Individual Review CARV

[PisteOff]

Carv helped me become a better skier. The amount of progress made after several sessions was, for me and at that stage of my skiing, substantial and undeniable. The improvement was obvious to not only myself, but others I skied with. It’s been a few seasons since I’ve used it. It is my intent to purchase a new pair of 70-80mm skis (Stockli and/or Blossom) and revisit Carv. I’ve concentrated primarily on steeps, bumps, and chunder the past few seasons at the cost of my carving progression (and my knees).

I know overthinking every little detail of my skiing or every little detail/aspect of how well designed, engineered, and implemented the Carv system may or may not be is not an efficient use of my time and quite frankly just sucks all the joy out of it. It works, it’s fun. Put some earbuds in your helmet, grab some alone time on some rolling ripping groomers, and run some drills. The perfection of either its methodology, instrumentation, and/or instruction are pretty irrelevant to me. What it does do is put you in a good fore/aft space, it gets you on the outside ski with decently placed foot pressure. (It does a number of other things, just keeping it simple) Once there your own small motor skills, sense of balance, coordination, and sensory feedback begin to dial themselves in. It’s pretty obvious when you do it right. You’ll laugh your ass off when you first start to really hook up turns and get tossed on your ass.

It’s the cost of a fine dining outing with a couple drinks for two…….

 

[Mike King]

https://www.researchgate.net/publication/258035792_A_Comparison_of_Ground_Reaction_Forces_Determined_by_Portable_Force-Plate_and_Pressure-Insole_Systems_in_Alpine_Skiing

It is both my opinion and a fact confirmed by several research studies using pressure plates and other measurement devices. It is also consistent with the teaching systems of several ski instructor associations and race associations, including Austria, USSA, CSIA, APSI, PSIA, etc. One of first studies to find this result was the Birdcage experiment conducted by Dave McPhail in the early 90's that showed that WC skiers placed almost no force on the cuff of the boot longitudinally but substantial pressure on the cuff laterally. From the paper linked above:

From a biomechanical perspective, the reasons why skiers’ levels, certain turn phases, different skiing modes and pitches had significant effects on the differences are stated below. According to the studies by Müller and Schwameder (2003) and Schiefermüller et al. (2005), a skier’s center of gravity during skidded turns (low dynamic skiing mode) was found to be located nearly above or slightly forward (in anterior) to a skier’s ankle joint (average value during a turn). In contrast, a skier’s center of gravity in carved turns (high dynamic skiing mode) was located behind (posterior) the ankle joint. These findings are in agreement with the recommendation by the Austria Ski Teaching Concept (Wörndle et al., 2011). Additionally, the range of motion, as determined by the anterior/posterior movement of the center of gravity, is typically greater in skidded turns compared to carved turns. As a result, skiers may lean more on the boot shaft; hence, the support function of the ski boot may be greater in skidded turns compared to carved turns. Consequently, the force acting on the shank could be increased, resulting in an increased difference between the forces determined by the PI and the FP system.​

 

[RSTuthill]

On the edge angle question, the footbeds are installed and the boots are placed on a flat surface to calibrate what zero looks like. So if your boots are canted, that should be taken into account in calibration. Again though, whether it is measuring an edge angle at 42* or 45* isn't really the point of it. I think it's more useful to understand whether the movement you just incorporated into your skiing increased your edge angle relative to your usual score than it is to understand the absolute number.

I just want to know if the edge angles are actually measured or are they inferred from an AI algorithm or experimental correlation of other parameters. Seems like a pretty straightforward question and germane. And if actually measured, what type of instrumentation was used? The latter point is informed by my experience with canting which led me to conclude that small differences in angle make a big difference in performance. So accuracy is important. (I wasn't talking about the zeroing calibration.)

 

[Mike King]

I just want to know if the edge angles are actually measured or are they inferred from an AI algorithm or experimental correlation of other parameters. Seems like a pretty straightforward question and germane. And if actually measured, what type of instrumentation was used? The latter point is informed by my experience with canting which led me to conclude that small differences in angle make a big difference in performance. So accuracy is important. (I wasn't talking about the zeroing calibration.)

angles are measured using a 3 axis gyroscope.

 

[RSTuthill]

angles are measured using a 3 axis gyroscope.

Thanks, Mike. Can you tell us where the motion/attitude sensor is mounted? In the pressure insole or in the boot-attached battery pack? Guessing the latter.

Also, thanks for the academic paper link in your previous post. I will get into it today or tomorrow. As usual, when reading a paper with specialized nomenclature with which one is not familiar, you have to start looking up definitions. So I took a run at the Worndle et al paper for that and found it is in German. Do you know what is meant by "High dynamic skiing mode" and Low dynamic skiing mode"? I am guessing the terms refer to stance, since short radius (slalom) turns are normally performed in a higher stance than long radius (GS) turns. Other than that I am clueless.

Thanks again.

 

[Seldomski]

Does CARV also use sensors in the smartphone (ie GPS position and velocity) in its analysis? Or is all data provided solely by the CARV hardware/sensors?

 

[LiquidFeet]

Thanks, ....Do you know what is meant by "High dynamic skiing mode" and Low dynamic skiing mode"? I am guessing the terms refer to stance, since short radius (slalom) turns are normally performed in a higher stance than long radius (GS) turns. Other than that I am clueless.....

"Dynamic" usually refers to the degree you are bending the ski. More ski bend = more dynamic skiing. The skier needs to be doing multiple things to get a high amount of bend in their skis (assuming frontside skiing on modern cambered skis). I would think the intensity of the things the skier does to get the skis to bend (along with their rate, tempo, and duration) will determine whether the skiing "mode" is considered high or low dynamic.

I'm not familiar with technical talk here in the US referring to skiing "mode," but that may just be me. However, "dynamic skiing" and "dynamic turns" are both used frequently.

 

[RSTuthill]

"Dynamic" usually refers to the degree you are bending the ski. More ski bend = more dynamic skiing. The skier needs to be doing multiple things to get a high amount of bend in their skis (assuming frontside skiing on modern cambered skis). I would think the intensity of the things the skier does to get the skis to bend (along with their rate, tempo, and duration) will determine whether the skiing "mode" is considered high or low dynamic.

I'm not familiar with technical talk here in the US referring to skiing "mode," but that may just be me. However, "dynamic skiing" and "dynamic turns" are both used frequently.

You might be right, but if you read the paper, both groups of skiers are doing High and Low dynamic modes, the "Experts" who are carving, and the "Intermediates" who are deliberately skidding their turns.

 

[LiquidFeet]

Z-shaped skidded turns, linked hockey stops, and turns where the turn entry is rushed so the skis cannot get a grip on the hard snow are exhausting. And noisy. The skier is essentially bracing and braking against gravity all day.

Are the people who wrote that paper using "dynamic skiing mode" to refer to these exhausting ways of making turns? Do you think that they mean that the athletic demand on the skier determines whether the turn is dynamic or not?

 

[RSTuthill]

Z-shaped skidded turns, linked hockey stops, and turns where the turn entry is rushed so the skis cannot get a grip on the hard snow are exhausting. And noisy. The skier is essentially bracing and braking against gravity all day.

Are the people who wrote that paper using "dynamic skiing mode" to refer to these exhausting ways of making turns? Do you think that they mean that the athletic demand on the skier determines whether the turn is dynamic or not?

All the High dynamic modes are short radius turns and Low dynamic modes are long radius turns. These terms were not used to denote skidded or carved turns. Both expertise levels performed both modes.

 

[Mike King]

I don't know what the authors meant by high and low dynamic turns, but I would bet they mean high dynamic turns approach pure carved/race carved turns, and low dynamic turns are steered and/or skidded. Intermediates might attempt a pure or race carved turn, but are less likely to be successful in accomplishing it. I seriously doubt that the difference used by the authors was short versus long turns as that would not be the differentiator in the multiple ski instructor associations that I'm familiar with.

Also, LF, I don't think the differentiator is the bend in the ski per se, although a high dynamic turn will have more bend than a low dynamic turn according to the associations I'm familiar with. Note that a well executed hockey stop would have a fair amount of bend in it but wouldn't be considered a high dynamic turn...

 

[LiquidFeet]

I don't know what the authors meant by high and low dynamic turns, but I would bet they mean high dynamic turns approach pure carved/race carved turns, and low dynamic turns are steered and/or skidded. Intermediates might attempt a pure or race carved turn, but are less likely to be successful in accomplishing it. I seriously doubt that the difference used by the authors was short versus long turns as that would not be the differentiator in the multiple ski instructor associations that I'm familiar with.

Also, LF, I don't think the differentiator is the bend in the ski per se, although a high dynamic turn will have more bend than a low dynamic turn according to the associations I'm familiar with. Note that a well executed hockey stop would have a fair amount of bend in it but wouldn't be considered a high dynamic turn...

What I was trying to get at was amount of "ski performance" determines the amount of "dynamism" in the turn. Or in the skiing.

But then that frequently used but rarely explained term "ski performance" needs to be defined. I find that hard to do without a lot of words. I hope somebody will chime in with a clear and brief verbal description of "ski performance."

 

[Mike King]

Tom Gellie would define ski performance by the track left by the skis. High ski performance is two pencil lines left by the edges. Lower ski performance comes with some displacement evident in the track -- pretty high ski performance might only have an inch or two of skidding in the top of the turn, but the track through edge change would be purely carved. Low ski performance would be pretty major displacement that continues all the way into edge change and the edge change is skidded, not carved.

Another way to look at it is what is happening to the preservation of energy throughout the turn. Highly dynamic skiing redirects the mass with minimal loss of energy coming through friction, and the speed accumulated from turning the skis down the hill is preserved with minimal loss through the bottom of the turn. Low dynamic turns give that energy up to friction against the hill. Highly dynamic skiing controls speed through turn shape, but the turn shape is tightened or loosened by the skier based on intent. It is offensive skiing -- I want to go there. Low dynamic skiing is defensive skiing -- I want to slow down, and the result of the turn takes the skier to an outcome, not a choice.

Perhaps an image starts to help. Here's Paul Lorenz showing low dynamic to high dynamic turns:

 

[Lorenzzo]

Finally had my first experience in my CARV set up Lang RS 130s today. Very impressed. It had no trouble honing in on my known early season flaws. It’s simply fantastic to get scored after each run and receive reminders/tips after getting off the lift. I haven’t explored all of the features and data but my initial impression is it’s an effective gateway for improvement.

This evening when I opened the app on my iPad there was an array of videos and drills addressing suggested areas of improvement based on today’s skiing.

 

[Zirbl]

The fact of the matter is that there isn't, to my knowledge, a pressure plate or pressure sock instrument system that is available to the general public.

Pretty much what David Mcphail was trying to achieve with the Birdcage, with the addition of the ability to interfere with the pressure at different points to empirically establish the effect of fit. I recall he voiced disappointment with Carv similar to that expressed by @RSTuthill , in relation to the foot against the shell wall.

My own reservtion was that by using what they called something like top-end ski instructors, they were potentially confirming the coaching manual rather than reevaluating it by finding out what someone like Hirscher or Ligety is doing. Looks like they've answered that one.

Edit: I see you referred to the Birdcage later on.

 

[Zirbl]

High ski performance is two pencil lines left by the edges.

Aliprandini might disagree.

pretty high ski performance might only have an inch or two of skidding in the top of the turn, but the track through edge change would be purely carved.

And Mr. Gellie himself has plenty of videos I think you'd describe as showing high ski performance where he's doing exactly that.

@RSTuthill Wörndle et al. is just an Austrian coaching manual, haven't read it but every now and again Austria comes up with some arbitrary idea of how good skiing should be defined and how it should be foisted on tourists.

 

[Swiss Toni]

I wouldn’t dismiss that publication as “just an Austrian coaching manual” it’s the section of the official Austrian snow sports teaching manual https://hollinek.at/products/snowsport-austria-1 that covers alpine skiing. In Austria I think it’s mandatory for all ski schools and ski instructors to teach skiing in accordance with the official teaching manual, if you don’t you risk losing your license. Thousands of snow sports instructors depend on it for their livelihood.

Over the years the Austrians have exported their ideas about ski teaching to other countries, so their ideas are embedded in many other countries ski teaching systems. Unfortunately, Austrian ski school teaching along with ski school teaching in all the major alpine countries is very much aimed at tourists. The teaching manuals get revised from time to time, the Austrian’s last revised theirs in 2015 when they introduced “Schönskifahren” (elegant skiing)



The people behind CARV don’t seem to know much about skiing, so they will have likely had to rely on the input of ‘experts’ such as ski instructors. I suspect that behind the slick GUI, there is probably a lot of dodgy thinking.

 

[RSTuthill]

Wow, I step away for a couple days and all sorts of postings appear. I probably should not be commenting before doing all the due diligence I said I would do, but what the heck? At some point I am just gonna send Prof. Scheiber an email with a list of questions on the Nakazato et al paper, but off the top of my head these are some interim comments on the overall topic.

First of all, I am unsure what is meant by vGFR in Nakazato. Aerospace papers, in the ASME for instance, pay rigorous attention to nomenclature definition. I guess in bio-mechanics, not so much? I assume what is meant is the total force in the sagittal plane perpendicular to the ski base? Is that a good assumption? Otherwise I do not know why this paper would be germane.

Second of all, Figure 5 of the paper makes the point I was trying to make. Shin loading of the boot cuff is very important. Almost all of the differences between the pressure insole measurements and the force plate measurements are almost surely due to shin loading of the boot cuff. What the authors call shank forces. This caught me off guard when I first read it because the boot shank is in the sole of the boot in American usage. In this usage they are talking about the shank bone, or the shin, however.

Third, the authors allege that the center of gravity of very high level skiers is almost always above a point on the ski behind the ankle. To which I would reply "which ski and in what portion of the turn"? Remember there is the issue of sagittal ski split during the highest loading phase of the turn so to begin with this statement is not well defined. Secondly, if we are talking about the outside ski only, then I would submit that would be a priori evidence that the skier was in the back seat. And this sounds very much as if the conclusion was derived from pressure insole data. But what I found most curious is that the authors had taken force plate data that should have resolved the issue. There were two force plates on each ski, one under the toe and one under the heel. And yet they chose not to publish them.

Fourth, I would note that there are two ways of pressuring the cuff of the boot. With the balls of the feet unweighted via dorsiflexion of the foot and without such unweighting. It makes a big difference in the distribution of load on the ski. Thus the force plate method is required.

Fifth, in the interest of full disclosure I pretty much carve all the time. Laying trench as it is called, which may be an eastern expression, I dunno. Depending on the ski in use, I can also make the tips or tails of the skis skid out, usually at the bottom of the turn. But I am always eager to learn which is why I am posting here. I think that what bothers me is the idea of a system that tells you to ski in a certain prescribed manner. For instance, in Nakazato, the data show a typical stand on the outer ski technique. But if you want to be quicker to the next edge, you have to engage the inner half much earlier in the turn, perhaps starting to load the inside ski as soon as the fall line is crossed. In my opinion there are many ways to ski successfully, and I am somewhat skeptical of a system that would push the skier in one direction of another. I would like to see the data and make my own decisions unencumbered by skiing IQ scores and coaching recommendations. So I am going to continue to explore the CARV capabilities.

 

[Zirbl]

I wouldn’t dismiss that publication as “just an Austrian coaching manual” it’s the section of the official Austrian snow sports teaching manual https://hollinek.at/products/snowsport-austria-1 that covers alpine skiing. In Austria I think it’s mandatory for all ski schools and ski instructors to teach skiing in accordance with the official teaching manual, if you don’t you risk losing your license. Thousands of snow sports instructors depend on it for their livelihood.

I wasn't dismissing it, since I haven't read it, by "just" I meant it wasn't a research paper. But "Schön Skifahren" was exactly the sort of thing I meant by arbitrary idea.

I don't think you'd lose your license. I know someone who chucked their official stuff years ago, and I recall a friend who was qualifying saying there were differences between the east and the west of the country re. tip lead.

The people behind CARV don’t seem to know much about skiing, so they will have likely had to rely on the input of ‘experts’ such as ski instructors. I suspect that behind the slick GUI, there is probably a lot of dodgy thinking.

Instructors from Südtirol, if I recall correctly.

 

[Zirbl]

I guess in bio-mechanics, not so much?

Don't forget that along with the groundbreaking stuff, there are a lot of publications in sports science that are only superficially related to the second part of the term.

To which I would reply "which ski and in what portion of the turn"?

Equally surprised at how this is overlooked in the ski pressure studies I've read.

Third, the authors allege that the center of gravity of very high level skiers is almost always above a point on the ski behind the ankle. To which I would reply "which ski and in what portion of the turn"? Remember there is the issue of sagittal ski split during the highest loading phase of the turn so to begin with this statement is not well defined. Secondly, if we are talking about the outside ski only, then I would submit that would be a priori evidence that the skier was in the back seat.

Only if you've decided a priori that the centre of gravity needs to be forward of behind the ankle. Haven't you already described the alternative with dorsiflexion?