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What are the basic core movements of skiing - Page 2

post #31 of 57
Good points in all that.

If one really needs to have the pressure expressed in a percentage, good luck with that. It is way too dependend on a given situation, so I would never really express the distribution of the weight/pressure like that. Changes just too much and would focus more on the stance.

Also the graphic is a bit dated. It is also not clear if the bottom is actually the top or vice versa. It would certainly also be more expressive if you can see the combination of two turns.

It certainly is true that the turn is not round, but oval. Ideally not at the top and not at the bottom, but at the apex. But of course it depends on the situation and very much on the skill of the skier. But since we all want to achieve the best scenario I thought I just mention that.

Quote:
Originally Posted by GSS View Post
In reply to tdk6:

Pressure may be decresing after apex but its not because the forces would be decresing. Its due to other facts like the excellent comment that the turn radius is not even, it opens up after apex. If you were holding on to the same turn radius after apex I think you would agree with me that pressure would increase (if everything else was unaltered).”

If you hold the SAME turn radius after the apex, the pressure will be the SAME if everything else is unaltered.

“At apex you have centrifugal force and gravity pulling in 90deg angle between themselves. Centrifugal force pulling you perpendicular to where gravity is pulling you down the slope. As you come through apex this angle is getting smaller and three quarter through the turn they are pulling in 45deg angle.”

Please clarify - I do not understand 45degrees. I think it depends on the shape of this part of the turn.

“In other words more forces pulling you away from origo, center of turn. Because this happens your turn radius opens up and you also at this stage relese the turn so less pressure is present.“

The main reason the turn radius starts to increase after the apex is that the skier is 'retraction un-weighting' with both legs, while simultaneously reducing ski edge angle. This causes the skis to bend less, and so the instantaneous turn radius increases.

“Also, you are right that dropping the CoM in the high C does not decrease pressure, the pressure is increased and vice versa after apex. I stand corrected. This is due to the tention build up caused by angulation. However, as you incline in the high C you are moving your CoM in the direction of gravity. This will lessen pressure.”

I agree that moving the COM in the downward gravity direction can cause the pressure component in THAT direction to decrease, but the pressure due the centrifugal force is so much greater at the apex (with typical GS turn edge angles). The lowering COM effect just slightly slows the pressure build in the turn due to the centrifugal effect.

“After apex as you de-incline you are again moving your CoM in the direction and thus lessen pressure. Extending the leg is annother story. Since you are extending in the opposite direction of centrifugal pull (if we skipp gravity for a second) you will move CoM away from pull. This will increase pressure. And vice versa. Also note that at apex we are no longer dropping our CoM. It has stopped dropping causing a peak of pressure.”

The pressure on the ski at the apex has almost nothing to do with raising and lowering the COM in the direction of gravity. At high edge angles, pressure on the ski is almost entirely due to turning radius.

“Also if you look at racers you can see snow spraying from their skis after apex. I dont know why you think that a pure centrifugal force is greater than a combined centrifugal force and gravity together. I feel it every time I ski.”

The forces in a 60degree edge angle are gravity acting straight down, and two times gravity in the centrifugal/centripetal (outward) direction. The effect is to load the skis with 2.2X gravity. In high level (world cup) racing, and hopefully in high level recreational skiing similar to that we teach, the snow should start to spray above the apex and stop at the apex. It is a sign of a poor turn if the snow spays below the apex. See the photo of Rainer Schoenfelder in a GS turn, and an Aspen ski teacher captured at the apex.



“I think that you have not been paying attention to what has been discussed. It was never claimed that there would not be flexing and extending and that the inside leg would not be flexed at any time. You give that impression in your post. On the countrary, it is being flexed very much. It should. Otherwise there would be no turning. Long leg/short leg. What I have been saying is that the outside leg that is carrying the load is being extended at all times.”

I assume you mean the outside leg is extended near the apex. In WC GS racing the outside leg is straightest at 1/4 of the turn (apex being 1/2 the turn) – see the picture of Schoenfelder. The knees/ankles are flexed more-or-less the remainder of the turn.

“These are general observations. If you dig a bit deeper you will find that the leg gets flexed a bit at apex as forces hit in but mostly that is just to be able to extend and hold a proper edge. The gross movements are one leg extended at all times, both at apex. It looks like that is the whole intent of their skiing at that particular run.
One more thing, you are saying that the inside ancle is being flexed as the leg is flexed to max. If the ancle is being flexed aggressively like you suggest it also means that there needs to be a lot of pressure on that ski. Is this what you are suggesting? Lots of weight and pressure on the inside leg?”


Yes, take a look at Maier and Cuche.

There is almost as much force on the inside ski, as is on the outside ski - evident by the bend in the skis, and the snow spray. Notice the last frame of Maier, where the outside ski has only the tail engaged.

Here is the ideal distribution of ski pressure in a WC GS turn: (from Greg Gurshman)


I also see Herman's and Didier’s inside ankles have some flex in the gate.


“There is also annother explanation why the knee is being pushed in under the arm pit. Its because the skier is flexing at the hip forward quite a lot. Actually the ancle has nothing to do with it. Its a simple question of your femure and your upper body folding up. Also, why are you saying that the outside leg is completely extended at apex when knee is pushed in under chest?”

Yes, I see some of this in the Maier photo, but there is still inside ankle flexion and weight on the inside ski.

“ I thaught you were saying that the outside leg should have been flexed at this point in the turn since flexing would create more pressure.”

Sorry if I was not clear, look at Herman's and Sheonfelders outside leg at the gate - I see a small flex.

This whole turn thing is more complex than the above comments would suggest. The distribution of pressure for a WC GS turn is shown below. It is the classic 'comma' turn. (Diagram from Greg Gurshman).



The width of the carve in the diagram indicates the pressure. Most pressure is on the outside ski in the first 1/4 - 1/3 of the turn (as in the table above) - this is where the most snow sprays, the overall forces on the skis are greatest, the outside leg is the straightest, and the instantaneous turning radius is smallest (not at the apex). At the 1/2 point (the gate), the skis are getting close to being evenly weighted. In the bottom (3/4) of the turn the inside ski is weighted most.

Sorry this is departing from the original thread topic, but I wanted to add my comments on tdk6’s post.
post #32 of 57
simplyfast:

The turn diagram has the first part of the turn at the top. As I understand it, the highest forces are above the gate. Also the highest speed is above the gate, due to the run out from the previous gate, thru the turn transition.
post #33 of 57
For that graphic, downhill is down the page.
post #34 of 57
Thread Starter 
GSS, thanks for your indetail posting. Here is a demo you can do at home. Take a one-two meter long rope and tie an object to one end of it. Start swinging the rope horisontally. Only the centrifugal force is acting upon the CoM of the object away from the center of the circle. Gravity is pulling the object down towards earth middle. The tention in the rope is even and the object circles smoothly arround in a circle. Now start to bring one end of the circle down towards the ground. What you are now feeling is more tention and pull as the object comes down closest to the ground and on its way up. This is no different than the centrifugal and gravitational force acting upon a skier. How long you are holding on to your turn is then a matter of tactics. If the gates are set with great offset then you need to hold on to your turn longer causing the pressure buildup to be delayed untill after apex. The photos you are showing are displaying situations where the case is the opposite.

Im familiar with Gregs articles. However, the image of the tracks in the snow is not entirely true since it doesent take in count the total pressure only displays how pressure is transfered during the turn. Its a different thing. There is hardly any pressure in the top part and increasing towards apex and then depending on how far across you need to finish your turn the pressure starts to decrease after apex. The animation merely shows you that you should start with outside ski pressure and end up with inside ski pressure. Not a universal fact for all turns just way of learning movements used for gate racing. There has been made great studies of how the pressure is distributed. We need not to guess. Here is one good link:
http://www.youtube.com/watch?v=qOMcNWgiT_A
post #35 of 57
The swinging object analogy does not apply, since the turns being discussed are not round.
post #36 of 57
Quote:
Originally Posted by GSS View Post
As I understand it, the highest forces are above the gate.
Are you sure? Please explain.
post #37 of 57
Thread Starter 
Quote:
Originally Posted by BigE View Post
The swinging object analogy does not apply, since the turns being discussed are not round.
We are not discussing any particular shape of turn. We are talking about core movements. We have been sidetracked here but GSS is probably right that the most pressure is happening at apex. Or lets say it should if we want to go fast. I was thinking of a slightly different scenario where we ski to controll our speed and try to end our turns slightly more across the hill than what the WC skiers are doing in the free skiing video. My fault. I should have defined it more accurate.
post #38 of 57
Nice discussion, guys. I'll just throw in a renegade thought for now. The lowering of the Center of Mass does not necessarily increase centrifugal force. Consider a tuck. More-so, the lowering of the CM is a needed response to the increasing centrifugal forces created by a lessening turn radius. Doing it directs the ground impact point of the force vector acting on the CM to the desired point of balance,,, generally close to the outside ski. How low you have to drop the CM depends on multiple factors,,, the major ones being speed of travel and side cut of ski. In the old days of carving, big edge angles were associated with much higher CM positions than today. Knee angulaton had great merit and need.

Now carry on with this excellent discussion.
post #39 of 57
Another sidebar:

If you look at Gurshman's pressure distribution graphic that GSS posted here, what stands out is that this is the very same pressure distribution that would be present in an "early weight shift turn".

This turn encompasses four transitions that we all know and love:

1) Outside Leg Relaxation (OLR).
2) Inside Leg Extension (ILE).
3) The "Super Phantom Move(tm)".(Lift and tip) which becomes
4) The "Phantom Move(tm)" (Lighten and tip -- phantom since you can't see it.)

OLR and the "Phantom Move(tm)" would be very close, as would ILE and the "Super Phantom"(tm). ( Some small differences in execution.)

(tm) by Harb Ski Systems.

If these 4 transitions are indeed examples of the "Early weight shift turn", then early weight shift is a core movement of expert skiing.

More on this here:

http://forums.epicski.com/showthread.php?t=19753

Be wary of the difference between weight and balance. Sometimes balance moves along with the weight othertimes not....what matters is the exit line of the CM.
post #40 of 57
I am sorry for diverting the original thread "What are the basic core movements of skiing" to where we are now. I think we got into this looking at carving turns done by WC racers; and the thread was started by tdk6.

I have been discussing GS turns made by WC racers. Most of us, including me, do not come close. As ski instructors, we in the USA (PSIA) try to achieve and teach dynamically balanced, EFFICIENT skiing. We teach the Skills Concept (ERP with ODDIRT - PSIA speak).

In racing the goal is to ski down a slope, around a course of gates, in the shortest time. Racers expend much energy doing this, and experience forces on their bodies that I can only imagine.

My understanding of a WC GS turn in 'tight' gates (no delays. etc), is that most of the turn is above the gate. I define apex as the point of 'sharpest' turning, or the minimum instantaneous turning radius. For most of us, this is at the gate, if we are lucky!!.

Take a look at Rainer in the photo. Most of his change in direction is behind the gate in the photo. This is the apex of his turn. Physics requires that this fast change in direction coincides with the smallest instantaneous turn radius, and the highest centrifugal force/pressure (on his skis). The snow spray is indicative of the pressure on the skis - it is all over before the gate. The highest pressure on the skis is above the gate. This does not mean that there is not considerable pressure on the skis at the gate; just that it is diminished. It is hard to see, but look at the bend of the skis in the third frame from the end (at the gate) - there is still pressure there. But, the last two frames have the skis much straighter - the pressure is very much reduced. Rainer is going almost straight in the last three frames - his turn is over - his is gaining speed. This is what I mean by a 'comma' shaped turn.

I will agree with BigE about tdk6's whirling rope.

tdk6's video form Massey University in New Zealand is very interesting. Take a look at the same skiing sequence showing the X-Y-Z views of the skier, and most telling, the video.



The person used for this demonstration appears to me to be a competent 'club racer' skier. It's only possible to see the last couple of turns, but he is completing his turns below the gate. This type of turn will have the major pressure on the skis at, or below the apex. It's not fair to compare this to a WC level racer.

TDK6's quote "There is hardly any pressure in the top part and increasing towards apex and then depending on how far across you need to finish your turn the pressure starts to decrease after apex." is correct for a competent skier, but in my opinion does not apply to WC skiers.

I think that most of us should start our turns earlier than we do - most of us are late. As PJ (Jones) says: "You can never start your turn early enough". We should try to get closer to what these WC guys and girls do.

Now perhaps we should get back to the four or five core concepts of skiing.
post #41 of 57
BigE got his post up while I was putting mine together.

I think with the words of wisdom from Arcmeister and Bob Barnes (from the link on BigE's post) regarding early turn initiation are incredibly insightful.

I don't believe that early turn initiation is a 'core movement', just as timing is not a core movement - early turn initiation is a very important technique/timing thing.
post #42 of 57
No I think it is just fine to venture into a different topic. It is all related in a way. I see all these different posts and looks there is really progress in all. Hey how about my idea with the rubber band instead of the rope. And instead of "bringing the end of the circle to the ground, why not at 9:00 or 3:00 O' Clock? I think then the experiment does come really close to the skier. Also the shape of the turn/curve. Again watch your head if you really plan on doing that.

I also dare to suggest actually that the centrifugal force is biggest at the apex and right after that gravity will kick in and then combined those forces are at the highest. (A skier will fall also in that section of the turn, not in the upper portion).
Also a "tourist" will show you easily where the forces increase as he starts to skid out the rest of the turn.

Ski Instructors are many times the better examples, because they ski at moderate speeds. Zooming down an icy hill will cause even the most skilled skiers to make errors, that is why pointing at a WC Skier is many times not a good choice of demonstrating the techniques.

And it is the most ideal situation to turn at the apex, merely because it will allow you to ski the most possible and direct line and also it keeps the "angle of attack" as steep as possible. Turning high up on the gate or "late"makes you ski uphill to the next gate. At that point it may make more sense to switch to a Cross Country gear. Ok, just kidding.




Quote:
Originally Posted by GSS View Post
I am sorry for diverting the original thread "What are the basic core movements of skiing" to where we are now. I think we got into this looking at carving turns done by WC racers; and the thread was started by tdk6.

I have been discussing GS turns made by WC racers. Most of us, including me, do not come close. As ski instructors, we in the USA (PSIA) try to achieve and teach dynamically balanced, EFFICIENT skiing. We teach the Skills Concept (ERP with ODDIRT - PSIA speak).

In racing the goal is to ski down a slope, around a course of gates, in the shortest time. Racers expend much energy doing this, and experience forces on their bodies that I can only imagine.

My understanding of a WC GS turn in 'tight' gates (no delays. etc), is that most of the turn is above the gate. I define apex as the point of 'sharpest' turning, or the minimum instantaneous turning radius. For most of us, this is at the gate, if we are lucky!!.

Take a look at Rainer in the photo. Most of his change in direction is behind the gate in the photo. This is the apex of his turn. Physics requires that this fast change in direction coincides with the smallest instantaneous turn radius, and the highest centrifugal force/pressure (on his skis). The snow spray is indicative of the pressure on the skis - it is all over before the gate. The highest pressure on the skis is above the gate. This does not mean that there is not considerable pressure on the skis at the gate; just that it is diminished. It is hard to see, but look at the bend of the skis in the third frame from the end (at the gate) - there is still pressure there. But, the last two frames have the skis much straighter - the pressure is very much reduced. Rainer is going almost straight in the last three frames - his turn is over - his is gaining speed. This is what I mean by a 'comma' shaped turn.

I will agree with BigE about tdk6's whirling rope.

tdk6's video form Massey University in New Zealand is very interesting. Take a look at the same skiing sequence showing the X-Y-Z views of the skier, and most telling, the video.



The person used for this demonstration appears to me to be a competent 'club racer' skier. It's only possible to see the last couple of turns, but he is completing his turns below the gate. This type of turn will have the major pressure on the skis at, or below the apex. It's not fair to compare this to a WC level racer.

TDK6's quote "There is hardly any pressure in the top part and increasing towards apex and then depending on how far across you need to finish your turn the pressure starts to decrease after apex." is correct for a competent skier, but in my opinion does not apply to WC skiers.

I think that most of us should start our turns earlier than we do - most of us are late. As PJ (Jones) says: "You can never start your turn early enough". We should try to get closer to what these WC guys and girls do.

Now perhaps we should get back to the four or five core concepts of skiing.
post #43 of 57
Quote:
Originally Posted by simplyfast View Post
No I think it is just fine to venture into a different topic. It is all related in a way. I see all these different posts and looks there is really progress in all. Hey how about my idea with the rubber band instead of the rope. And instead of "bringing the end of the circle to the ground, why not at 9:00 or 3:00 O' Clock? I think then the experiment does come really close to the skier. Also the shape of the turn/curve. Again watch your head if you really plan on doing that.

I also dare to suggest actually that the centrifugal force is biggest at the apex and right after that gravity will kick in and then combined those forces are at the highest. (A skier will fall also in that section of the turn, not in the upper portion).
Also a "tourist" will show you easily where the forces increase as he starts to skid out the rest of the turn.

Ski Instructors are many times the better examples, because they ski at moderate speeds. Zooming down an icy hill will cause even the most skilled skiers to make errors, that is why pointing at a WC Skier is many times not a good choice of demonstrating the techniques.

And it is the most ideal situation to turn at the apex, merely because it will allow you to ski the most possible and direct line and also it keeps the "angle of attack" as steep as possible. Turning high up on the gate or "late"makes you ski uphill to the next gate. At that point it may make more sense to switch to a Cross Country gear. Ok, just kidding.
Great information - I am not good at cross-country, and it's not so exciting for me. Lets keep going down with gravity.
post #44 of 57
Simplyfast . If you don't center the turn at the gate you've generally gone further/slower than you need to go. Exceptions exist, of course, such as rhythm changes, terrain changes, delay gates, etc. And really, it has little significance in freeskiing, where the apex is always the apex.
post #45 of 57
I did say that, did I not?

Quote:
Originally Posted by Rick View Post
Simplyfast . If you don't center the turn at the gate you've generally gone further/slower than you need to go. Exceptions exist, of course, such as rhythm changes, terrain changes, delay gates, etc. And really, it has little significance in freeskiing, where the apex is always the apex.
post #46 of 57
Quote:
Originally Posted by simplyfast View Post
I did say that, did I not?
Yep, you sure did,,, that's why I gave you the . The yellow thumb means RIGHT ON, I agree fully. My comments after the thumb were just me confirming and expanding on what you said, for the hoped benefit of the readers.
post #47 of 57
Thread Starter 
Quote:
Originally Posted by Rick View Post
Simplyfast . If you don't center the turn at the gate you've generally gone further/slower than you need to go. Exceptions exist, of course, such as rhythm changes, terrain changes, delay gates, etc. And really, it has little significance in freeskiing, where the apex is always the apex.
Is the center of the turn when skis hit apex?
post #48 of 57
The Center of the turn is the Apex. At least it should be.

Hey did you get your DVD already?

Quote:
Originally Posted by tdk6 View Post
Is the center of the turn when skis hit apex?
post #49 of 57
Oh, ok thanks. Sometimes I am not sure if what I write can also be read so that it makes sense.



Quote:
Originally Posted by Rick View Post
Yep, you sure did,,, that's why I gave you the . The yellow thumb means RIGHT ON, I agree fully. My comments after the thumb were just me confirming and expanding on what you said, for the hoped benefit of the readers.
post #50 of 57
So given that the apex is the tightest part of the turn, and is usually when you are pointing down the fall-line; where should the apex be relative th the gate in GS?????
post #51 of 57
Thread Starter 
In GS, how does "apex", "center of turn" and "rise line" relate to one annother?
post #52 of 57
Right next to the gate. 3 O'clock and/or 9 O'Clock.




Quote:
Originally Posted by GSS View Post
So given that the apex is the tightest part of the turn, and is usually when you are pointing down the fall-line; where should the apex be relative th the gate in GS?????
post #53 of 57
Thread Starter 
Quote:
Originally Posted by simplyfast View Post
Right next to the gate. 3 O'clock and/or 9 O'Clock.
What is apex on a course set at a slope with a side pich?
post #54 of 57
Don't know which pitch, just find the fall line.

Quote:
Originally Posted by tdk6 View Post
What is apex on a course set at a slope with a side pich?
post #55 of 57
Quote:
Originally Posted by Si View Post
A simple set of 2 fundamental core movements:

Release of the big toe ski edge (tipping to the little toe side) on the old outside ski.

Transfer of weight to the new outside ski.

IMHO these are best implemented at the fundamental level through a mechanism of old outside leg relaxation (retraction in the more extreme) and tipping towards the little toe side....
I'd add my 2 cents about these being the most fundamental movements. Most or all of the other movements enable or build on these basics of:
  1. relaxing or retracting the old stance leg, and
  2. tipping it to the new edge.

Of course there are a thousand other movements but if you can't do these 2 well, the rest won't do you much good. Good references for more info:
  • Ski the Whole Mountain by Eric and Rob Deslauriers
  • Anyone Can Be an Expert Skier I, II by Harald Harb
  • Breakthrough on the New Skis by Lito Tejada-Flores
post #56 of 57
Quote:
Originally Posted by GSS View Post
I think that most of us should start our turns earlier than we do - most of us are late. As PJ (Jones) says: "You can never start your turn early enough". We should try to get closer to what these WC guys and girls do.
What's great about skiing these days is that shaped skis give normal skiers to turn early and make great carved turns... without going supersonic speeds or having WC skills!
post #57 of 57
Connect the starting and finishing points of a turn with a straight line. The apex will be the point along the turn track furthest from that line. Generally the fastest line will be one that places the apex right at the gate,,, not above or below it. The falline does not have to correspond with the apex, but it often does.

Place the apex above or below the gate, and the max distance you've traveled from the straight line will be larger than if apex is placed at the gate. Above is called skiing a high line. It's safe, but it's not the fastest.

TDK6, the rise line is an imaginary line running uphill from the turning pole of a gate. it relates to apex only in the sense of acting as a reference point for initiating the turn. I say reference point because a fallacy exists that turns should be initiated at the rise line. Not the case in most arc to arc turns. If you haven't gotten on your edge and started the arc by the rise line you're in trouble.

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