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Center of Mass - Page 5

post #121 of 138
Well I'm with you Disski, I have to work hard to make what I have go faster. that's okay though, skiing is not just about faster moves. Later, RicB.
post #122 of 138
I want to add one more important thing to this discussion.

Those who read through my paper skier demo will now have an understanding of the lateral balancing challenges skiing with square hips present. The demo explains how and why square hips limit the ability to move the CM laterally while on a given edge angle.

The detrimental consequence here is that if balance is to be achieved at high edge angles with square hips, some other means of moving the CM laterally, outside of hip angulation, must be employed. The only other meaningful option available to the square hipped skier is angulation at the knees. In reality, this is a very productive means of achieving lateral relocation of the CM, much more productive than hip angulation. The problem is it's an inherently weak postion. Strength is found in structural alignment. When gross angulation occurs at the knee a weak link is created in the bio mechanical chain. The muscular system is unduely taxed, and the knee joint is put in unnecessary jeapardy.

At high speeds and low edge angles, on small radius skis, severe angulation at the knee will not be as needed to achieve some form balance, and therefor will not be as apparent to the observer. The skier may end up over pressuring the inside ski, but he will still be able to execute.

But,,, watch a square hip skier attempt to achieve high edge angles at slower speeds and you'll see knee angulation quickly emerge into shockingly clear and ugly view. This is where, from a balance perspective, the efficiency of the technique breaks down, and where the practicality of square hips comes to a screaching halt.

There are reasons WC'ers counter the hip, and this is one of them; it allows for utilizing the structural strength of a long, relatively straight leg. For the recreational skier attempting to learn to make high edge angle carves it's even more crucial because of the slower speeds at which they execute, and the greater lateral CM displacements those slower speeds require to acheive balance.
post #123 of 138
aaaah & that is why my brain screams out "no" every time someone says to angle the knees... or edge with the knees... it just feels wrong...
post #124 of 138
I agree Rick. I think this is evident when I see short carving arcs that have a separation between them.
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The skier is loading up the skis with too little structural integrity and cannot manage the pressure at the end of the turn which causes an explosive rebound that kicks the skis off the snow. Quite often this skier will be using knee drive side to side to edge the skis with too little range of motion in the ankle knees and hips which would allow a more structural stance. Later, RicB.
post #125 of 138

Bode

Watching the technical events at the Worlds at Bormio I did not see too many racers square their hips. Bode does though. Not to his advantage it seems right now as the results show.
post #126 of 138
I watched some the races too Biowolff. Skiing through counter was very evident as a theme, and the best skiers had a nice long outside leg in the middle of the turn also. Bode didn't have his slingshot working did he? Later, RicB.
post #127 of 138
Sorry that it takes me a few days to get back to the forum. (Too busy skiing every day.)

Nolo, sorry to ‘invalidate’ your question. The outcome of the discussion is pretty good though!
Maybe I am just too much of a stickler when it comes to correct terminology. And our Center of Mass (or Balance Point for that matter) isn’t a body part. And it is not necessarily around our navel area either. Just imaging a gymnast sitting on the floor, legs extended, hands on the toes, chin on the knees, upper part of the body touching the thighs. The CoM will be somewhere at the chest area. (Have a picture, but don't know how to upload into this system.)


RicB, I totally agree with your statement: "How effectively we move our core over our skis relative to the forces at large is skiing. What was your point Little bear?"
I think I made my point by stating that the original question was flawed. The CoM can not tip the feet.

If we use the terminology: "move the center of mass into the turn" we use an effect of a movement to describe a desired outcome. However, it does not describe the cause of the movement.

I know a lot of instructors use CoM or hip- or pelvic area synonymously. As stated in my previous comment, that is incorrect. But even if we want to accept the erroneous terminology, we still should explain to our clientele how to move that area. To move the pelvic area you must use another body part. Example: if you would build a robot that is supposed to kick my behind with its foot, it doesn’t help to tell the robot’s foot to do so. You will have to program the robot’s circuitry to use the hip flexor, hamstring, quadriceps….etc. to go to work.

So, if we use the term: move the CM into the turn, we should also talk about the movement required to do so. And there are lots to choose from.

Little Bear
post #128 of 138
If you are linking turns, you only need to do something to "cause" the (center of the) body to "move" into the next turn if you fail to "release" the forces deflecting it away from the center of the next turn when it's momentum wants to go there. At that point, the crux of effeciently linked turns, relaxing (or even retracting) the legs just prior to releasing/changing the edges is all it takes. Miss this "window of opportunity" and you'll need to create some other combination of less efficient compensating movements to re-direct the (center of the) body from it's path toward the woods back down the hill.

I prefer to guide the learning of just enough, at the right time, to needing any of the myrid of too much too late catch-up options.
post #129 of 138
Thread Starter 
Point taken, Little Bear.
post #130 of 138
Littlebear, I couldn't agree more about giving our students the how, the movements needed to ski and their relationships to one another and their effect on the ski snow interaction. Just felt I wanted to hear more. Later, RicB.
post #131 of 138
Quote:
Originally Posted by Rick
The detrimental consequence here is that if balance is to be achieved at high edge angles with square hips, some other means of moving the CM laterally, outside of hip angulation, must be employed. The only other meaningful option available to the square hipped skier is angulation at the knees. In reality, this is a very productive means of achieving lateral relocation of the CM, much more productive than hip angulation. The problem is it's an inherently weak postion. Strength is found in structural alignment. When gross angulation occurs at the knee a weak link is created in the bio mechanical chain. The muscular system is unduely taxed, and the knee joint is put in unnecessary jeapardy.
As usual, Rick (A) great observations, and (B) I agree with you.

And, as usual, let me add my 2 cents:

1. Knee angulation still has a role in ski racing, particularly in slalom. Knee angulation is one of the techniques for skiing a flush successfully, where the quickness demanded--and need to keep the CM centered and moving as straight as possible--makes knee angulation one of the appropriate tools in the tool box.

2. Despite the outside leg straight mantra about high-level racing, you actually see in pictures of GS racing a slight bend of the outside leg, with the knee pointing in the direction of the inside of the turn (aka, knee angulation): This increases edge angle and allows more pressure on the inside edge (and the forebody) of the outside ski.

3. Given that, at times, skiing puts demands on our bodies in this way--the lateral collateral ligament and medial collateral ligament being put in a somewhat stressed position by knee angulation--it seems to me that this is something we should work on in dryland preparation. (The one piece of advice I carried away from tearing my MCL about nine years ago, was to trengthen all the muscles around the knee to help avoid a recurrance.) The one exercise I do that recreates these demands is to do haybalers on a Bosu (flat side up--you can also use a bongo board, which is more challenging) taking a medicine ball or light weight and with both hands and holding it, with deeply flexed and angulated knees, off to the right of my right ankle, then straighten while lifting it to hold it to the left of my head. After X repetitions on one side, without a break, do X repetitions on the other side, then step off the bosu with shaking legs. In my view, this exercise is probably as good as anything I do in the gym as an exercise that crosses over to skiing, since (A) it's the only thing that makes demands on knee angulation; (B) it has a balance/core aspect; and (C) it works the legs like skiing, working against a load while balancing at the same time. Because it's such a nasty leg exercise, I do it with a relatively light weight and do it near the end of my workout, since IMHO but contrary to dogma among exercise books, what we skiers need is balance practice when our legs are tired, since that's when our balance will be tested in the real world (end of the race, or run late in the day.) Of course, like anything else you read on-line (or anywhere) you need to figure out whether this exercise makes sense given your current fitness level and balance skills and need to listen to your body about whether it feels OK--it does (like knee angulation on the hill) stress the collateral ligaments.

(With embarassment, I add that #3 in this post is tangentially relevant to the original topic of this thread, discussion of CoM direction, since the whole point of haybalers is to manage lateral balance while transferring a weight from low on one side to high on the other side. One way to do that is by knee angulation, since that directs the rest of the body's mass away from the direction the medicine ball is transferred to when it's lowered to the outside of the ankle.)

SfDean

PS: Biowolf, I agree with you that some amount of counter is probably a necessity for strong skiing, and that you see it on the World Cup almost ubiquitously. (But the counter you and I see is someone else's "body facing down the fall line" as racers complete the turn at gate clear. As if that were something different.) But the issue is really one of degree--your skiing (and RicB's and a lot of other people's here) is almost certainly more refined and advanced than mine, and I have a tendency to see specific techniques as tools to throw at certain problems I encounter. So when I talk about "counter" you should probably substitute "really exaggerated counter".

So, I use exaggerated counter in GS when it's icy and rutted and I want to throw an even greater edge angle at the problem, like a big wrench thrown at a stuck pipe connector. That exaggerated counter has to be coupled with an inside foot pullback or it quickly becomes the problem of excessive inside tip lead which makes it difficult to pressure the shovel of the inside ski and maintain lateral, forward balance through the turn. I find that grossly exaggerated counter too slow in slalom gates, which is not the same as saying strong skiers don't show some counter even in slalom.

By the way, kudos everyone--this has been a really interesting discussion.
post #132 of 138
Quote:
Originally Posted by Rick
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The detrimental consequence here is that if balance is to be achieved at high edge angles with square hips, some other means of moving the CM laterally, outside of hip angulation, must be employed. The only other meaningful option available to the square hipped skier is angulation at the knees. In reality, this is a very productive means of achieving lateral relocation of the CM, much more productive than hip angulation. The problem is it's an inherently weak postion. Strength is found in structural alignment. When gross angulation occurs at the knee a weak link is created in the bio mechanical chain. The muscular system is unduely taxed, and the knee joint is put in unnecessary jeapardy.



.
Ric:
Since this has been a very civilized discussion I throw my caution to the wind
and play the devil's advocate. Could it be that there is an other option available to the square hipped skier, this being the loading of his uphill ski and the edging of the inside edge of the uphill ski ? I read recently that in Tai Chi
moves resembling knee angulation are none existant where else moves of the knee to the outside are abundant. How about that ?
post #133 of 138
Quote:
Originally Posted by Biowolf
Ric:
Since this has been a very civilized discussion I throw my caution to the wind
and play the devil's advocate. Could it be that there is an other option available to the square hipped skier, this being the loading of his uphill ski and the edging of the inside edge of the uphill ski ? I read recently that in Tai Chi
moves resembling knee angulation are none existant where else moves of the knee to the outside are abundant. How about that ?
Biowolf, if you are adressing this tai chi question to me then I would agree that knee alignment is critical in good practice. Knee problems in tai chi seem to be a U.S. phenomenon. On the other hand double weighting is a position of weakness in tai chi. Always has been and always will be. Later, RicB.
post #134 of 138
To the participants of this thread,

During training sessions we have been watching video of Miller. With the tape running very slow and in some cases, frame by frame, it is evident that he is rotating slightly before the transition and then extending through transition. At the point of transition, (four edges on the snow) he is square, but shows some counter through the end of the turn. He doesn’t seem to show any major counter through the end of the turn, but it might seem that way in a still picture because of the rotation that we observed in the transition to start the new turn.
IMHO, I believe that a skier should strive to be equally weighted to at least the fall-line. Both skis will be tipped up on a high angle and there will be a lot of pressure on both skis because of deflection and redirection of the skis. And again, the skier should try to distribute the weight equally between the two skis. The skier should try to be square at the fall-line and have maximum inclination at this point. As the skis come through the fall-line, the skier should feel weight increasing on the outside ski. This is not to say that all the skiers’ weight should be transferred to that ski, but that there will be an increase of weight to that ski. This I believe is acceptable and the skier should try to manage the pressure. As the turn develops through the fall-line, the skier should try to remain as square as possible until the new transition approaches. There will be some tip lead that develops because of speed and pitch of the terrain, but the skier should still strive to remain square and not let the counter that develops become excessive.

In the transition is where we are observing that there is slight rotation with Bodie, and IMHO, is where some in this discussion are seeing what they observe as being counter in some of the WC racers. I do agree that in some of the WC racers there is counter, but in the good ones, they try to remain squarer to the skis with their hips, and ski to slight counter is our observation. Bodie seems to rotate slightly in the transition and then relaxes the downhill leg, and then move through neutral and extends, where the whole process starts again.

I want to express that these are high performance turns and that with our students, to see these moves being preformed in a dynamic way might not occur until they are at least a level 8. But that doesn’t mean that we as teachers shouldn’t try to teach in this direction to all of our students. Anyway, this is the way I see it and this is what we are working on in our training. I and my fellow trainees feel that it’s the right direction and I am excited about what it’s doing for my skiing. -------Wigs
post #135 of 138
Quote:
Originally Posted by Wigs
To the participants of this thread,

During training sessions we have been watching video of Miller. With the tape running very slow and in some cases, frame by frame, it is evident that he is rotating slightly before the transition and then extending through transition. At the point of transition, (four edges on the snow) he is square, but shows some counter through the end of the turn. He doesn’t seem to show any major counter through the end of the turn, but it might seem that way in a still picture because of the rotation that we observed in the transition to start the new turn. -------Wigs
Thanks, Wigs, for that insight. What does your slow motion analysis of Bode Miller show about his hip position, which seems quite different late in the turn compared to other World Cup skiers? Bode Miller's GS runs are very easy to pick out on the USSA "Winning Runs of the World Cup" DVD even with the sound off, because his hips are so far back late in the turn/early in the transition. (Between that and the inside hand skimming the snow, after Soelden one of the Austrians sniffed that if Bode Miller keeps winning, "all the young Austrians will start skiing like snowboarders".)

My theory was that Bode Miller's hips back helps with a faster transition, since his upper body/lower body is a shorter pendulum and thus pivots faster through a shorter arc as he crosses over. It may also be a function of his great fore-and-aft dynamic balance (which, in any event seems required by his skiing style, which may exceed even his balance capabilities on short slalom skis) where his CoM takes a much shorter line between gates while the feet move faster but take a less direct line, thus getting ahead at points before the CoM catches up.

What does your slow motion analysis show, and what are your thoughts?


SfDean
post #136 of 138
Quote:
Originally Posted by Wigs
,

IMHO, I believe that a skier should strive to be equally weighted to at least the fall-line. Both skis will be tipped up on a high angle and there will be a lot of pressure on both skis because of deflection and redirection of the skis. And again, the skier should try to distribute the weight equally between the two skis. The skier should try to be square at the fall-line and have maximum inclination at this point. --Wigs
Wigs:
I highly respect your opinion and your willingness to experiment. I also have the feeling watching WC that there is a new tendency to weigh the inside ski more. But I think it happens later in the turn. Loading the inside ski before the falline would stop us from reaching maximum inclination, I think. (I will stop using "I think" from now on. What I am trying to say is that the opinion expressed is my personal view and I make no claim of certainty). Before the falline it is important to shorten the inside leg to get the CoM downhill. At that stage because among other things the change of ski lead and stance there also will be counter (Bode doesn't counter here, he rotates and it is a mistake) Later on in the turn as pressure builds and the edge angle increases the inside ski is pressured more (combined with less counter) untill the initiation of the float by pushing off the inside ski (which would mean all the weight on the inside ski for an instant). The float sets the hips free to establish the new counter (again, Bode does not do that at the moment).
Again, this is my personal view and I am still experimenting with it.
post #137 of 138
[quote=sfdean] My theory was that Bode Miller's hips back helps with a faster transition, since his upper body/lower body is a shorter pendulum and thus pivots faster through a shorter arc as he crosses over. It may also be a function of his great fore-and-aft dynamic balance (which, in any event seems required by his skiing style, which may exceed even his balance capabilities on short slalom skis) where his CoM takes a much shorter line between gates while the feet move faster but take a less direct line, thus getting ahead at points before the CoM catches up.

What does your slow motion analysis show, and what are your thoughts?

Sfdean,

We must be watching the same video. I think you are right on in your observations. What we are trying to do in watching WC skiers on video is to apply some of these techniques to our own high performance skiing. We hope that in our own skiing we can smooth it out a bit and not be as radical as Bodie and others on the World Cup Circuit are coming down a race coarse. But still, the WC skiers are changing the way we teach and ski, no? So this said, I don't think that we should allow our hips to drop so far back just before the transition like Bodie does when we are just out making some turns.-------Wigs
post #138 of 138
Wigs, wish I had more time to respond to your post, but I don't so just a quick one.

I find it perplexing that you would not recognize the counter being used by WC skiers at the apex of GS turns. It's evident in almost every instance. I wonder if your observations are influenced by what you desire to see. Perhaps someone can post a few WC GS shots that we can inspect and discuss.

And, as to your equal weight theory; check out the edge angle of the inside ski as compared to the outside. Very typically the inside is lesser. If weighted equally and carving the skis would cross. If the inside were being steered to compensate there would be considerable drag with such high loads, and would be difficult to steer. And if equally weighted the severely flexed inside leg would be stuggling to bare the load.

And the rotation you see; was it displayed in a turn that incorporated a pivot? This is the postion that drives redirection, and it's a result of the counter in the prior turn.
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