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RACING A TRAIN THROUGH THE TRANSITION FROM ONE TURN TO THE NEXT

post #1 of 21
Thread Starter 

In another thread we were discussing balance and the dual paths (CoM and BoS) concept. It was suggested and agreed to by everyone that during a turn the feet must be moving faster than the body since they cover more ground in the same amount of time. I threw out the image of a car racing a train to an intersection. Thus the title of this thread. I'm hoping to discuss the outcome of these three different transitions through the lens of a race to the intersection (cross over point).
1. What happens when the feet win the race to the intersection and preceed the body into the new turn?
2. What happens when the body wins the race to the intersection and preceeds the feet into the new turn?
3. What happens when they arrive at that intersection at the same time?


 

post #2 of 21
Your right ..if you don't go faster then the terrain on the tracks it will take you out befor you get to the terrain station at the bottom of the hill!!
post #3 of 21
Quote:
Originally Posted by justanotherskipro View Post

1. What happens when the feet win the race to the intersection and preceed the body into the new turn?

A retraction, cross thorugh transition is used. Both knees are strongly flexed, and hips are aft of feet at edge angle neutral during the transition.  The skier either gets their new outside leg extended again by the apex of the new turn, into a strong position, or they go through the entire turn with hips aft because they neglect to extend the outside leg.   

2. What happens when the body wins the race to the intersection and preceeds the feet into the new turn?

A very full cross over transition, with the new outside knee extended enough and ankle flexed enough, to move the Center of Mass ahead of feet at edge angle neutral.  The new turn starts very aggressively with load on the shovel of the skis right at initiation.


3. What happens when they arrive at that intersection at the same time?

A cross over transition takes place, with the CM directly over the feet, and the new outside leg functionally extended at edge angle neutral.  Good ski to snow contact is generally maintained all the way through the transition, and the new turn can be initiated very smoothly, with the skier in an efficient state of centered fore/aft balance. 

post #4 of 21
Here, at the glossary on our website are a couple demos of the feet beating the body (cross through), and feet and body arriving at the same time (cross over).  Notice in cross through the new outside leg gets long and strong by apex.

http://www.yourskicoach.com/YourSkiCoach/C.html
post #5 of 21
If the skier does nothing to adjust the speed and/or fore aft postion of his skis, then the new turn will be started with weight too far fore or aft or with weight centered.

If the skier thinks to pull the skis back or otherwise adjust things, all bets are off.  Good skiers will adjust so as to apply pressure to the part of the ski that needs it without needing to think about it.  Just like a runner will lean back when he is slowing down quickly and lean forward when starting a race.
post #6 of 21
Rick, on your website you say about cross over: "It requires slightly more effort than cross through does to perform, because extending before edge angle neutral requires a battle with gravity."

It is true that the effort in turn exit is greater, but isn't effort in the extension into the new turn bigger in the cross through, thus evening things out?

Personally I always try go for the cross-through when carving, but it sometimes ends up with crossover when pressuring the inside too much or too long.
post #7 of 21
Quote:
Originally Posted by Rick View Post

Here, at the glossary on our website are a couple demos of the feet beating the body (cross through), and feet and body arriving at the same time (cross over).  Notice in cross through the new outside leg gets long and strong by apex.

http://www.yourskicoach.com/YourSkiCoach/C.html
 
Those two entries had no photos for me, was I missing something? Maybe it's the quicktime plugin not working?
I see you went to Les Deux Alpes last summer! Love that place. What fun with real snow and no salt!
post #8 of 21
 Tog, those two entries are actually revolving quicktime video clips.  My tech dept. tells me it could be you don't have the needed quicktime plug ins, or possibly have your plug ins turned off.  

Les Deux Alpes was super.  I now love it too.  What a beautiful corner of the world.  
post #9 of 21
This is fine as long as racing a train remains a mere metaphor.  Too many people die actually racing trains.  http://www.oli.org/
post #10 of 21
Thread Starter 
Do we really need a disclaimer here? How silly! The visual image comes from an old movie stunt not from any suggestion to literally race a train. It points out how out of context an idea can be taken when it's intepreted as more than it is.
post #11 of 21
Quote:
Originally Posted by Jamt View Post

Rick, on your website you say about cross over: "It requires slightly more effort than cross through does to perform, because extending before edge angle neutral requires a battle with gravity."

It is true that the effort in turn exit is greater, but isn't effort in the extension into the new turn bigger in the cross through, thus evening things out?

Personally I always try go for the cross-through when carving, but it sometimes ends up with crossover when pressuring the inside too much or too long.

Hi Jamt.  You make a good observation.  Whether it's cross over, or cross through, the extension does have to happen at some point.  In fact, when doing a pure version of cross through, the old inside (uphill) leg needs to be flexed beyond its state of flexion at the end of the turn.  That extra flexion also requires extra extension fo the new turn, so from a movement standpoint cross over is actually more efficient.  

From an energy consumption standpoint, the greater effort I spoke about in cross over has to do with the fact that some of the extension is vertical (the center of mass is lifted), where as in pure cross through the CM moves laterally as the extension happens.  No lifting, and no fighting gravity.  There are plenty of pros and cons for each alternative, but one of the cons of cross over is indeed that slight extra energy usage.  How much extra energy draw actually happens depends on how extensive the CM rise is.  it ranges from no extension of the old inside leg at all as you approach edge angle neutral, to full (functional) extension by edge angle neutral, and anywhere in between.  The video clip in the glossary on my website shows full extension.  

That said, there are benefits to cross over too.  I mention some in the glossary.  Once a skier understands the full picture, they just need to weigh  what's most important at the moment.  
post #12 of 21

Ok, thanks for the clarification. I guess the cross-through effort also depends on how deep you flex and how aggressive you extend. I have a feeling that in cross-over the extension cannot be too aggressive, becuase that will make you airborne in the transition.

From a physics point of view you don't put more energy into the snow by having legs bent, but it sure takes effort

 

Can it also be said that cross-over is more effective when it comes to controlling speed? Since you actually push the CoM uphill when you extend?

post #13 of 21
In cross through, your feet are ahead of you at the transition, but that doesn't necessarily mean that you have to support yourself with your quads as though you were sitting against a wall. Don't forget the virtual bump. As you go from one turn to the next there is energy at work that you can direct to your lower legs as you absorb the bump by letting your hips stay low and letting your feet come up over the virutal bump and cross to the other side of the CoM.

When you extend your legs after transition, let your skis track outside of your CoM as your CoM continues diagnonally down the hill (the direction it was heading when you released your last turn). There might be an uphill force component once you pass the apex of the turn, but the vast majority of the force should be across the hill. This is why racers try to maximize their pressure at the apex, not after it; so they aren't pushing themselves up the hill (slowing down), but pushing their CoM towards the next turn across the slope.

If you were in cross through at transition, your CoM is catching up with your feet on the way to the apex of the turn as your feet take the longer track as you approach the apex of the turn. If you were in cross over, your CoM can be, but doesn't have to be, forward of your feet at the apex; you have more options for CoM location and leg extension with cross over than with cross through without resorting to extreme athletics. As you extend from transition, you let the pressure build on your skis so that at the apex of the turn you can still push more (if you were careful to to fully extend too soon) when you need a tighter turn or you can begin to release pressure when you have changed direction sufficiently.

Racers, exemplified by Bode, will utilize cross through a lot. Cross through utilizes the extremes of balanced positions as getting over the skis requires the CoM to move a fair distance from transition (behind the feet) to apex (over or ahead of the feet). Recreational skiers are better served to try to maintain cross over as it keeps them in a balance zone centralized over the feet.

Pushing your CoM up the hill to slow down is going to be very tiring as you are opposing centrifugal forces and gravity. Let the skeletel stack support you and let the direction and force of the skis in the snow, slow you down. Letting your skis skid (brushed turns) is also a good method for speed control that doesn't require great muscular exertion.
post #14 of 21
Note:
No kittens where sacrificed to any trains during the construction of this post!!
post #15 of 21
Thread Starter 
A consequence that hasn't been explored yet is where the race should start. Do we wait until the last few meters of the turn and use a lot of internal motive force to thrust us across the skis? Do we start the transition earlier so we can use more external motive forces?
Obviously a longer transition would not include the rapid accelerations near the end of the turn and would be easier to manage but can we rely on those external forces to cause enough acceleration to actually carry us through the edge change and into the new turn?
post #16 of 21
Quote:
Originally Posted by MastersRacer View Post


Racers, exemplified by Bode, will utilize cross through a lot. Cross through utilizes the extremes of balanced positions as getting over the skis requires the CoM to move a fair distance from transition (behind the feet) to apex (over or ahead of the feet). Recreational skiers are better served to try to maintain cross over as it keeps them in a balance zone centralized over the feet.

 

Thanks, MastersRacer.     I've been promoting this idea here at Epic for awhile now.  With so many recreational skiers suffering from backseatitis, cross over is the best road to a fix.  Cross through just introduces, and momentarily requires, what they're trying to overcome.  Learn how to get the hips forward (cross over) first.  Learn how to restore that position from hips aft (cross through) later.
post #17 of 21
Quote:
Originally Posted by justanotherskipro View Post

A consequence that hasn't been explored yet is where the race should start. Do we wait until the last few meters of the turn and use a lot of internal motive force to thrust us across the skis? Do we start the transition earlier so we can use more external motive forces?
Obviously a longer transition would not include the rapid accelerations near the end of the turn and would be easier to manage but can we rely on those external forces to cause enough acceleration to actually carry us through the edge change and into the new turn?

If your feet reach the transition before you do, just have patience to get your feet back under the body in the next turn. Don't fight it in the existing turn. Racers make a lot of their recoveries at  transition and in the turn that follows, not in the actual turn that was bobbled. (I almost put too many 'ohs' and too few 'bees' in that last word! ) In the bobbled (did it again! ) turn they just make sure they survive so they can recover in the next turn.

Unless you really goof up, you are going to have enough momentum to get to the next turn. It is just that the next turn's shape may have to be adjusted to deal with the consequences of the last one. I'd visualize getting my feet back under me rather than me back over my feet. This can be done by pulling back the feet after transition or by tightening the turn so that the centrifugal forces will 'push' my CoM back over the feet or by starting the turn sooner, with the same result as tightening the turn.
post #18 of 21
Thread Starter 
Conserving momentum and allowing external motive forces to carry the body through the transition without adding any internal motive forces or adding some braking to change the speed of either the CoM or the BoS is an idea BB's been talking about for quite some time. While it gets suggested that a cross over with a vertical displacement of the pelvis needs an active internal motive force, I've found that it's not all that necessary if the CoM doesn't remain too far inside the turn, too late in the turn. Even without any active flexing of the outside leg or a strong extension of the new outside leg. Making both transitions very efficient.
Edited by justanotherskipro - 1/29/10 at 5:00pm
post #19 of 21
Thread Starter 
Now that isn't meant to suggest this is type of transition is anything more than one option. Sliding the feet forward, or actively moving the hips diagonaly forward and towards the new turn are other options as well. What's interesting to me is trying to use all of these options in a variety of different situations. Some work out well, other blow up in your face and some almost cause you to crash. To me that's the point of playing with different movements.
Edited by justanotherskipro - 1/29/10 at 6:11pm
post #20 of 21
 It's good. I like it.
post #21 of 21
Quote:
Originally Posted by justanotherskipro View Post

Do we really need a disclaimer here? How silly! The visual image comes from an old movie stunt not from any suggestion to literally race a train. It points out how out of context an idea can be taken when it's intepreted as more than it is.

Not out of context, as I well understand the metaphor.  I and my coworkers at FRA try to take every opportunity to raise awareness of Highway Rail grade crossing safety.  if you want to see the home crowd get really upset you should see what happens when a movie shows kids fishing happily from a railroad bridge.  I think most of my coworkers, and I, as well, just believe that a little more awareness might save a couple of lives.  In short, I was looking for a PSA opportunity.
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