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# Cross-over vs Cross-under

This was raised in the icono... thread, but since that is already a trainwreck I thought I create a new thread about it.

Quote:

Cross over, Cross under, is there really a difference. Anyone up to a fight(debate) ha ha about it.

I have never liked the term and I never use them, but a lot of people do.

I don't know what the formal definition is but perhaps:

Cross-under: Skis cross under a stable upper body in transition

Cross-over: Upper body cross over the skis

In both cases the CoM and skis cross paths.

Is there a difference, and what is it?

I'll let others give their view before I give mine.

While I'm sure the body crossing over skis versus skis crossing under the body may help some distinguish two different turns, that definition does nothing for me.  The actual motion is the same no matter the frame of reference, and the sun revolving around the Earth versus the Earth revolving around the Sun only changes the math.

I do have a distinction in my mind between the two turn transitions, and it has to do with momentum.  My CM is on a path down the hill.  If I alter that path by adding vertical acceleration in an upward direction so that the cross occur at a higher point, with my CM rising  versus it's previous path, I think of it as cross over.  If I cross with my CM lower than on it's previous path I think of that as cross under.  To achieve the cross under I typically  use more leg flexion to initiate (mostly, but not exclusively sudden active inside leg flexion).   More assistance from old inside leg extension to help achieve cross-over.  I originally only used cross-under in SL turns, but have learned to really enjoy rapid cross under at speed with Long radius skis - very exciting.

I will mention in passing, that the path to separate upper body and ski paths  seems easier to find for most folk when they are learning cross-under turns.

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Originally Posted by Ghost

I will mention in passing, that the path to separate upper body and ski paths  seems easier to find for most folk when they are learning cross-under turns.

Very good post. Cross nuder and cross over is distinguished by the way the body moves in the verticle plane. Cross under very little verticle movement with the legs doing the flexion extension required for edge change. Whereas in cross over the body moves verticle to allow movement of the legs laterallly.

Two ways to achieve the same thing.

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Originally Posted by shoal007

Very good post. Cross nuder and cross over is distinguished by the way the body moves in the verticle plane.

I know.  I'm 5.

So when would you use one vs. the other?

Should cross under be thought of as retraction turns? Does it lead to a quicker change in direction and edge engagement than cross over (where it seems you would extend - float - and then pressure edges)?

We have beaten this topic with a stick before.

Most people equate retraction turns with cross under. But most turns have some blend of cross over and under. For a single turn, cross under is not necessarily faster than cross over, but it is faster for multiple turns. You'll see top mogul skiers using retraction turns almost exclusively. Mix, match, lather, rinse, repeat.

Crossover (vaulting) occurs as a function of the CM trying to go straight and the edge platform acts much like the end of the pole vaulters pole. Crossunder works much the same except we absorb some of that vaulting. The virtual bump concept also is related to all of this and it's worth searching the archives for more information about appropriate applications of vaulting and absorbing through transitions. Just remember, intent dictates technique and deciding what outcome you wish to create will tell you which move is most appropriate.

Good point JASP,

For example, if your intent is to carve fast, high edge angle, edge-locked turns it is not possible to do cross over, because without absorbing the vaulting effect would send you sky high,  just like a pole vaulter.

If your intent is to ski slow, smeared turns a cross-under does not make sense because you don't have anything to absorb. You could still flex through the release/transition and keep the COM level, but IMO that kind of misses the point in why a retraction release is useful, and it kind of looks silly.

Then you have everything in between...

Quote:
Originally Posted by Jamt

Good point JASP,

For example, if your intent is to carve fast, high edge angle, edge-locked turns it is not possible to do cross over, because without absorbing the vaulting effect would send you sky high,  just like a pole vaulter.

If your intent is to ski slow, smeared turns a cross-under does not make sense because you don't have anything to absorb. You could still flex through the release/transition and keep the COM level, but IMO that kind of misses the point in why a retraction release is useful, and it kind of looks silly.

Then you have everything in between...

That makes a lot of sense to me JAMT...great way to think about it  as far as a sl radius is concerned, it seems that at times, one really has to be mindful ....if Marcel, in the previous thread's montage, hadn't been prepared and retracted when he did, well.....   we've all seen a racer upside down in the air.  But of course it's definitley a necessary move.  I think I now understand the gist of your post regarding this in turn mechanics 101, BTW

P.s. HAPPY THANKSGIVING, EVERYONE!!!!

Edited by zentune - 11/22/12 at 7:20am

Uh, Jamt, It's hard to speak in absolutes when it comes to transitions.

Svindal uses a cross over transition quite effectively in this montage. Yes his ski comes off the snow (as a result of vaulting) but instead of flexing, he is extending. Why? To gain maximum RoM prior to landing. When he lands he has already established a great stance for what he wants to do with the next turn. Could he have done the same thing flexing through the transition? It's hard to say for sure but what he did worked very well.

JASP, this is exactly why I don´t like the terms cross-over and cross-under. In this montage the CoM is more or less in free fall from somewhere between frame 3 and 4 until somewhere between 6 and 7, while the feet move under the CoM, so per som definitions of over/under this would be a cross under.

You can also be pretty certain that just before frame 4 the turn is released by a quick relaxation, but since the CoM is already in an upward trajectory the legs will lengthen after that.

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Originally Posted by justanotherskipro

Uh, Jamt, It's hard to speak in absolutes when it comes to transitions.

Svindal uses a cross over transition quite effectively in this montage. Yes his ski comes off the snow (as a result of vaulting) but instead of flexing, he is extending. Why? To gain maximum RoM prior to landing. When he lands he has already established a great stance for what he wants to do with the next turn. Could he have done the same thing flexing through the transition? It's hard to say for sure but what he did worked very well.

Note the bold text....of course he could of.  HH skis like that all the time.

Cross over and cross under are different movements of the body and are very easy to understand.  Above is unquestionably a cross over.  The obvious clue is how many fulcrum (not Jobert's fulcrums) points there are. In this case the feet roll over from one side to the other and so does the hip.  (note what is looks like in frame 4 starting at the top of the pic and later at frame 7).  Both the hip and the feet have changed sides in those 3-4 frames.

Cross under is different.  The hip is part of the upper body and really doesn't change sides at all.  The feet move out from under the body (or are already there) and then cross under the body headed toward the other side.  Therefore only one fulcrum point at the feet HIP.  It is a totally different body movement than the picture above.

In general whether you flex and extend or flex and absorb,  a crossover is possible and is generally used in medium to long radius turns.  Cross under, is more natural in short radius turns, bumps being the best example.

Don't believe it ?  Hop into a bump field of moderate to large bumps and try crossing over.

Edited by Uncle Louie - 11/23/12 at 1:46pm

So what is your definition of cross-over and cross-under then UL? My problem with these terms is that it seems most people have some idea in their head what it is, but unless everyone has the same idea, it is kind of useless.

We can't extend if we don't flex but the tail is still carving in frame four so I question if the CoM is in freefall prior to that frame. The big change is his right hand moves laterally. That along with the feet swooping back under the body are the likely reason for his core rising. Here's another montage where flexing is much more prevelent.

The idea here is that cross under typically involves flexing to a greater degree. The distance from the feet to the glute changes a lot more than during a cross over transition.

great discussion...very interesting!! so would it be appropriate to say that, among other things, that a cross over would produce more of an across the fall line effect (greater offset), whereas a crossunder would be more of a direct fall line move (less offset)? sorry still on a phone here....
No, it is so much simpler than that. It's about lateral displacement. Metronome like movements verse pendulum like movements.
Quote:
Originally Posted by Jamt

So what is your definition of cross-over and cross-under then UL? My problem with these terms is that it seems most people have some idea in their head what it is, but unless everyone has the same idea, it is kind of useless.

I did a little editing on my last post to clean it up a bit.

Quote:
Originally Posted by Uncle Louie
Cross over ...........  the feet roll over from one side to the other and so does the hip.   Both the hip and the feet have change(d) sides............

Cross under ................ The feet move out from under the body (or are already there) and then cross under the body headed toward the other side.  Therefore only one fulcrum point at the hip.

So, the definitions would be:
Cross over, the body crosses over the skis
Cross under, the skis cross under the body.

I caught a typo in my last post too.  I changed it here and typed through in my last post leaving the original error.  The HIP is the only fulcrum point in a cross under turn (not the feet)

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Originally Posted by justanotherskipro

The idea here is that cross under typically involves flexing to a greater degree. The distance from the feet to the glute changes a lot more than during a cross over transition.

Quote:
Originally Posted by justanotherskipro

No, it is so much simpler than that. It's about lateral displacement. Metronome like movements verse pendulum like movements.

That's pretty much it.

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Originally Posted by zentune

great discussion...very interesting!! so would it be appropriate to say that, among other things, that a cross over would produce more of an across the fall line effect (greater offset), whereas a crossunder would be more of a direct fall line move (less offset)? sorry still on a phone here....

A more across the fall line effect (given you have significant speed) would produce a more cross over type turn.

so...pendulum=crossover--more lateral distance (further) across the fall line, metronome=crossunder less distance across? just trying to get the nomenclature right...
Quote:
Originally Posted by justanotherskipro

No, it is so much simpler than that. It's about lateral displacement. Metronome like movements verse pendulum like movements.

If you are unweighted the pendulum is around the CoM per definition. So then a metronome like movement would imply you are not unweighted, and consequently the Svindal pictures would be cross-under.

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Originally Posted by Uncle Louie

Cross over, the body crosses over the skis
Cross under, the skis cross under the body.

Well, if a the body travels on a line that crosses the line of the skis the body crosses over the skis and the skis cross under the body, so that kind of verifies tek head original question whether there really is a difference.

Sorry but these definitions doesn´t do it for me.

I think the difference is more related to whether the transition is weighted or not, but then we have the problem with the WC GS type of transition that look kind of like a much slower transition where the legs are extended, but in reality the transition is unweighted and the legs are extended just to maintain snow contact.

What would you call the transition that Ligety showed in the Sölden training video, where he is way above the surface and extended?

I am familiar with UL's definitions as what I most commonly hear.

As Jamt points out though, the paths cross, so one going under or one going over seems to be more a matter perspective or frame of reference. If you put an ant on your ski boot it will see the com cross back and forth above it. While another ant located up near your com will see the feet cross under back and forth below it. They are both right.

Unweighting? I dunno.

I think the sensations trying to be described are relating to the extent the com and bos are decoupled during the transition. Not sure that exactly relates to unweighting, com rise, etc but I suspect a bunch of pieces of the puzzle work together.

 To be clearer, the crossunder sensation would be on the end of the spectrum being most decoupled between the bos and com.
Quote:
Originally Posted by Uncle Louie

A more across the fall line effect (given you have significant speed) would produce a more cross over type turn.

Makes sense...but as a racer, you at least some of the time (ie, if your looking ahead a few gates and have inspected adequately ) know what will be required to make a certain gate(s).  In that case, it would seem that there IS a capacity to anticipate a cross over vs. cross under move. So you say to yourself "here it comes...big offset...time for a cross over" (not that you have the time to actually say it, but you get my drift). I'm just implying that some times you are ready and are proactive and some times you get suprised...

P.s. it's not always something that just happens to you...it's also a move that you also actively make

Quote:
Originally Posted by justanotherskipro

No, it is so much simpler than that. It's about lateral displacement. Metronome like movements verse pendulum like movements.
Ah, finally something familiar to a recreational skier hidden in all the talk about Svindal and Hirscher (both of whom are delights to see). Thanks, jasp. Nobody I've talked with has seemed to have any idea what I've meant when I say my feet feel like pendulums. I thought I must be doing something wrong, but it sounds like maybe crossunder. All I know is it's much less effort and feels loverly. I credit the new boots if I'm doing something right, because I'm certainly not a better skier than I was last season.
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Originally Posted by cgeib

I am familiar with UL's definitions as what I most commonly hear.
As Jamt points out though, the paths cross, so one going under or one going over seems to be more a matter perspective or frame of reference. If you put an ant on your ski boot it will see the com cross back and forth above it. While another ant located up near your com will see the feet cross under back and forth below it. They are both right.
Unweighting? I dunno.
I think the sensations trying to be described are relating to the extent the com and bos are decoupled during the transition. Not sure that exactly relates to unweighting, com rise, etc but I suspect a bunch of pieces of the puzzle work together.
 To be clearer, the crossunder sensation would be on the end of the spectrum being most decoupled between the bos and com.

I must admit, unweighting "crossed" my mind...but I know that the way of looking at/describing these things have evolved...good stuff!!!

The ant analogy is cool...2 points of view observing the same thing.

Edited by zentune - 11/23/12 at 9:41pm
Quote:
Originally Posted by cgeib

Unweighting? I dunno.
I think the sensations trying to be described are relating to the extent the com and bos are decoupled during the transition. Not sure that exactly relates to unweighting, com rise, etc but I suspect a bunch of pieces of the puzzle work together.
 To be clearer, the crossunder sensation would be on the end of the spectrum being most decoupled between the bos and com.

Ok, but then we would need to define what decoupled bos and com is. If it means that the bos is not affecting the com, isn´t that the same thing as beeing unweighted?

My only conclusion is still that I will continue to not use the terms.

Quote:
Originally Posted by Uncle Louie

A more across the fall line effect (given you have significant speed) would produce a more cross over type turn.

Not to beat a dead horse here, but to further clarify/add to my earlier response to this, I would say that with an "across the fall line effect" one would probably want to employ what I now understand as a cross over...but it is not (to my mind at least) "produced" automatically, on it's own...as if by virtue of the situation itself.  One still has to be aware, and in proper position. I think of the good skier as both the pilot, AND the passenger... at the same time, perhaps...Just a thought.

I tend to agree, Jamt, the terms don't seem to lend clarity.

I was playing with this a little on my run down after skinning this morning. I guess I feel what I understand to be crossunder to be more along the lines of different trajectories and maybe more a decoupling of the lateral connection/component.

I suppose I understand the desire to relate this to unweighting and maybe it technically is. Though, I think of unweighting more concerning the connection between the bos and the snow, and the vertical piece. I might be more inclined to think of this as float vs unweighting, but that is just my distinction and likely doesn't lend clarity either, but seems more fitting for a more dynamic turn where things have ramped up to the catch and toss mode where we can work off the impulse from the ski to define our trajectory and not just in opposition to or management of gravity.

To clarify I might suggest that a crossunder be a decoupling between the bos and com while maintaining the connection and interaction between the ski and the snow. So since the skis are still engaged and working when the resistance of the com is removed they seemingly fire across underneath and this gives rise to the feeling of the feet/skis crossing under.

Is it necessary to "unweight" here? I don't think so. I think we could do "retraction" turns attempting to keep our com stable with skis arcing back and forth in an attempt to maintain constant pressure under foot throughout the turns and feel this "crossunder". Likewise, I think we can ramp it up to dynamic turns reaching across the hill with a float of the com and still keep the skis interaction working to the extent necessary to get the skis to zing across.

Whatever, have fun experimenting with it

I think it's worth repeating, it's much simpler than that! Don't, and I repeat don't add more to it that that. That's where the confusion starts.

Here's a simple way to experience the two.

Stand in a door way, flex one leg and let yourself fall towards one side of the doorway. Since there is no momentum from a ski turn we need to extend that bent leg to return to upright. If we then flex the other leg we fall to the other side. If we do this in a linked way the body is tipping over the feet that don't move. That is crossover in it's purest form. If you could hang by the top of the doorway and swing your feet laterally back and forth, that's cross under in it's purest form. Neither happen exclusively as we ski but you get the point.

So how does this relate to the real world? CoM's not being a fixed point it's hard to talk about the hips as the exclusive place where the CoM resides. So projecting the path of the CoM cannot be offered that way either. Throw the feet out to the side, or bend sideways at the waist and it moves laterally outside the body. Even moving an arm (9% of our body mass) away from our body shifts the CoM. It's something Svidal did in that montage, he moved the CoM out enough for his entire body to begin moving (untipping) towards a more upright stance. In Vonn's case she lets the feet swing around under her body and her head is much closer to the pivot point than her CoM or hips. So it's not always about the CoM being the pivot point any more than the CoM always being a fixed point in the body. As Bob often says it's about the movements and IMO communicating how to make those moves is more difficult when we get too left brained about those moves.

As far as trajectories down, or across the hill, those line choices are completely variable and depends on where you want to go. That goes for the core and the feet, as well as the entire body.

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