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Yet another angle on Rotary - Page 2

post #31 of 39
Quote:
it's not always the bio accuracy of the feedback from the coach that makes it valuable to the student, it is the light it turns on in the kids head
Very well said, FastMan! Discussions such as this one should NOT be confused with teaching skiing. I feel for the poor student trying to apply some of the technical thoughts here!

The mechanism you described is still counter-rotation. The upper body winds up, then, when you relax your muscles, it unwinds, aligning the feet and skis with the upper body. Something must oppose this action. The upper body doesn't need to counter-rotate much, as I described above, because of its larger mass and "moment of inertia." But it DOES counter-rotate.

Unless the windup is followed immediately by the unwinding, in a non-stop "one-two" action. In this case, the mechanism is "rotation."

Or unless you stabilize the upper body with a pole plant, preventing it from counter-rotating as the feet turn--in which case the mechanism is the Blocking Pole Plant ("wrenching").

What you've described, very well, is "anticipation-release." It is not a separate rotary mechanism, but it can serve to strengthen any of the rotary mechanisms I've described. Like a baseball pitcher winding up before throwing the ball, or stretching a rubber band (anticipation), prestretching muscles strengthens their response.

Best regards,
Bob Barnes

[ January 18, 2003, 07:36 AM: Message edited by: Bob Barnes/Colorado ]
post #32 of 39
I should add, by the way, that all this does not negate the value of practicing balancing on one ski. It's a great balancing exercise. But instructors must be aware of the risk of introducing very bad habits when trying to TURN on one ski. Practicing balancing on one foot, and tipping that one ski--either directly or by tipping the OTHER ski to start the appropriate chain of movements--is an excellent and important exercise. (It's still an EXERCISE, though--not SKIING!)

I repeat, whether it's a byproduct of a tipping action, or an intentional pivoting action, actively turning one ski while lifting the other MUST involve countering actions or rotation ("1-2") in another part of the body, or a blocking pole plant. While they're all important skills for skiers to master, essential for versatility, all these are bad habits, and all cause the tail to twist out, however subtly!

Lifting one ski limits your options for turning to pure carves (tipping and pressuring, not steering), or tails-out skids with rotary impulse originating in the upper body. Yes, it can be very subtle--"not TOO bad"--but it's still usually a mistake!

Finally, none of this suggests that you need equal weighting of both skis. To steer with your legs, you simply need to have sufficient contact of the inside ski to provide the small resistance needed to turn the other ski against (archaically known as "fulcrum assistance" of the inside ski).
post #33 of 39
Thankyou Bob Barnes - for explaining why skiing on 1 ski feels SOOO diferent to making turns on alternate skis - whichever edge.
post #34 of 39
Arc,

I don't take it as picking on me. More like correcting me. You are 100% correct that the kinetic chain starts at the end of the chain - the feet. I was generalizing and being lazy. However, that said, (and as you have already mentioned) the feet can't move in isolation for all this to work. They have to pull the knees into the chain, which, by doing so, rotates, the femur. I was just stating the visually obvious, that when the knees start to move, the femur will rotate. So much for trying to keep the word count down.
post #35 of 39
Quote:
Originally posted by Bob Barnes/Colorado:

A rotary movement, regardless of it's intent, is still a rotary movement. Let's not confuse the various combinations of specific muscles and movements that can be used to turn the foot with the underlying physical principles--that I described above.

It is certainly true that tipping a foot involves rotation of the femur, as does turning the leg--it creates torque ("rotary force"). Just because you didn't MEAN to turn it, though, doesn't change the important outcome--a rotary movement by any other name is still a rotary movement! And for every action, there is an equal and opposite reaction--for every torque, an equal and opposite torque. Something has to move the other way, or provide resistance to allow the movement. This point is not debatable, by the way--you either understand it or you don't.

As far as rotary mechanisms are concerned, turning the foot as an indirect result of a focus on tipping it is no different from turning it as a result of directly focusing on turning it. Physics is unconcerned with your intent! Both involve torque, and both entail an equal and opposite reaction. Somewhere.

Best regards,
Bob Barnes
Bob,
I know you were responding to the specific development of this thread but it seems to me that some will take statements like "a rotary movement by any other name is still a rotary movement!" and "Physics is unconcerned with your intent!" as absolutes.

From my perspective they are anything but. A rotary move that a skier learns to do without any perception or awareness of rotary is very different from one in which they learn to do the move by specific intent to rotate a joint. Similarly, physics may be unconcerned with human intent but human perception and motor learning are integrally linked and sometimes (even at the very highest skill levels) can be totally unconcerned with the physics or biomechanics of a movement.

It seems to me that one of the greatest values of this forum is the ability for skiers and instructors alike to share their experiences. Certainly "Joe Blow" skiers (like myself) may have limited experience but if somethings works for us perhaps it will raise awarenenss for others. Of course an instructor may be able to speak from a far greater base of experience but they are only human. Many clearly have their own biases which may limit their objectivity in evaluation of various approaches.

We all search for effective ways to learn and teach. From my observation no one has a patent on these, rather they vary from person to person and are scattered between all the varied experiences we see reflected here.
post #36 of 39
Si:
Quote:
I know you were responding to the specific development of this thread but it seems to me that some will take statements like "a rotary movement by any other name is still a rotary movement!" and "Physics is unconcerned with your intent!" as absolutes.
Yup, I take it as absolute. The five kinds of rotary are a definition and do not distinguish between active rotary and passive rotary.
Quote:
It's like saying "my car is out of alignment--pulls to the right--so I don't have to steer
Bob addresses pasive and active with this little sentence.

I certainly distinguish between passive and active movements but passive and active can be more than just for rotary movements and therefore should enjoy their own definitions.
post #37 of 39
Pierre,

I think you're being argumentative. The physics, biomechanics, and kinematics of skiing are clearly important. However, it is critical to also recognize and address perceptions and motor learning abilities (and disabilities). My point was to say that to approach learning or teaching of skills exclusively from a movement analysis perspective is bound to be far less than optimal for many. I don't think that was Bob's intent but his post came off to me as being interpretable in this way. I hear some very successful people (instructors and skiers) saying that rotary is a very critical part of all levels of skiing. I hear other successful people saying that while rotary occurs, an (improper) emphasis on rotary movements can be an impediment to improvement.

It would be nice to be able to avoid different people's version of the gospel and hear more about their experiences and discoveries.
post #38 of 39
Quote:
I hear some very successful people (instructors and skiers) saying that rotary is a very critical part of all levels of skiing. I hear other successful people saying that while rotary occurs, an (improper) emphasis on rotary movements can be an impediment to improvement.
Si--anyone who doesn't say BOTH of these things is quite clearly missing a vital point. An improper emphasis on ANYTHING is an impediment to improvement!

And apparently, you also missed another very important comment of mine:

Quote:
Discussions such as this one should NOT be confused with teaching skiing.
I'm not sure how that statement could be misinterpreted as you suggest. This IS a discussion of the mechanics of skiing--the technical aspects. How these things are taught is quite another matter, but without a clear understanding of the subject, no teacher, no matter how brilliant, can do it right!

Little is more frustrating for a student than discovering that they've been well-taught all the wrong stuff.

Best regards,
Bob Barnes
post #39 of 39
Well and succinctly stated Bob. Your disclaimer not withstanding I (and other readers?) attempt to understand the relationship between the mechanics of movements and learning of movements. My initial post in this thread was focused pretty exclusively on the learning aspects with the expectation that the mechanics would readily be brought into play by others. I think that is what motivated my comments here, the desire to have people (like yourself) talk more about your experiences in teaching and/or learning movements along with descriptions of the movements themselves. As you said "Discussions such as this one should NOT be confused with teaching skiing," so lets talk more about the relationship of this to teaching skiing.

For all the discussion about rotary and tipping here I still am not very clear how others (perhaps except for Ydnar, who I had the pleasure of skiing with for a day early this season, and Arcmeister, who has more specifically addressed this) approach the order or emphasis of these with various skiers.
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