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Fore/Aft Balance and Physics

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karlo

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Which gets to my “effective edge”. It’s the piece of edge that, infinitesimally small increments that is in contact AND has pressure.

That is poorly stated. Help me here in how to state what I mean. I don’t mean that the pressure is only on that newly engaged, infinitely small piece

But, also, one more thought. Shifting pressure from fore to aft allows us to impart our own energy into the skis at the exit of a turn, e.g., to bend the tip more than it otherwise would bend, if that’s what we would like. Going fore is like coiling the spring. Going from fore to aft is like the release of the stored energy into the skis. That’s the propulsion I’ve been working on. If we just stay centered, that’d be like trying to throw a ball, sorry, like a girl, no wind up. So sorry, but it’s a valid generalization, though one that isn’t doing me any favors.
 
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Doby Man

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I find these two above photos that Razie posted of two notably different skill levels skiing the same turn, same snow, same everything which provides itself as an excellent comparison regarding the following comments.

The biggest fundamental difference that I see between these two skiers is that the above skier, Rob Kelly, is skiing on two skis and the below skier is skiing on only one ski. The bottom skier is obviously suffering enough tip lead that his inside ski is not part of the turning process at all, the inside leg, foot and ski becoming a useless appendage. The key movement pattern here is equal dorsiflexion vs unequal dorsiflexion. Because equal dorsiflexion keeps the inside ski back, the Com is more forward resulting in being balanced over the middle of the ski as indicated by ski bend and snow spray. The above position is balanced, relaxed, strong and confident while the below skier, through simply not dorsiflexing the inside ski, is suffering an obvious fit of strife, reaching forward and bending forward yet to no avail as it results in even more pressure on the tail. This is a case where any attempt at a pullback correction at or after this shot will be too late to offer any reprieve to w3hat has already happened. This much tip lead also makes it difficult maintaining equal tipping which takes the inside ski even further off track with the outside ski, further compounding the issue. This comparison is an excellent depiction of how much can go wrong without the right fundamental movements of modern technical freeskiing and racing such as equal dorsiflexion, equal tipping and equally advancing skis.

Once a skier has learned how to ski with all their balance on the outside ski, they should immediately start working on reintroducing the inside ski with all the same parameters as the outside ski except for pressure distribution with the bulk of that amplitude going to the outside ski. When a skier keeps shifting 100% pressure from ski to ski, there is no ability to dorsiflex the inside ski the way that Kelly does.
 
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Mike King

Mike King

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Oh, what gave me up? This?



...about the two guys above - well, there's the gate, the skis are both engaged and in the fall line and I'm filming from the side. That's a steep double black like-injected run Not sure what more you would need for your dynamic analysis? They clearly turn on the same foot... :)

Your hypothesis in the OP was that as the ski moves into the fall line, it accelerates and they both need to move forward to keep applying pressure to the middle of the ski.

Yet both have clearly moved forward along the ski but one applies pressure forward of middle and the other back of middle.
You still cannot tell what the acceleration is. You’ve assume both have the skis moving along the length of the ski, yet one shows that is not the case. The skis will accelerate into the fall line if they are bent and moving along there length. Your skier is showing a fair amount of lateral travel. But is it accelerating? Decelerating? We can’t tell from a single frame.

My suspicion is that because of the excess tip lead he has, he is so far forward that the tail is not traveling the same path as the tip. Video would be required to ascertain this.

Mike
 

Rod9301

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I find these two above photos that Razie posted of two notably different skill levels skiing the same turn, same snow, same everything which provides itself as an excellent comparison regarding the following comments.

The biggest fundamental difference that I see between these two skiers is that the above skier, Rob Kelly, is skiing on two skis and the below skier is skiing on only one ski. The bottom skier is obviously suffering enough tip lead that his inside ski is not part of the turning process at all, the inside leg, foot and ski becoming a useless appendage. The key movement pattern here is equal dorsiflexion vs unequal dorsiflexion. Because equal dorsiflexion keeps the inside ski back, the Com is more forward resulting in being balanced over the middle of the ski as indicated by ski bend and snow spray. The above position is balanced, relaxed, strong and confident while the below skier, through simply not dorsiflexing the inside ski, is suffering an obvious fit of strife, reaching forward and bending forward yet to no avail as it results in even more pressure on the tail. This is a case where any attempt at a pullback correction at or after this shot will be too late to offer any reprieve to w3hat has already happened. This much tip lead also makes it difficult maintaining equal tipping which takes the inside ski even further off track with the outside ski, further compounding the issue. This comparison is an excellent depiction of how much can go wrong without the right fundamental movements of modern technical freeskiing and racing such as equal dorsiflexion, equal tipping and equally advancing skis.

Once a skier has learned how to ski with all their balance on the outside ski, they should immediately start working on reintroducing the inside ski with all the same parameters as the outside ski except for pressure distribution with the bulk of that amplitude going to the outside ski. When a skier keeps shifting 100% pressure from ski to ski, there is no ability to dorsiflex the inside ski the way that Kelly does.
Not true at all. You can have 100 percent weight on the outside do and pull the inside foot back.
 

Erik Timmerman

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Not true at all. You can have 100 percent weight on the outside do and pull the inside foot back.

What did Doby Man say that is untrue? He didn't say Robby is weighting that ski, he said he is skiing it. Did I miss some other statement?
 

razie

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the above skier
is skiing on two skis

[...]

Because equal dorsiflexion keeps the inside ski back, the Com is more forward resulting in being balanced over the middle of the ski as indicated by ski bend and snow spray.

reintroducing the inside ski with all the same parameters as the outside ski except for pressure distribution with the bulk of that amplitude going to the outside ski. When a skier keeps shifting 100% pressure from ski to ski, there is no ability to dorsiflex the inside ski the way that Kelly does.

So you're saying that to keep the inside ski back as much as needed, it needs to be weighted? Probably to flex the boot? Same amount as the outside boot, you're suggesting?

First skier - his snow spray clearly stops before the heel of the boot, so he is clearly pressuring the forebody of the ski, not the middle.

Also, you would largely be correct if the below skier made the technical error that you described, often enough in free ski or courses. He doesn't. It's a common tactical error that got him there - race coaches are probably smiling when seeing that :)

But to clarify, if there was any doubt at this point about the topic that we're discussing here: he is back, although he is forward in the respective plane...

@Mike King so you are saying that the acceleration of the ski relative to the hips is important. Let's say for the sake of simplifying the argument that I am staying square to the skis. How can the ski accelerate faster than the hips into the fall line if I don't get back in the fore/aft plane?
 

razie

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the above skier
is skiing on two skis

[...]

Because equal dorsiflexion keeps the inside ski back, the Com is more forward resulting in being balanced over the middle of the ski as indicated by ski bend and snow spray.

reintroducing the inside ski with all the same parameters as the outside ski except for pressure distribution with the bulk of that amplitude going to the outside ski. When a skier keeps shifting 100% pressure from ski to ski, there is no ability to dorsiflex the inside ski the way that Kelly does.

So you're saying that to keep the inside ski back as much as needed, it needs to be weighted? Probably to flex the boot? Same amount as the outside boot, you're suggesting, to allow the same dorsiflexion? I can see that theory hitting "the wall" pretty soon ;)

First skier - his snow spray clearly stops before the heel of the boot, so he is clearly pressuring the forebody of the ski, not the middle.

Also, you would be correct in some regards, if the below skier made the technical error that you described, often enough in free ski or courses. He doesn't. It's a common tactical error that got him there - race coaches are probably smiling when seeing that :)

But to clarify, if there was any doubt at this point about the topic that we're discussing here: he is back, although he is forward in the respective plane...

@Mike King so you are saying that the acceleration of the ski relative to the hips is important. Let's say for the sake of simplifying the argument that I am staying square to the skis. How can the ski accelerate faster than the hips into the fall line if I don't get back in the fore/aft plane?

@Erik Timmerman - that's virtually all he says there... that you can't ski it unless you weight it, to get equal tipping and dorsiflexion:

When a skier keeps shifting 100% pressure from ski to ski, there is no ability to dorsiflex the inside ski the way that Kelly does.
 
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James

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The bottom skier is lunging with the upper body to clear the gate. He's ended up too far and is over the inside ski. The inside leg is seemingly pretty dorsiflexed, the outside one is lagging behind as there's probably not enough weight on it.
Did he recover for the next gate? I would think so.
Maybe try tying his upper arms to his body?

IMG_5863.PNG
 

karlo

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skis will accelerate into the fall line if they are bent and moving along there length. Your skier is showing a fair amount of lateral travel. But is it accelerating? Decelerating? We can’t tell from a single frame.

Can someone tell me what is meant by “accelerating” and “decelerating “? Velocity of what, relative to what?

Yes, I can see that ski will turn “into the fall line” and turn away from it, but accelerate? To me, a turn is an acceleration; their not two different things
 

Doby Man

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Razie, my post specifically states: "Once a skier has learned how to ski with all their balance on the outside ski, they should immediately start working on reintroducing the inside ski with all the same parameters as the outside ski except for pressure distribution with the bulk of that amplitude going to the outside ski." It is towards the end which is why it helps to read all the way through.

Inside ski engagement requires some pressure so it at least bends as much as the outside ski. When the inside ski is minimally engaged, it is ready to take over at any time such as a white pass turn for which there is no time to think before doing it.

@razie, you are correct that R.K. is pressuring his shovel more than the center of his ski and was only mentioning his forwardly activated ski compared to the below skier. I actually appreciate that shovel carving aspect very much yet find it difficult to find examples like yours of R.K. that show it so well.

@Rod9301, if the skier is not going to engage the inside ski with the snow surface, why even bother to pull it back? That would only very minimally effect overall fore/aft balance/position. But let's not devolve into a pull back thread, that of which we have all asserted our respective positions.

@James, you are correct that the inside leg is dorsiflexed. My point is about unequal dorsiflexion for which the outside ankle is much more flexed that the inside.

I know that when I ski, the DIRT of the ski turning, bending, tipping and fore/aft pressure is the same. Only the inside/outside rate of pressure, is outside dominant. When every turn is so different (momentum centrifugal force, speed radius, slope, etc.), skiing with a 100% weight/pressure/load shift with every turn is not representative of these changes. I allow my weight shift to correspond with the forces of the turn which changes progressively, not all at once. While my biggest load of outside pressure is at the apex and just below (turn phase 2.5), my loads are even at transition. I go from 50/50 at transition to about 10/90 at apex and the tracks show a smooth and progressive weight "shift" in the process.
 

razie

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Raze is your skiers boot particularly soft?
Not really, that one is a red 150.

Inside ski engagement requires some pressure so it at least bends as much as the outside ski. When the inside ski is minimally engaged, it is ready to take over at any time such as a white pass turn for which there is no time to think before doing it.

@Rod9301, if the skier is not going to engage the inside ski with the snow surface, why even bother to pull it back? That would only very minimally effect overall fore/aft balance/position. But let's not devolve into a pull back thread, that of which we have all asserted our respective positions.

@James, you are correct that the inside leg is dorsiflexed. My point is about unequal dorsiflexion for which the outside ankle is much more flexed that the inside.

I know that when I ski, the DIRT of the ski turning, bending, tipping and fore/aft pressure is the same. Only the inside/outside rate of pressure, is outside dominant. When every turn is so different (momentum centrifugal force, speed radius, slope, etc.), skiing with a 100% weight/pressure/load shift with every turn is not representative of these changes. I allow my weight shift to correspond with the forces of the turn which changes progressively, not all at once. While my biggest load of outside pressure is at the apex and just below (turn phase 2.5), my loads are even at transition. I go from 50/50 at transition to about 10/90 at apex and the tracks show a smooth and progressive weight "shift" in the process.

Agreed that most load must be on the outside, I'd say *all* - even at really high edge angles, I see cases like this - she has more dorsiflexion on the inside, quite a lot actually, with virtually no pressure on the ski, as there is light under the boot and the tip not engaged, and checkout the difference in tip bend.

15542320_1509023745793550_8262485068557135153_n.jpg


Or this one - no bend so it's just skimming the surface, even if some spray is coming off it - but also a good example I think of the outside forebody bending more?

52647485_2486501008045814_2459858388964605952_n.jpg
 
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JESinstr

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PSIA Fundamental #2 Control pressure from ski to ski and direct pressure to the outside ski. All three above seem to be doing a pretty good job at that!

About that inside foot being underneath?
1. That's how you maximize angulation vs inclination
2. That's how you keep a large amount of leg mass inline with the COM
3. That's how you position your inside foot to be in the right place to begin the initiation that will take place milliseconds after those images were captured.
 

Doby Man

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Yes Raz, but still shots do not effectively indicate pressure. Yes, snow spray can be misleading as much as it can be illuminating. But so can a ski bending in a still frame because, even when we see light between the ski and ground like the top photo, we do not see if that is the result of a tenth of a second micro deflection where the ski was previously pinned against the snow a micro second before (and after). The physics of ski technique is too complex to make many or most of the assertions I see made in regards to a still frame. While we can see flexion angles, we cannot see what is happening within the flow of that moment, the top picture comments above being an example, and the forces of momentum, speed, gravity, centrifugal, g force, muscular contraction, weight/pressure/load distribution, CoM BoS relationship management, etc., etc.The bottom example of differentiated bending illustrates a good 10% inside - 90% outside in the phase of the turn where most goes to the outside. Though, they are both beautiful turns and something I'm sure we can both agree on.
 

razie

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Well... I wouldn't call that 90/10 - there is no bend in the inside ski...

By simply keeping it close and at those edge angles, it skimming the snow is inevitable because there is simply no room to hide it. That doesn't really make it "voluntary".

However, the issue I take with the notion of "voluntarily" trying to weight the inside ski, is that a) if you think that's how much you apply, you will likely end up with much more than 10 and b) there is no reason to apply it to very little edge angles - I see it as more of an excuse for lack of skill/balance... "Oh yeah, I do that on purpose"... just like the fox and the grapes.

It does take a good deal more skill and balance to do all the good stuff like tipping and dorsiflexion and keeping it back, while also keeping it light... So that what I always teach!
 
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Steve

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So skiing PMTS way is more skilled?

Kind of closed minded dogma.

Different skill blends are not the same as more vs less skill.
 

James

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Yes Raz, but still shots do not effectively indicate pressure. Yes, snow spray can be misleading as much as it can be illuminating. But so can a ski bending in a still frame because, even when we see light between the ski and ground like the top photo, we do not see if that is the result of a tenth of a second micro deflection where the ski was previously pinned against the snow a micro second before (and after).
Yep. Here's Lindsey, apparently doing everything wrong, on her way to a bronze in the 2018 Olympics.
IMG_5864.PNG

Link: youtu.be/ghXI7t70Bnw 1:51
 

razie

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So skiing PMTS way is more skilled?

Kind of closed minded dogma.

Different skill blends are not the same as more vs less skill.

Not what I had in mind, but I guess you could say that - they're big on discipline, that's for sure...

You have to remember that I am a higher level race coach - that's my "good skiing" benchmark!

I will agree with that skill blend statement, when you can do the both extremes and it turns out that you indeed have a choice... until that point, it is not a choice or a blend, just an inability to do X or Y, disguised as "oh, it's just better whichever way I'm doing it - I'm blending it, you see".
 
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