3-D motion capture comparison of elite WC SL skiers

Re: 3-D motion capture comparison of elite WC SL skiers

Postby Max_501 » Wed Dec 25, 2013 6:15 pm

theorist wrote:[As an aside, I think there's nothing wrong with someone coming on here and saying they disagree with you and wanting to challenge you (if they do it politely) -- after all, you yourself have no problems challenging others ("No one is bashing, what is happening here is healthy dissection of different approaches.") -- and just as it's perfectly OK for you to do this, it's perfectly OK for others to do it as well (we all have to play by the same rules).


No, this is not OK. We've been down this path before and it is a huge waste of Harald's time and we get very little of that as it is.

jclayton wrote:All sounds a bit strange , a bit like a scientific , postulating Leopold Bloom.


Indeed. At this point I'm getting more and more confused!

theorist wrote:I studied ACBAES1 extensively a long time ago -- 1998 -- so, granted, my memory may have gaps...


theorist wrote:I'm a serious, sincere student asking sincere, serious questions.


theorist wrote:I do have some experience with PMTS, but I won't claim a level of expertise I don't have, so I never said I was a serious student of PMTS. What I am is a serious student of skiing.
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby arothafel » Thu Dec 26, 2013 7:33 am

There is a pattern to this kind of thread. And it never ends well....

Just for the record, when I was first introduced to PMTS in 2005, I was also skeptical. After all, at that time EVERYONE who was ANYONE was teaching all of us Masters racers to widen our stance... get squared around the turn.... etc. So, who did this Harb guy think he was advocating a narrow stance and using a bunch of terminology that was not consistent with my "god-like" coaches.

Luckily for me, my profession puts me touch with some of the top sports coaches and researchers in kinesiology, sports bio-mechanics, etc. from around to world. As a personal favor, I asked a few to review PMTS (I sent books and videos) and tell me what they thought. After about a year (takes a long time when it's a favor) I started to get very positive feedback.

What was most interesting were the side notes and comments I received. Most of them being caveats that skiing is "unlike almost all other sports." And that, "there is no viable data to reinforce ...." I came to the conclusion, that even the experts don't really understand all the bio-mechanics of skiing. But, of everyone who was seriously looking at it, PMTS and Harald, in particular, had the best direction.''

So, the point is that if science is what you want to prove PMTS is valid, then simply read the materials. Go to a camp. Take a private. And, understand that PMTS is still a "work in progress." To this day, HH and coaches continue to work on their own skiing and recognize there is still more to learn and comprehend. Most recently the more efficient use of hands and poles (No Swing Pole Plant).

In addition, Harald does not say, "Trust me... you'll ski better if you do this or that." The books explain all the rationale behind the movements, drills, etc. It's NOT a blind-faith proposition.

At least for me... this is why these type of threads are so frustrating. The answers are available. Max, Harald, and others often spend time just "directing traffic" to point out to new forum members where the information can be found... Book, Chapter, Paragraph and Sentence!

But, at a certain point... enough is enough... and it does not end well. :wink:
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby jclayton » Thu Dec 26, 2013 7:57 am

One thing that stands out ,the more I think about , it is Diana saying that he is too advanced to go back to basics . That sounds much out of character . The basics are the nuts and bolts , even the best have to tighten them up from time to time .
F1 Ferrari mechanics do it all the time , especially to the heads !!!
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby h.harb » Sat Dec 28, 2013 12:30 pm

Thanks guys, some brilliant posts, great observations.
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby jclayton » Sat Dec 28, 2013 12:59 pm

Actually , the tone of the posts are very much like those of a certain disenchanted ex-member . Looks like another foray .
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby Kiwi » Sun Dec 29, 2013 12:51 am

I wrote a long post then managed to delete it. To paraphrase my thoughts:

Describing skiing outcomes, as suggested, in terms of mechanics may be interesting to some but for indentifying good skiing it is and will remain a waste of time.

Measuring outcomes in this manner will descibe precisely how a movement is being performed but it will not tell you what movements to make or when to make. Mechanical study of outcomes cannot resolve the arguments between different schools of skiing. More on this later.

Identifying good skiing is about empirical evidence and experience. Harald's blog and the comparisons to ski races are used by him to explain and educate us about Pmts, his theory of skiing he derived from the empirical evidence found on the slopes and race coursse, based on his experience and knowledge of biomechanics. I see the study of 3D as useful in this educational sense.

It is not possible to backwardly engineer a theory of skiing from measurements of outcomes. Who decides what is in fact a good movement outcome and therefore to identify the ideal movement? Such calls must be based on experience. It is not as simple as saying Hirshers movements are always better because he is generally faster in salom.

The perfect turn is an ideal for most of use most of the time. Indeed, racing just makes the perfect turn harder. However this does not invalid studying racers, the contrary, racers aim for perfection in difficult circumstances so the movements of racers are closer to the raw or base essentials.

I know PMTS IS the superior way to ski based on the empirical evidence, ie I can "see" racers use the movements and what I identify as good skiers on the slope use the same movements. Mechanical analysis cannot do this analysis for me or make this descision, mechanical analysis is just a way of describing a movement, whether it is good, bad or indifferent.

Taking a group of racers, as was suggested, for analysis is profoundly flawed. It is more difficult to use a group in this way than one good skier, somewhat counter intuitively. In one skiers race there are repetitions of turns some good some bad and we can if skilled choose one turn over another, based on experience and the empirical evidence. A group of racers will all ski differently so the variation and complexities of analysis of even one turn multiplies.

Who is going to review such a range of complex mechanical outcomes and choose the best outcome? What can the mechanics of the particular outcome tell us? If you do not understand the movement intentions used to generate a particular outcome, looking at the mechanics tells you absolutely nothing. This is true of a single racer and a group of racers. Only experience assists with intentions.

The eye and video are sufficiently accurate to analyse movements. Why do I need to know whether 4 or 5 gs was pulled in a turn, I don't, this level of description tells me nothing of use ~and so on.

In short, can PMTS or any theory of skiing be backward engined from a mechanical study of outcomes, no its impossible. As a system skiing is too open and too complex a system to even make useful comparisons between theories, it requires experience and lots of empirical evidence to develope or compare skiing and skiers.

So much for paraphrasing.
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby oggy » Sun Dec 29, 2013 7:34 am

Hi theorist,

my current understanding of Harald's O-frame shots is that they represent a statement of intent of the skier in a sense. I.e. whether you display the O- or A-frame in transition is probably not that important in itself. That point is really about setting the turn up and the skis are not doing much at that instant, so a few degrees of difference in tipping angles either way probably don't really make that much of a difference. I suspect that otherwise we'd be seeing O-frames in every turn in SL races. Of course, I might be wrong, and we will see them in some future champions.

What I understand is more important is that you would almost never show an O-frame unless you were actively trying to lead the tipping with the inside foot and your alignment was appropriately set up. But you can still show an A-frame even if you are trying to lead with the LTE. Thus even a few O-frame transitions tell you a lot about what the skier is doing.
Last edited by oggy on Sun Dec 29, 2013 8:21 am, edited 1 time in total.
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby Max_501 » Sun Dec 29, 2013 8:00 am

oggy wrote:What I understand is more important is that the you would almost never show an O-frame unless you were actively trying to lead the tipping with the inside foot and your alignment was appropriately set up. But you can still show an A-frame even if you trying to lead with the LTE. Thus even a few O-frame transitions tell you a lot about what the skier is doing.


Exactly.
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby h.harb » Sun Dec 29, 2013 2:31 pm

Oggy, great insight, great posts continue. This comment demonstrates a true student of "Skiing", well done. Another one for the greatest PMTS posts or Quotes of all time thread.
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Re: 3-D motion capture comparison of elite WC SL skiers

Postby jclayton » Mon Dec 30, 2013 12:49 pm

Would the A frame at transition also largely be just a by product of bringing the skis together at transition ? The vertical separation changes to horizontal separation for a very brief period and naturally the knees would tend to move together earlier when unweighted but it disappears in the all important initiation of edge engagement ! Mainly in very fast turns .
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