What's the Purpose of Separation in a Ski Turn?

[Mike King]

So, the other thread has kind of gone off track, so let's start a new thread and see where this goes. What do you think the purpose is of rotational separation in a ski turn? Is there a difference in rotational separation between phases of the turn? Is there a difference between short, medium, and long turns? What are the biomechanics and physics that dictate the parameters for rotational separation?

 

[Dakine]

Back in the old days folks used the term "Split Rotation" to describe the movement pattern where the lower body was rotating one way while the upper was rotating the other.
In the days of Stein's Reverse Shoulder Technique this got a lot of emphasis.
I still think it is a useful concept but many now hate on the whole concept of rotation.

 

[4ster]

Back in the old days folks used the term "Split Rotation" to describe the movement pattern where the lower body

I think you are describing counter rotation. My understanding of Split Rotation is where you would begin the turn with counter rotation & finish with rotation or vice-versa.

Separation describes independence between the upper & lower body.

 

[David]

I think you are describing counter rotation. My understanding of Split Rotation is where you would begin the turn with counter rotation & finish with rotation or vice-versa.

Separation describes independence between the upper & lower body.

Sounds like the old reverse shoulder style.

I think lower body rotation with a stable upper body is more important with short quick turns & bumps than in longer rounder turns and is something I'm always conscious of. But I'm just a hack trying not to kill himself in front of others...

 

[François Pugh]

From an unstructured, unorthodox, untrained view point:

A key to good skiing is separate flight paths for skis (which are the base of support) and centre of mass (which accelerates due to applied forces) . Upper and lower body separation greatly increases ones ability and freedom with respect to available flight paths.

When the upper body is not forced to be pointing or to rotate the same as the lower body, you can do much more. You can angulate better by increasing the range of motion you have in a given direction. You can build up muscular tension to be used to rotate one part or another of the total free-body being acted upon by forces (e.g. skis). You can build up rotational inertia, which can be used later.

It frees up your skis and your body (in terms of what they can do); it's like having a dog on a leash instead of a pole; the dog can go whereever he wants within the reach of the leash (only you control where the dog decides to go as well).

Of course with freedom comes responsibility, and it helps if you know what to do with that freedom. That's why ski instructors have specific instructions on how to move different parts of you body, and talk about angulation and counter (position or movement) rotation. I'll leave the specifics to them, and remain a free-thinker.

I will state, however, that the greater range of motion, in my experience, includes a greater range of separation - more counter in tighter turns.

 

[David Chaus]

It’s not simply rotational separation, it’s separation at the hip sockets, both rotation and opening/closing of the joint.

As @François Pugh posted above (just beat me to it), the purpose of the separation is to allow the relationship between the COM and BOS to change throughout the phases of a turn and in transition from left turn to right turn, and to maintain balance in the process so that the COM is stacked above the BOS in relation to the predominant and changing forces acting on the whole system.

And that may be the longest single sentence I’ve ever posted here.

That said I suspect most people here already know all this.

 

[Dakine]

One thing is that women are built differently than men with more mass in the lower body.
Many women have a hard time getting rotational separation because of this.
Obviously body type is important too but as a gross overgeneralization this is my experience.

 

[martyg]

It depends on intent. Is it different for different turn radi? Yes. Your COM goes where you want to go. Anything other than that and you have a huge agreement error, which robs efficiency.

 

[Mike King]

A key to good skiing is separate flight paths for skis (which are the base of support) and centre of mass (which accelerates due to applied forces) . Upper and lower body separation greatly increases ones ability and freedom with respect to available flight paths.

It isn't clear to me that rotational separation allows for greater ability and freedom in diverging paths between the upper and lower body. Why do you believe this to be so? And how does it manifest itself in the biomechanics of the body?

When the upper body is not forced to be pointing or to rotate the same as the lower body, you can do much more. You can angulate better by increasing the range of motion you have in a given direction. You can build up muscular tension to be used to rotate one part or another of the total free-body being acted upon by forces (e.g. skis). You can build up rotational inertia, which can be used later.

From a biomechanics point of view, there's a relationship between rotational separation and the amount of hip angulation you can access. With the hips square to the feet, you can access less hip angulation directly orthogonal (at a right angle to) the feet. With the pelvis angled to the legs, you can access more hip angulation to the rear, and less to the front.

What this means in a ski turn is that after the fall line (as the skis come back to you) you are blocked in angulation. So by rotationally separating after the fall line, you can increase the amount of hip angulation that you can access.

It’s not simply rotational separation, it’s separation at the hip sockets, both rotation and opening/closing of the joint.

As @François Pugh posted above (just beat me to it), the purpose of the separation is to allow the relationship between the COM and BOS to change throughout the phases of a turn and in transition from left turn to right turn, and to maintain balance in the process so that the COM is stacked above the BOS in relation to the predominant and changing forces acting on the whole system.

So how does rotational separation allow the relationship between the CoM and BoS to change? Are you suggesting it affects fore/aft balance? Foot to foot pressure?

 

[geepers]

Interesting question.

What's happening in these short and long turn examples? (Same skier.)

 

[Sanity]

Often at the beginning of the turn there's some steering. Counter rotation of the upper body is helpful for steering. Whether you intend to arc to arc carve or not, you always need to be prepared for steering which is probably the number one reason for counter. First of all, counter provides mass to lever against to rotate the lower portions without ending up in a bad position. For example, if you aren't countered and you have to steer, then you'll end up immediately in the back seat.

Counter also allows the body to angulate more easily since we fold to the front better than to the side, and it's this increased angulation which probably gives people a sense of better grip as well as keeping the center of mass from getting too far aft.

 

[Dakine]

Not to mention the need to keep the shoulders and even more the head looking downhill.
One of the best exercises I know for any level skier is to pick an object at the bottom of the run and keep looking at it as you turn.
The short turns above are a great example of this.
His head tracks like an owl's as his body turns.

 

[razie]

Counter also allows the body to angulate more easily since we fold to the front better than to the side, and it's this increased angulation which probably [...] keeping the center of mass from getting too far aft.

How? I think that if I just bend forward at the hips, my hips move back and my shoulders move forward and I remain balanced on the same point on the ski?

 

[François Pugh]

It isn't clear to me that rotational separation allows for greater ability and freedom in diverging paths between the upper and lower body. Why do you believe this to be so? And how does it manifest itself in the biomechanics of the body?



From a biomechanics point of view, there's a relationship between rotational separation and the amount of hip angulation you can access. With the hips square to the feet, you can access less hip angulation directly orthogonal (at a right angle to) the feet. With the pelvis angled to the legs, you can access more hip angulation to the rear, and less to the front.

What this means in a ski turn is that after the fall line (as the skis come back to you) you are blocked in angulation. So by rotationally separating after the fall line, you can increase the amount of hip angulation that you can access.



So how does rotational separation allow the relationship between the CoM and BoS to change? Are you suggesting it affects fore/aft balance? Foot to foot pressure?

Well, you've answered a big part of your own question. You can only get so much angulation by bending sideways, pinching your hips to your ribs at the side. Rotate your upper body and you can get some more by, as it were bending forwards to the side.
@razie . Yes the typical move of bending at the waist to get more forward typically results in a compensating butt backwards move, but it doesn't have to.
On a related note ski straight and move your head to the side, notice you naturally compensate to stay in balance by moving your hips to the other side, at least most folks do.

 

[razie]

.
On a related note ski straight and move your head to the side, notice you naturally compensate to stay in balance by moving your hips to the other side, at least most folks do.

Yup. That's a big point of angulation, to allow more inclination of the lower body and provide more grip, without changing really the COM/BOS relationship, which is dictated by physics of the turn...

But the point of hunching forward at the hips cannot be simply to move the hips back while staying in the same place...?

 

[François Pugh]

Yup. That's a big point of angulation, to allow more inclination of the lower body and provide more grip, without changing really the COM/BOS relationship, which is dictated by physics of the turn...

But the point of hunching forward at the hips cannot be simply to move the hips back while staying in the same place...?

It isn't. Look at your avatar. You would not have that much angulation without being counter rotated.

BTW, an advantage to being angulated instead of simply inclined with the same centre of mass location is the ability to adjust to sudden changes (e.g. if a ski suddenly slips out or hits something).

 

[Sanity]

How? I think that if I just bend forward at the hips, my hips move back and my shoulders move forward and I remain balanced on the same point on the ski?

Everyone skis with a forward leaning angle of their upper body. No one is completely straight up and down. If they are completely straight up and down then rotating the upper body wouldn't have much effect on the COM. But, if you are leaning forward and rotate your upper body counter to the turn, then the center of mass moves to the outside like it does when you do hip angulation. Imagine a stick straight into the ground normal to the surface. If you rotate the stick around an axis also normal to the surface, right at the center where the stick is in the ground (down the middle of the stick), then the center of mass is unchanged. Now lean the stick over some, rotate that stick around the same normal axis (which is no longer straight down the stick), and what you'll see is that the stick's center of mass changes relative to the contact point on the ground. So, if your upper body is leaning forward, and you're making a left turn, then if you rotate the upper body clockwise (looking down) the center of mass moves to the right (looking down the hill) which is more towards the skis. So, for a given edge angle the center of mass is now closer to the skis.

I wasn't sure if you're asking why counter provides a similarity to angulation or why lack of counter puts you in the back seat. So, above is why counter is like angulation. The reason you end up in the back seat without counter has to do with steering. It's more complicated. It has to do with where the upper body ends up relative to the skis after steering. With counter the upper body is already in the right place to begin the turn once steering is done, but without counter the upper body is in a great spot for the end of the last turn, but not the right spot for the beginning of the next turn. To begin a left turn, the upper body needs to be forward and inside, but if you steer without counter, the upper body will be back and to the outside relative to the skis, because the upper body will be mostly where it was at the end of the last turn or even slightly rotated more in the wrong direction. Inside and forward at the end of the last turn, is outside and back relative to the start of the next turn. Counter lets you get the upper body in the right place for the start of the next turn after steering. With arc to arc carving, it's a longer transition where you move your body diagonally forward, and counter isn't necessary to get into the right position at the start of the next turn.

 

[oldschoolskier]

Separation/isolation or whatever term you want to use is best for instructors/analyst. As to using it to instruct IMHO it is a bad thing for students.

Let me give an example, my son how has brain damage, when we taught him skills it was better to show the entire skill…..no seperation. If things got broken down and taught as individual tasks it patterned and he got stuck on one action, taught as a complete action(s) we could correct steps.

So…..separation is important to analysis yet use teach it separate we can cause issues that cause more harm.

Hopefully this makes sense and answer some questions and likely cause a few others.

 

[razie]

TW, an advantage to being angulated instead of simply inclined with the same centre of mass location is the ability to adjust to sudden changes (e.g. if a ski suddenly slips out or hits something).

Yes! That is benefit #1 of separation in any plane, imho: range of motion for dynamic balance!

As soon as you lock up body segments, square, rotation leaning in etc, you reduce the available ROM for balance in this or that plane/direction and the skiing suffers correspondingly.

 

[razie]

But, if you are leaning forward and rotate your upper body counter to the turn, then the center of mass moves to the outside like it does when you do hip angulation. Imagine a stick straight into the ground normal to the surface. If you rotate the stick around an axis also normal to the surface, right at the center where the stick is in the ground (down the middle of the stick), then the center of mass is unchanged. Now lean the stick over some, rotate that stick around the same normal axis (which is no longer straight down the stick), and what you'll see is that the stick's center of mass changes relative to the contact point on the ground. So, if your upper body is leaning forward, and you're making a left turn, then if you rotate the upper body clockwise (looking down) the center of mass moves to the right (looking down the hill) which is more towards the skis. So, for a given edge angle the center of mass is now closer to the skis.

It doesn't though, does it? As discussed: when bending forward at the waist, to stay in balance, the hips naturally move back. So when you turn, the hips simply move in too.

Remember, angulation does not move the average COM to the outside of the turn, it merely allows more inclination at the legs, i.e. more angles. If the average COM would move outside when you angulate, there would be no point in doing it, it would be a negative result, as you would simply wash out of the turn.

Similarly with your example, if counter would move more weight outside of the let's call it "original" COM - BOS axis, you wash out from the turn... that's not a benefit! Luckily, that is not what happens unless allowed on purpose at a certain point in the turn...

There are big benefits from bending forward at the waist some, but being more forward is not one of them. "Hunch forward more to be more forward" is not a thing, is it? How many here teach that?