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Edge angle comes from two source, inclination and knee angulation/foot tipping - Page 2

post #31 of 58
Quote:
Originally Posted by Cgrandy View Post
 

While sitting at your desk,  place your feet together and then lift them off the floor.

 

Rotate your feet side to side (imagine skidded turns ;-)

 

Observe what happens at the knees!

 

Nearly nothing!...but something....

Go ahead,  place your fingers just over the knee cap,  feel the "rotation".  ;-)

Do the same but keep the feet pointing forward and notice that the knee must move

post #32 of 58
Quote:
Originally Posted by tdk6 View Post
 

 

Bingo. This is what I have been trying to explain many times before. The primary movement at the ankle is indeed rotation. Not tipping. 

You cannot have one without the other. There is no biomechanical "rotate only" capability in the ankle. Note though that the fore part of the foot does not have to tip. The foot is not a rigid structure. I has many joints. If the ankle bones are in contact with the shell so you cannot tip the ankle at all you will have a very poor balance.

 

Quote:

Originally Posted by tdk6 View Post
 

 

 

 

 

 

 

 

 

IMO you don't have a lot of side bending force at the knee when you are in the back. Really forward yes, but not in the back seat. And yes, tipping can be very harmful for your knees if you have your weight forward like you describe.

 

 

 

Imagine that you have plane defined by the center joint points of the ankle, knee and hip. The sideways bending force in the knee is directly proportional to the distance of the forces to this plane.

For example if the force passes through the ankle and the hip, i.e. stacked balance, the force lies in this plane so there is no sideways bending force. As long as this condition is true it does not matter how much you point the knee because you are moving the plane with it.

 

If the force passes through the balls and the hip joint center, then there will be a sideways bending force (moment).

 

Similarly if you are really back, but since the heel is much closer to the ankle we are really talking about hanging off the cuffs so the force comes behind the heel.

 

Quote:

Originally Posted by tdk6 View Post
 

 

Your spelling is for me funny here so I maybe miss something but if you are in balance with the forces at play in a carved turn and you angulate without moving your hips into the turn but instead only lean outwards sideways with your upper body at the waist/hip, you shift your CoM towards the outside and that upsets your balance towards the outside. If you increase your edge angles in this state by for example tipping your feet with no other movements then you will be in an even more unbalanced position. Increasing edge angles increases turn forces and must be evened out by moving your CoM towards the inside of the turn. If you move your CoM towards the inside of the turn you need to compensate by increasing edge angles. Works both ways. Playing with these components you maintain your lateral balance.

 

So, it depends on how we define Hip Angulation. Only the angle between upper and lower body or tilting our legs into the turn while moving our hips in that direction as we lean towards the outside of the turn to maintain a balanced stance. But I agree, the title should include Hip Angulation as the 3rd component for increased edge angles as that is probably the most common perception of the word Hip Angulat

 

Yes it depends on the definition. I just thought it would be weird if we define knee/ankle angulation different than hip angulation. Glad we agree:beercheer:

post #33 of 58
Quote:
Originally Posted by Jamt View Post
 

Do the same but keep the feet pointing forward and notice that the knee must move

The knee moves because of femur rotation, a knee is a hinge mechanism, it doesn't move sideways. The lateral range of motion of a knee is like 5 millimeters, to prevent injury's. Just perform a valgus and a varus test to see how much lateral range of motion your knee has.

If your knees are pointing sideways, towards where you are going, they are simply following the femur that is rotating in the hip socket.

Knee angulation basically means the angle of the femur compared to your ski's is not the same as the angle between the tibia and your ski's anymore, putting the knee in a weak position, because the muscles around the femur are not in a proper angle to absorb the forces and support the knee joint. Knee angulation is however a poor term, because this form of angulation also happens by twisting the femur in the hip socket and not because of the non existing lateral range of motiong of a knee.

The difference between hip angulation and knee angulation is that hip angulation moves the femur towards the outside of the turn, which means if you turn left, you allow your legs to move right due to the femur moving in the hip socket. With 'knee angulation' (which is still hip angulation) your move the femur towards the inside of the turn. So if you turn left, you force the femur to move left as well, instead of allowing it to move away from you. So basically 'knee angulation' is reversed hip angulation.

Another way to look at it is this: Knee angulation is rotation from the hip socket towards the inside of a turn. Hip angulation is more like tipping from the hip socket. Tipping from the hip socket results in your hips being inside of the turn compared to your knees. Hip socket rotation towards the inside of the turn results in your knees being inside of the turn compared to hips (if you exaggerate enough).

So yes, in all cases the knee has to move. But it is not the knee itself that is moving, the knee is merely following the rest of your leg. The hip socket however has a very very large range of motion and that is where all the movement is coming from.


Edited by Art of Skiing - 3/22/16 at 1:29am
post #34 of 58
Thread Starter 
Quote:
Originally Posted by Cgrandy View Post
 

While sitting at your desk,  place your feet together and then lift them off the floor.

 

Rotate your feet side to side (imagine skidded turns ;-)

 

Observe what happens at the knees!

 

Nearly nothing!...but something....

Go ahead,  place your fingers just over the knee cap,  feel the "rotation".  ;-)

 

Yes, good test. There is some rotation of the tibia at the knee. Most however at the ankle. Or?

post #35 of 58
Thread Starter 
Quote:
Originally Posted by Jamt View Post
 

Do the same but keep the feet pointing forward and notice that the knee must move

 

Don't understand. Are you saying that instead of keeping our knees pointing forward and twisting our feet back and forth on the floor we lock the feet to the floor and let our knees point from side to side rotating at the hip socket?

post #36 of 58
Quote:
Originally Posted by tdk6 View Post
 

 

Don't understand. Are you saying that instead of keeping our knees pointing forward and twisting our feet back and forth on the floor we lock the feet to the floor and let our knees point from side to side rotating at the hip socket?

They don't need to be locked on the floor, but essentially yes.

post #37 of 58
Quote:
Originally Posted by Art of Skiing View Post
 

The knee moves because of femur rotation, a knee is a hinge mechanism, it doesn't move sideways. The lateral range of motion of a knee is like 5 millimeters, to prevent injury's. Just perform a valgus and a varus test to see how much lateral range of motion your knee has.

If your knees are pointing sideways, towards where you are going, they are simply following the femur that is rotating in the hip socket.

Knee angulation basically means the angle of the femur compared to your ski's is not the same as the angle between the tibia and your ski's anymore, putting the knee in a weak position, because the muscles around the femur are not in a proper angle to absorb the forces and support the knee joint. Knee angulation is however a poor term, because this form of angulation also happens by twisting the femur in the hip socket and not because of the non existing lateral range of motiong of a knee.

The difference between hip angulation and knee angulation is that hip angulation moves the femur towards the outside of the turn, which means if you turn left, you allow your legs to move right due to the femur moving in the hip socket. With 'knee angulation' (which is still hip angulation) your move the femur towards the inside of the turn. So if you turn left, you force the femur to move left as well, instead of allowing it to move away from you. So basically 'knee angulation' is reversed hip angulation.

Another way to look at it is this: Knee angulation is rotation from the hip socket towards the inside of a turn. Hip angulation is more like tipping from the hip socket. Tipping from the hip socket results in your hips being inside of the turn compared to your knees. Hip socket rotation towards the inside of the turn results in your knees being inside of the turn compared to hips (if you exaggerate enough).

So yes, in all cases the knee has to move. But it is not the knee itself that is moving, the knee is merely following the rest of your leg. The hip socket however has a very very large range of motion and that is where all the movement is coming from.

Where did I say that the knee bends sideways? Move and bend are not the same.

 

Also I think your definition of moving the femur towards the outside of the turn when hip angulating is a bit unusual. Normally the reference is the ski, and then the femur moves inside the turn.

 

Knee angulation is not only rotation from the hip socket. The ankle complex is also involved.

 

About the weak position, see my previous post about sideways bending moment. It is not as simple as "always weak".

post #38 of 58
Quote:
Originally Posted by Jamt View Post
Quote:
Originally Posted by tdk6 View Post
 

 

Bingo. This is what I have been trying to explain many times before. The primary movement at the ankle is indeed rotation. Not tipping. 

You cannot have one without the other. There is no biomechanical "rotate only" capability in the ankle. Note though that the fore part of the foot does not have to tip. The foot is not a rigid structure. I has many joints. If the ankle bones are in contact with the shell so you cannot tip the ankle at all you will have a very poor balance.

 

 

I realized that the term tip the ankle is not very accurate. The tipping happens in the subtalar joint, which is basically a torque converter, so when the foot tips the ankle is rotating around an axis similar to the tibia. In other words the ankles bones sticking out, the malleoluses, move forward and aft, not laterally. (they move a bit lateral but that is due to following the tibia/boot)

 

So, I would suppose then that it is "more" fine to restrict the lateral movement of the ankle, but it should be allowed to rotate a bit.

post #39 of 58
Thread Starter 

Quote:

Originally Posted by Jamt View Post
 

They don't need to be locked on the floor, but essentially yes.

 

I think Cgrandy ment to say that the tibia rotates some at the knee. The knee only bends in one plane but it allows for some rotation.

post #40 of 58
Thread Starter 
Quote:
Originally Posted by Jamt View Post

 

I realized that the term tip the ankle is not very accurate. The tipping happens in the subtalar joint, which is basically a torque converter, so when the foot tips the ankle is rotating around an axis similar to the tibia. In other words the ankles bones sticking out, the malleoluses, move forward and aft, not laterally. (they move a bit lateral but that is due to following the tibia/boot)

 

Exactly. I have had lots of work done to my boots to allow my outside fibula ankle bone to rotate backwards when I tip the inside foot into the turn.

 

 

Quote:

Originally Posted by Jamt View Post

 

So, I would suppose then that it is "more" fine to restrict the lateral movement of the ankle, but it should be allowed to rotate a bit.

 

I think it rotates quite a bit.

post #41 of 58
Quote:
Originally Posted by tdk6 View Post
 

Quote:

 

I think Cgrandy ment to say that the tibia rotates some at the knee. The knee only bends in one plane but it allows for some rotation.

Google Screw Home Test/Mechanism of the Knee.  You will learn that there is about ten degrees of rotation femur to tibia.  The mechanism is quite complex and worth a read.    YM

post #42 of 58

Might this image help?

post #43 of 58
Quote:
Originally Posted by tdk6 View Post
 

 

I think it rotates quite a bit.

Well, you are the one saying that the foot cannot tip because it is in a snug boot, and the ankle cannot rotate unless the "lower" foot tips. 

post #44 of 58
Quote:
Originally Posted by yogaman View Post
 

Google Screw Home Test/Mechanism of the Knee.  You will learn that there is about ten degrees of rotation femur to tibia.  The mechanism is quite complex and worth a read.    YM

As far as I know this is related to knee lock-out mechanism so not very related to skiing.

 

There is some tibia-femural rotation possible with bent knee also, but IMO this only occurs if you knee-push and it is not something I would advice.

I don't think this is very well known. During a level 2 coach clinic I attended a number of years ago this subject came up in the biomechanical part, and the clinic leaders did not know how/if it was used in skiing, and an orthopedic MD who was one of the participants could not give an answer either.

post #45 of 58
Thread Starter 
Quote:
Originally Posted by Jamt View Post
 

Well, you are the one saying that the foot cannot tip because it is in a snug boot, and the ankle cannot rotate unless the "lower" foot tips. 

 

I still don't think the foot can tip much inside the boot. But I do think that tipping the foot inside the boot tips and rotates the tibia. Here a picture where I tip only the inside foot on its LTE.

 

 

We cant see what is happening inside the boot but I think its quite easy to see that the tibia had to rotate at the ankle and some at the knee and the femur at the hip socket since the boot is still pointing in the exact same direction it was before tipping. If I lifted up my tipped inside right ski off the snow the ski would align itself to the direction of where my knee is pointing.

post #46 of 58
Quote:
Originally Posted by tdk6 View Post
 

 

I still don't think the foot can tip much inside the boot. But I do think that tipping the foot inside the boot tips and rotates the tibia. Here a picture where I tip only the inside foot on its LTE.

 

 

We cant see what is happening inside the boot but I think its quite easy to see that the tibia had to rotate at the ankle and some at the knee and the femur at the hip socket since the boot is still pointing in the exact same direction it was before tipping. If I lifted up my tipped inside right ski off the snow the ski would align itself to the direction of where my knee is pointing.

Then you are knee pushing. I can tip while lifting the ski, and I don't want to tip it any more than that, although I could. Knee pushing is like trying to pre-release the binding.

 

If you look carefully at the picture you can see that the tibia has also rotated inside the cuff, hence there is no need for tibia-femural rotation. You can feel this by grabbing you lower leg hard with your hands. You can still twist them around due to the soft tissue in the lower leg.

 

When loaded an not exaggerating we are probably talking about less than 5 degrees, but it is still enough for force alignment.

post #47 of 58
Tdk just go straight on a flat trail and tip your foot towards little toe. While it's on the ground. If you allow your body to go you will start turing that direction. You can prevent it, but don't. Then play with both feet on ground but mainly supported by one. Pretty wide stance. Tip one foot towards little toe then back to bjg toe and continue. You'll roll the ski from outside edge to inside edge. Nice warmup for feet/ ankles.

Tipping the foot changes where the balance lines are in the foot and how the foot is loaded. If you lock that out it greatly affects balance. I tried once having a rigid footbed made. Had fiberglass in the arch. Oh, one day on that my knees hurt for over a week.
I suspect a fair number of junior racers have locked up their ceet by overly constrictive boots. Essentially they are skiing with club feet. Like pieces of wood. That is not good.
Quote:
If the ankle bones are in contact with the shell so you cannot tip the ankle at all you will have a very poor balance. - Jamt
If you only get one thing out of this thread, get that. And locking up the feet, or having them numb, is bad.
post #48 of 58

Something we need to remembering is that movement is relative. What is the movement in relationship to the edge angles? How much movement does it take to affect a change in the physics of the ski? etc..

 

People on this thread keep talking about "locked up" ankles, snug boots, stiff boots, knee only bends xyz, etc.

 

Just extremely small amount of muscle contraction inside the boot when we try to articulate the ankle is enough to change the forces being created. These forces will also trigger some feedback which will affect how we balance or make adjustments. Just the act of beginning to flex, extend, articulate (evert or invert) our ankles will begin a chain of actions that will affect our balance, how we move and what we do to our skis.

 

It's not something we have to be able to "see". It does however affect how we ski and in this case specifically edge our skis.

post #49 of 58
Quote:
Originally Posted by dchan View Post
 

Something we need to remembering is that movement is relative. What is the movement in relationship to the edge angles? How much movement does it take to affect a change in the physics of the ski? etc..

 

People on this thread keep talking about "locked up" ankles, snug boots, stiff boots, knee only bends xyz, etc.

 

Just extremely small amount of muscle contraction inside the boot when we try to articulate the ankle is enough to change the forces being created. These forces will also trigger some feedback which will affect how we balance or make adjustments. Just the act of beginning to flex, extend, articulate (evert or invert) our ankles will begin a chain of actions that will affect our balance, how we move and what we do to our skis.

 

It's not something we have to be able to "see". It does however affect how we ski and in this case specifically edge our skis.

 

dchan, this is a great insight to interject into this type of discussion. The initiative of all movement starts at the feet/ankles. While at times it seems to be ignored, perhaps due that its hidden nature and not really allowed to move very much, it is these very factors that makes what happens inside the shell so relevant to the inception of all following motor adjustments. It is the nerve center that dictates how all the other following movement patterns will be characterized through its DIRT. That the ankle cannot move very much before applying its wealth of input (and output) speaks to its superior immediacy of both terrain based input detection and the immediacy of its output response that resonates up the chain. The ski boot is both the first and final word between what transfers between body and ski. This also speaks to the value of a balance board, where like skiing, the ankle is, bio-mechanically speaking, top dog.

post #50 of 58
Quote:
Originally Posted by Jamt View Post

When loaded an not exaggerating we are probably talking about less than 5 degrees, but it is still enough for force alignment.
Consider my "movement is relative" comments and then think about this.

Many of us are thinking about a .5 degree change in edge angles when we tune our skis! Some complain on how grabby or grippy .5 degrees of base bevel or side bevel can make a ski feel, or how not enough (also in the sub 1 degrees range) can make a ski feel "unskiable" or "unable to hold an edge" And here you are thinking in terms of 3-5 degrees of movement may not be enough?

It's still edging and affecting edge angles and it's still inclination or angulation. Just because we can't see it clearly, doesn't mean it's not happening or affecting the ski snow interaction or performance. It's just that when doing movement analysis, we are seeing the outcome of these minute movements, not the actual movements themselves.
post #51 of 58
Well tires and tire pressure will greatly effect car handling. Like a base bevel.
post #52 of 58
Quote:
Originally Posted by razie View Post
 

Inclination and angulation do not describe movements but... uhh... I still struggle with classifying these two... results of other movements?

 

Having the skis on edge requires inclination of COM to balance against the forces and angulation to balance some more and allow the desired edging... but many see it backwards and focus too much on dragging the skis on edge with the upper body - which is problem no 1 with skiers.

 

The proper movements though start from the feet up. A good expert skier will maintain counter in transition and decouple the feet from the hips (do we call this now WC style?) and then all you need to do, as the hips move down the hill, is to put the skis on edge with the feet, as the skis move sideways, before the hips move down far enough to drag them on edge. In this realm now, of high level skiing, the movements are different.

 

I don't like thinking that edge angle is a side effect from some other movement or concept... like "inclination". It is its own movement, in high level skiing and it starts in the feet and ankles. The legs just couple and decouple the feet from the hips, as needed, via flexing and extending as needed:

 

cheers

Razie.  You are absolutely right.   Obtaining, building and controlling edge is what it is all about and as you so rightly implied, we can obtain edge in various ways depending on a host of variables including one's personal preference. 

 

One thing I do want to throw out for consideration is that edging is arrived at differently depending on what force (Gravity/Centripetal) is dominant. 

 

JF says,  Edging happens as a RESULT of the inside leg getting shorter.  I agree with that statement although I will add the caveat that the inside leg is passively shorter while balancing against gravity but be we actively make the inside leg shorter to increase edge angle to deepen the turn and  build centripetal force. 

post #53 of 58
Quote:
Originally Posted by dchan View Post

And here you are thinking in terms of 3-5 degrees of movement may not be enough?

 

Maybe you read what I wrote too fast? I just stated that it IS enough.

 

Quote:
Originally Posted by Jamt View Post

When loaded an not exaggerating we are probably talking about less than 5 degrees, but it is still enough for force alignment.
post #54 of 58
Quote:
Originally Posted by Jamt View Post
 

Maybe you read what I wrote too fast? I just stated that it IS enough.

 


Oh, I read it well enough and I totally agree. That comment was aimed at your detractors.. My comment was meant that 3-5 should be WAY more than enough and we need to start putting this in some sort of perspective. Several people were commenting on "how stiff my boot is" or "how snug my boot is so I can't articulate" blah blah blah. 1 degree of movement is enough considering many complain that .5 or 1 degree on the base or side changes the way a ski feels or skis.

 

DC

post #55 of 58
Thread Starter 
Quote:
Originally Posted by Tog View Post

Tdk just go straight on a flat trail and tip your foot towards little toe. While it's on the ground. If you allow your body to go you will start turing that direction. You can prevent it, but don't. Then play with both feet on ground but mainly supported by one. Pretty wide stance. Tip one foot towards little toe then back to bjg toe and continue. You'll roll the ski from outside edge to inside edge. Nice warmup for feet/ ankles.

Tipping the foot changes where the balance lines are in the foot and how the foot is loaded. If you lock that out it greatly affects balance. I tried once having a rigid footbed made. Had fiberglass in the arch. Oh, one day on that my knees hurt for over a week.
I suspect a fair number of junior racers have locked up their ceet by overly constrictive boots. Essentially they are skiing with club feet. Like pieces of wood. That is not good.
If you only get one thing out of this thread, get that. And locking up the feet, or having them numb, is bad.

 

Right on the money. Rolling that foot from LTE to BTE while gliding straight forward is a great drill. The picture I posted kind of represents the moment the foot is tipped to its LTE. Ive been using a soft footbead for the last 15 years or so and have had my boots modified so that my ankle bones don't hurt against the shell when moving around, mainly rotating backwards when I tip my inside ski to its LTE.

post #56 of 58
Thread Starter 
Quote:
Originally Posted by Jamt View Post
 

Then you are knee pushing. I can tip while lifting the ski, and I don't want to tip it any more than that, although I could. Knee pushing is like trying to pre-release the binding.

 

Im not knee pushing. I can also lift the ski up in the air and tip my foot and easily hold it there. You have probably not considered the fact that tipping that inside foot causes your front part of your foot, the ones with the toes, to point in the opposite direction of where you are tipping. So when you are tipping your inside foot to its LTE try to pay close attention to what happens to that part of the foot. It pivots in the other direction. The same holds true for the outside foot. There the movement is reversed. If you are tipping your foot in the same manner your trying to pre-release the binding its definitely wrong.

 

Quote:
Originally Posted by Jamt View Post
 

If you look carefully at the picture you can see that the tibia has also rotated inside the cuff, hence there is no need for tibia-femural rotation. You can feel this by grabbing you lower leg hard with your hands. You can still twist them around due to the soft tissue in the lower leg.

 

When loaded an not exaggerating we are probably talking about less than 5 degrees, but it is still enough for force alignment.

 

I was not saying there is a lot of tibia/femoral rotation. Just that there can be and probably there is. The main part of the rotation comes from the ankle just as you mentioned. I have actually previously considered tibia/femoral rotation at all. Personally my own knee ligaments are quite rigid so I feel very little rotation myself.

post #57 of 58
Quote:
Originally Posted by tdk6 View Post

You have probably not considered the fact that tipping that inside foot causes your front part of your foot, the ones with the toes, to point in the opposite direction of where you are tipping.
Off course I have. Didn't I just say that you cannot rotate without tipping. It is the same thing.I have shown the picture of the torque converter many times
post #58 of 58
Thread Starter 
Quote:
Originally Posted by Jamt View Post


Off course I have. Didn't I just say that you cannot rotate without tipping. It is the same thing.I have shown the picture of the torque converter many times

 

Good to hear as its something people usually don't seem to acknowledge. Haven't seen it here before. Here is the picture I drew a while back. I modified it a bit. Drew the centreline's thicker and offset them at the ankle and the hip in the far right picture to better display the rotation taking place.

 

 

A2 Normal stance

B2 Inclined stance (could be with or without Angulation)

C2 Inclined stance with foot tipping (could be with or without Angulation)

 

The picture is not necessarily meant to show a progression even if it very well could be such. First we incline before we add foot tipping and femur rotation to be sure our edges are engaged as there could otherwise be a risk for a pivot entry. Here below I tried to display a situation where the turn started by tipping the feet first. If you are aware of the twisting action of the feet there is no risk for a pivot entry.

 

Note that there is only a limited range of rotation at the ankle and its quickly used. 

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