tossed about so casually and so self-importantly stands directly in the way of enjoyable skiing. At the risk of being offensive (nothing new for me!) I find the hypertechnical pseudoscience in skiing usually comes from engineers or engineer-wannabes. Something about the engineering vocation and training creates a need to make simple things technically complex.

I guess it's something like how law school turns normal people into professional paranoids.

Anyway, the main issue with David's research is his starting point. It appears that he has a rather large misunderstanding or knowledge deficit w/r/t biology and anatomy. If that's true, I don't know how his "experiments" or "theories" can be substantiated, much less replicated.

I'd prefer to address balance issues with balance exercises, and not through an overlay of engineering analysis.
post #66 of 76
Yes, David, that's what I was saying. You got Pierre all mixed up about where you want the extension. I had to read what you said a few times myself before the light went on.
Anyhow, I think David is presenting us with something very useful, and if your equipment allows for it ( I think my boots could be a little wider at the big toe), you really should give it a try. It really does FEEL like walking, even though there is no actual step.
post #67 of 76
And as always Gonz, "You Da Man" Wish I could ski with you!
post #68 of 76
Oooooh I can just pictur Lars dragging his knuckles on the snow. Especially dragging a sled through the bumps. [img]graemlins/evilgrin.gif[/img]
post #69 of 76
Not a pretty site huh Pierre? You know the old addage, "You can't teach an old dog new tricks" in this case it's probably true. Besides, after having reconstruction of both shoulders, you'd never see me on a snowboard. I've hauled too many boarders off with shoulder injuries to even think of it.

I will stick to what I said before though. Do you teckies really think like that while skiing? For Gods sake! No wonder some of these people are having trouble learning how to ski. They are thinking too much instead of just doing it. I guess that's one of the reasons I wouldn't want to be an instructor, and probably why I've never paid for a lesson. :
post #70 of 76
Oh come on Lars, you've skied with me, how much thinkin did I do in relation to how much fun we had. That's funny comming from a guy who was one of the original techies on this site. You at one point held the lead in the number of posts. Way above anyone else. [img]tongue.gif[/img] [img]tongue.gif[/img] [img]tongue.gif[/img]
Gots to get over the HV and prove to you that I disengage brain while skiing. Maybe towards the end of the season. [img]graemlins/thumbsup.gif[/img]

[ January 17, 2003, 06:33 PM: Message edited by: Pierre ]
post #71 of 76
Yesterday I had a couple of buddies from texas in an all day private. One had never skied before, one had skied twice. Last run of the day was on a green run from the top of the mountain. Pretty awesome for the first timer. Anyway, in trying to give a good picture for the second timer who was skiing very open parallel, I had him following me. So I simply applied DM's simple movement pattern. I 've been playing with this alot lately. Anyway, the statement this guy made when he skied up to me was, "You looked like you weren't even moving. It looked so easy." That in a nutshell is what it is. So damn easy. Go out and try it. I can't find an easier way to move my Cog from one ski to another than this. Even if move into the dynamic relm and start laying tracks on blue groomers it works. And don't go off on this one footed two footed thing either. It's neither. It's the structure working as it was created to work. Nothing more, nothing less. There's no artificial tip lead, or artificial squarness, or stepping up the hill. It leads to natural effective stance that's adaptable to everything from wedge turns to dynamic parallel.

If you are a student of skiing and are interested in learning, open your mind and go try it. What's to lose? I don't think DM created anything, he just simply identified something that has been ignored by the main stream. And it's right in line with something presented to me by an examiner last year. Movements initiated by the feet, powered by the legs, and controled by the hips. That's ceturies old martial arts wisdom, and it's as natural in skiing as it is in tai-chi. :
post #72 of 76
MilesB and RicB thanks for your support.

For everyone's information I have never represented that I invented anything new. In fact I learned what I know today from watching great skiers such as Erika Hess, Vrenie Schnieder, Pirminn Zubriggen and the Austrians who seem to know exactly what I am talking about. And I don't think they just fell out of bed one morning and 'got it'. A few could actually stumble on to the technique I describe by chance. But it would be akin to winning a lottery.

If there is a problem it is that for whatever reason the great skiers I learned from can not or will not communicate what they do to others.

In life one can acquire wisdom by learning from those who are wise and who are great at what they do. This is what RicB, MilesB, nolo and I are trying to do. Once we 'get it'we can share the wisdom of the great skiers with the masses. Is anyone on epicski going to say that this is a bad thing?
post #73 of 76
jw25: david ? is extending the outside leg in the top half of the turn to keep pressure on the ball of the foot what prevet the ski from railing out of a turn?

DM: Just a quick comment as I am heading up the hill. It is too gorgeous a day to miss.

At initiation you have to shift the centre of pressure to the ball of the new stance foot. This will cause the foot to tip the ski onto its inside edge. The trick is that you have to keep pressure under the ball of the foot until you can bring the ski out of the fall line where you can use the forces acting on CM to drive the mechanism. If you don't keep pressure on the ball with active extension pressure will drift away from the ball as the ski comes around and it will rail out as you suggest because the edging force have been over powered by the external forces acting on CM. If this is not clear please ask questions.

Another reason to keep pressure on the new stance leg with inititial extension is to power up and maintain proprioception which is nerve input that gives your brain info about balance. Here the stance leg acts as a sensing mechanism to help the balance system position CM as the ski comes out of the fall line.

I will try and get to your other issues tomorrow.

Gone skiing!
post #74 of 76
Gonzo Strike; Anyway, the main issue with David's research is his starting point. It appears that he has a rather large misunderstanding or knowledge deficit w/r/t biology and anatomy. If that's true, I don't know how his "experiments" or "theories" can be substantiated, much less replicated.

DM: Gonzo guys you yourself and John Dowling crack me up. You sit back like high priests passing judgment on the rest of the world ruling on what is dated, what is modern and what is and what isn’t science. This is your opinion and you are entitled to it. The fact that you are unable to know how my experiments or theories can be substantiated may reflects a cognitive deficit you have. That you are unable to know something does not preclude someone else knowing.

My theory was that skiers produce a pressure signature like a fingerprint with the forces applied by their foot and leg. This signature represents the biomechanical output generated in a turn, in particular at turn initiation.

To validate the theory we assembled a team comprised of 2 Olympic medallists (one a multiple medallist) who were both World Cup champions for the ski component. For the science component we engaged a biomedical engineer who also taught courses at the University of Toronto among other things and a PhD in Anatomy who specialized in the function of the lower limb and the quantification of the moments of force acting across the joints.

Working with the science component I presented a model that predicted the sequence of biomechanical events associated with the utilization of (ground) reaction force for balance and the rotary or steering component. To test the model we designed a device that replaced the ski boot (on both feet) The device was instrumented with 18 pressure sensors positioned at specific anatomic sites to record forces on X, Y, Z axes. Input from each sensor was recorded on its own channel. The input was synched to video. The data obtained was clean and consistent on all channels and for all subjects.

As much as possible test conditions were standardized with one variable altered for each series of tests. The subjects were presented with challenges to see how their balance system would respond. This follows the protocol used in typical balance studies of which our science personnel were intimately familiar. The result of this research validated my model and my predictions of the sequence of forces applied by the foot and leg. If this doesn’t relate to skiing and/or it isn’t science then maybe you and Si are talking about something entirely different.
post #75 of 76
jw252: maybe david can explain why symmetrical skis can make parallel tracks, or is it as simple as the unweighted ski is under less force therefore needs force to turn?
DM: A bit more complicated than this. The mechanics of the outside and inside feet as they relate to the ski are completely different. Before I get into detail can you please explain your statement:
"basically was trying to match pressure at big toe,little toe and heel while keeping edge engagement solid but not till ski out from under body."

What do you mean by "match pressure"? are you saying the pressure should be equal or ?
post #76 of 76
Wear the Fox Hat, I apologize for the delay in responding to your thoughtful and insightful post which I thank you for. I had a busy weekend and with no time to absorb what you said.

FoX: David, Your comments yesterday got me thinking. Your issue isn’t with going straight, but with being on edge, according to what you said.
DM: To a degree. My issue is the ability to develop the most stable platform available under foot.

Fox: Now, when skiing, the edges are used to turn,
DM: More than the edges I believe we also need to apply twisting force about the long axis of the ski. But edges are definitely an issue in turning. I agree with your an analogy to the round about and your statement:
”For an object with width > 0, turning must consist of one or more of the above.”

and

”Likewise today, if we consider running, an athlete does not turn using 1. or 2., but only 3. To use 1. would require him stopping running to make the turn. To use 2. would twist his ankle. The only option is 3. to allow one leg to travel further than the other.”

Fox: At higher speeds, how does the runner achieve this sort of turning? Again, as far as I can see, there are three ways:
1. Change his stride pattern so the outside leg takes bigger strides, and the inside one takes smaller. Perhaps this is done at slow speeds or on tight turns, but it breaks the rhythm, and would unbalance the runner at speed
2. Put more weight on his outside foot. Now, due to centrifugal forces, this is more natural. At speed, his body will want to go straight on while he tries to turn, so there will be a greater force from his body acting through his outer foot. When this happens, it is almost as if 1. is occurring. The reduced force on the inside gives reduced grip and reduced power from that leg, so less distance is covered. This is one of the principles at work when a car turns a corner – you feel the car leaning out, and inside the car, you get pushed to the outside of the turn.
3. In a sense, the third way is “cheating”, because, instead of changing the runner, you change the bend. Put a bank on it. (and I don’t mean one with an ATM!). This allows the runner to continue around the bend without having to worry about changing weight or stride. And for this, I’ll give another car example: which is easier? Formula 1 or Indy Car? I would argue that Indy Car is easier, due to the banked circuits. The drivers can keep the speed up around a bend, while in F1, they have to back off the power to get around a flat, or slightly banked bend. If the driver doesn’t have to slow down, then there are less additional forces acting on him and the car while turning. And less forces = less stress on the frame.
DM: I think I see where you are going (please correct me if I am wrong). My approach is to develop a (relatively) stable platform under the outside foot (ski) to stand on so that when one turns the platform acts like the banked corner you refer to. But if used in the manner I propose the skier only inclines as required to balance the opposing forces. This recognizes that the optimal ‘bank’ angle is related to the speed of the skier (car) and the radius of the turn. Given the right mechanics the skier can control this aspect.

Fox: In skiing, until about 10 years ago, the technique involved a mixture of 2 and 3. There was a shift of weight and leaning onto an edge, which basically created the effect of a slightly banked turn. Then along came skis with increased side-cuts. The effect of the side cut was to give the ski more of a natural ability to turn, even before putting any pressure on it to flex it. This means the ski effectively adds to the banking of the turn. Before modern skis with their side-cuts came along, skiing was more akin to F1, requiring weight transfer as a major part of the turn, yet now it is more like Indy Car, maintaining speed through the turn by using the skis ability to carve.
DM: The pivotal issue here is the process that controls the angle of the ski in the snow. Prior to the new sidecuts skis had waist widths of 70 mm with shallow sidecuts. There were two problems in terms of platform especially on hard pack snow, 1) the ball of the foot was not far enough into the sidecut on the inside turn aspect of the waist and, 2) the sidecut was too shallow. This required too much force to get the ski on edge. And went it went on edge the sidecut was too thin to provide stability. In other words 2 critical mechanical considerations were wrong in terms of platform mechanics.
Reducing waist width while increasing sidecut closed the gap. Elevating the foot multiplies the force that can be applied with the ball of the foot into the sidecut area. Things are different on softer snow. Here a wider waist and deeper side cut are desirable to resist the penetration of the ski into the snow as it rotates onto its edge. A general rule is that a ski with a deep sidecut will assume a flatter angle on a flat surface than a ski with shallower sidecut even with the same counterflexion. Sidecut is a mechanism for progressively applying force to the snow that results in the generation of turning force.

Fox: So, as I see it, the easiest way to make a turn is to allow one side to travel further than the other, and to do this on a banked turn. Or, to put it another way, let the skis carve their way around the turn while not putting a large proportion of the weight/pressure onto one ski or the other.
DM: This is where my thinking diverges from yours. Either Fastman or Arcmeister referred to ‘the contribution of each ski to the turn'. Clearly each ski does contribute. So I prefer this term. But it is my position that the relative stability of the platform under each foot is weighted in favor of the outside foot.
In walking the balance system positions the foot under the trajectory of CM to effect balance for the new stance foot. In skiing steering has a similar effect. But as the forces increase in the 3rd phase of the turn it is my theory that CM must adjust more to the position of the stance foot than vice-versa. To do this requires that the skier be supported on a (relatively) stable platform. If it were not so then it would be exceedingly difficult for the balance system to position CM with any degree of accuracy.

Rather than pursue this train of thought how about if I start a new thread on the mechanics of the inside and outside limbs in a turn?

Thanks for your post. [img]graemlins/thumbsup.gif[/img]
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Ski Instruction & Coaching
EpicSki › The Barking Bear Forums › Ski Training and Pro Forums › Ski Instruction & Coaching › A Discussion of David M's Hypotheses