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Deb Armstrong: Use of the inside leg to change turn radius

François Pugh

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This does not synch with my experience. If I choose to lift the ski off the snow as i raise the inside knee, it comes up. If I choose to keep the ski on the snow as I raise that knee towards my inside armpit, the ski stays on the snow.

I don't consider stance width as an independent variable with respect to whether the inside ski is airborne or not.

However, when I want my inside foot to be near my outside knee at the fall line, I move it closer as the knee comes up towards the armpit (and no, it never gets there).


I'm not sure stance width is a determinant - for me. But since intent is working, and not proprioception of stance width, I'm just not sure. Maybe stance width is an unacknowledged factor.

I look forward to hearing what others have experienced.
It doesn't work alone; you have to have your balance in the right place. You have to counter balance as needed to do more than just lift the ski off the snow.
 

Mike B

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A subtlety that my Taos ski week instructor helped me understand (even though he was not specifically addressing the knee):

If you have a narrow stance and raise the inside knee, that ski just comes off the snow.
If you have a somewhat wider stance and some weight on the inside ski, raising the inside knee drops the chest towards it and gives you bigger angles.
I came to this same conclusion playing with widening my carving stance but not changing my turn intent.
Excellent description.
Edit: Wilson in the first video mentions letting the natural lead work for him. Thats how it feels. It doesnt feel like you are holding any body parts back (especially the inside ski).
 
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Mike B

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Language is a funny thing. To me "drive the knee" means deliberately make it go where you want it to be. Focusing on inside knee position can often lead to a breakthrough when searching for easier access to higher edge angles (due to removal of blocking proper hip alignment). You also have to know where it should be to achieve your goals.
Yep, I always think of Bob Barnes and his "go there" mantra. Pulling the inside foot back may work to achieve some goals, but its more like driving in reverse...at least to me when it comes to this topic.
 

Mike B

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No doubt. That was much better and it's good to see that she took the criticism of the previous video to heart and felt it was worth providing some clarification. The only think I wish she would have added to that explanation was the foot pullback along with her mentioning the dorsiflexion to close the ankle. She was showing the heel pulled to the a$$ somewhat, but did not stress it. We do not want to introduce a bunch of tip lead that leads to ski "shuffling" as you move from turn to turn, but I like her emphasis on the retraction of the inside leg in the turn (even though she never calls it retraction). My opinion on this movement pattern is that it's more important to teach this as a retraction of the inside leg with a focus on bringing the heel rearward and upward to your butt, rather than "driving the knee forward". I think for most skiers, their "lizard land brain" isn't going to get the right inputs by using a 'knee drive" focus. Once again, the knee's movement "forward" is an outcome resulting from retraction of the leg as the input (a leg hamstring curl). It's not by shoving the knee forward.
That's acceptable. Perhaps for the folks who have mastered pulling the inside foot back adding the knee drive could really help. For those that can drive the knee but produce lots of unnatural lead, holding the foot back with dorsi flexion is the answer.
 

geepers

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This does not synch with my experience. If I choose to lift the ski off the snow as i raise the inside knee, it comes up. If I choose to keep the ski on the snow as I raise that knee towards my inside armpit, the ski stays on the snow.

I don't consider stance width as an independent variable with respect to whether the inside ski is airborne or not.

However, when I want my inside foot to be near my outside knee at the fall line, I move it closer as the knee comes up towards the armpit (and no, it never gets there).


I'm not sure stance width is a determinant - for me. But since intent is working, and not proprioception of stance width, I'm just not sure. Maybe stance width is an unacknowledged factor.

I look forward to hearing what others have experienced.

Agree that it's not so much stance width as where the CoM is relative to the GRF vector.

On the lateral plane if the CoM is below the GRF vector then we will laterally biased to the inside of the turn and will continue to move inside until something changes. Such as the inside leg not getting out of the way (unloading the outside ski) or the CoM moving above the GRF vector through angulation. When the CoM is above the GRF vector then we are laterally balanced to the outside of the turn and will move laterally out of the turn.

There's a little complicating factor in the pace at which the CoM/skis cross.

If done slowly with a tendency to re-center at transition before committing to the new turn then the biasing to the new turn has to be deliberate. Withdrawing the support of the new inside leg from a balanced position is certainly one way. (But if we are laterally balanced over the new outside ski, lifting the new inside leg will do little but take the ski off the snow.)

If done at a faster pace with no pause (some may call it toppling) then the CoM will already be moving inside the new turn. If we're laterally balanced to the inside then the CoM will accelerate inside. If we're laterally balanced to the outside then the movement inside will begin to slow down and eventually reverse. Which we are going to have to do to get out of that turn for the next. Rinse, repeat.


Biased to the inside.
Toppling1.JPG


Biased to the outside.
Toppling2.JPG
 

JESinstr

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Yep, I always think of Bob Barnes and his "go there" mantra. Pulling the inside foot back may work to achieve some goals, but its more like driving in reverse...at least to me when it comes to this topic.
It is important to remember that it is the ski that takes you "there" so first and foremost, one must be in alignment with the ski. Pulling the inside foot back is a remedy for some.
 

JESinstr

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Agree that it's not so much stance width as where the CoM is relative to the GRF vector.

On the lateral plane if the CoM is below the GRF vector then we will laterally biased to the inside of the turn and will continue to move inside until something changes. Such as the inside leg not getting out of the way (unloading the outside ski) or the CoM moving above the GRF vector through angulation. When the CoM is above the GRF vector then we are laterally balanced to the outside of the turn and will move laterally out of the turn.

There's a little complicating factor in the pace at which the CoM/skis cross.

If done slowly with a tendency to re-center at transition before committing to the new turn then the biasing to the new turn has to be deliberate. Withdrawing the support of the new inside leg from a balanced position is certainly one way. (But if we are laterally balanced over the new outside ski, lifting the new inside leg will do little but take the ski off the snow.)

If done at a faster pace with no pause (some may call it toppling) then the CoM will already be moving inside the new turn. If we're laterally balanced to the inside then the CoM will accelerate inside. If we're laterally balanced to the outside then the movement inside will begin to slow down and eventually reverse. Which we are going to have to do to get out of that turn for the next. Rinse, repeat.


Biased to the inside.
View attachment 157966

Biased to the outside.
View attachment 157967
Excellent analysis.
But pace of transition it is a lot more than a little complicating! It needs to be a change in mindset. From the teaching perspective it is a critical consideration regarding the methodologies we use. This is the conundrum in moving out of the low velocity beginner phase.

Since low velocity does not support inclination, the process of turn initiation reverses from angulation to inclination as velocity increases. IMO
 

markojp

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A subtlety that my Taos ski week instructor helped me understand (even though he was not specifically addressing the knee):

If you have a narrow stance and raise the inside knee, that ski just comes off the snow.
If you have a somewhat wider stance and some weight on the inside ski, raising the inside knee drops the chest towards it and gives you bigger angles.

But folding at the waist does nothing to shorten the leg... it only feels like you have. The trick is the mechanism for shortening the leg without excessive tip lead or folding at the waist. I think it was Tom G who said imagine lowering your inside butt cheek to your heel. This sounds completely wrong, but works incredibly well so long as you’re conscious of 'down' to the heel vs. 'inside' i.e., dumping.
 

Andy Mink

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Well, this has been quite the Tuesday morning rabbit hole! Lots of good stuff. For what it's worth, and it's probably been said here in several different ways, I find thinking about keeping my hips as level as possible, like the "carry the tray" thing with your hands, to help. I saw a video of MS explaining that and it resonated. If I can remember to do that along with the 500 other things that go into a turn, things work out pretty well. Think Infinity Move. Reach down the hill with the pole to initiate a turn and ski around that point. Etc.
 

Sledhead

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Geepers, I really like your graphic. Did you make it yourself? I agree with everything except for the use of the term “bias” when I am fairly confident that the differences in these two photos are about timing, something not mentioned in your explanation. Since the term “bias” indicates some sort of tendency only a portion of skiers will experience, I am not sure how that works in this situation. I am fairly confident that the first photo was taken during turn phase one and the second is turn phase three. Other than for the obvious difference in the photographer's vantage point, each photo could easily be from the same turn. Typical timing: TP1 - inclination and extension. TP3 - angulation and flexion.

I think that the better term may be “leading” as in we are leading our CoM ahead of where the ground force vector is at any given moment of time. Leading too far ahead can be as detrimental as the more typical example of following too far behind. Because the goal is actually being completely lined up between the CoM and GRV, because the GFV is always moving, the only way to remain lined up is through leading or constant movement in that direction. It is like Brady leading Gronk on his path into the endzone.

If you were to draw both lines, the ground force vector and the line of gravity between the CoM and BoS, and measure the angle between the two, the smaller the better. And, of course, ahead rather than behind is better as well.
 

James

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Agree that it's not so much stance width as where the CoM is relative to the GRF vector.

On the lateral plane if the CoM is below the GRF vector then we will laterally biased to the inside of the turn and will continue to move inside until something changes. Such as the inside leg not getting out of the way (unloading the outside ski) or the CoM moving above the GRF vector through angulation. When the CoM is above the GRF vector then we are laterally balanced to the outside of the turn and will move laterally out of the turn.

There's a little complicating factor in the pace at which the CoM/skis cross.

If done slowly with a tendency to re-center at transition before committing to the new turn then the biasing to the new turn has to be deliberate. Withdrawing the support of the new inside leg from a balanced position is certainly one way. (But if we are laterally balanced over the new outside ski, lifting the new inside leg will do little but take the ski off the snow.)

If done at a faster pace with no pause (some may call it toppling) then the CoM will already be moving inside the new turn. If we're laterally balanced to the inside then the CoM will accelerate inside. If we're laterally balanced to the outside then the movement inside will begin to slow down and eventually reverse. Which we are going to have to do to get out of that turn for the next. Rinse, repeat.


Biased to the inside.
View attachment 157966

Biased to the outside.
View attachment 157967
Not buying it in those photos. You don’t know the speed. He could easily be nearly totally weighted on outside ski in top photo.
29DCFBFB-440C-4222-9A49-5D3C5794B982.jpeg

0F920DC1-54CE-4652-8454-6DA2063709EA.jpeg
 

JESinstr

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Well, this has been quite the Tuesday morning rabbit hole! Lots of good stuff. For what it's worth, and it's probably been said here in several different ways, I find thinking about keeping my hips as level as possible, like the "carry the tray" thing with your hands, to help. I saw a video of MS explaining that and it resonated. If I can remember to do that along with the 500 other things that go into a turn, things work out pretty well. Think Infinity Move. Reach down the hill with the pole to initiate a turn and ski around that point. Etc.
A drill I use to keep the pelvis level is to take your poles and hold them horizontally with palms down and hands shoulder width apart. Then, cross your hands and tuck the poles up under the arm pits. Ski with the goal of keeping the poles perpendicular to gravity while at the same time building edge angles by shortening the inside leg and moving the pelvis inside the turn while endeavoring to keep the upper body (Jacket Zipper) vertical to gravity.

IMO this is good thread because it deals with the fundamentals of advanced skiing.
 

geepers

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Geepers, I really like your graphic. Did you make it yourself? I agree with everything except for the use of the term “bias” when I am fairly confident that the differences in these two photos are about timing, something not mentioned in your explanation. Since the term “bias” indicates some sort of tendency only a portion of skiers will experience, I am not sure how that works in this situation. I am fairly confident that the first photo was taken during turn phase one and the second is turn phase three. Other than for the obvious difference in the photographer's vantage point, each photo could easily be from the same turn. Typical timing: TP1 - inclination and extension. TP3 - angulation and flexion.

I think that the better term may be “leading” as in we are leading our CoM ahead of where the ground force vector is at any given moment of time. Leading too far ahead can be as detrimental as the more typical example of following too far behind. Because the goal is actually being completely lined up between the CoM and GRV, because the GFV is always moving, the only way to remain lined up is through leading or constant movement in that direction. It is like Brady leading Gronk on his path into the endzone.

If you were to draw both lines, the ground force vector and the line of gravity between the CoM and BoS, and measure the angle between the two, the smaller the better. And, of course, ahead rather than behind is better as well.

Bias is used in the CSIA latest "Physics of Skiing" manual.

1643742043595.png


Those graphic are snapshots from a short CSIA vid that goes with that manual. And, yep, the actual CoM/GRF positioning doesn't need to be large to result in moving inside/outside.

I'm not sure I agree that the goal is "actually being completely lined up between the CoM and GRV". Sure, we want to be very close in alignment as it helps manage forces, however we want to flow in and out of the turns. Some-one once told me "always be moving in or moving out" and that requires an amount of imbalance.




Not buying it in those photos. You don’t know the speed. He could easily be nearly totally weighted on outside ski in top photo.

It's in a vid so there's a good idea of the skier's speed. MHO both would have been better drawn at slightly earlier positions in the turn when the toppling in/out was in full swing. But they make the point.
 

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