3D Joint Movements

[Zentune]

Generally, a “hollow-backed” skier (anterior pelvic tilt and spinal extension) will have trouble re-supinating/forming and arch with their feet...this is a less strong position to be in...

zenny

 

[karlo]

grf

What's that, grf?

 

[Zentune]

What's that, grf?

Ground reaction force. Sort of like how hard it pushes back at you, or like how a wall in your house pushes back at your hand with exactly the same force that you push at it.

zenny

 

[Doby Man]

I think that is a poor analogy. When I had to do it, it was for the sake of balance. On the other hand, from a recreational skiing point of view, I think I had to do it on account of other deficiencies

I agree with Karlos. A "jumping" analogy doesn't work for skiing.

 

[karlo]

most racers have a rounded back

Today, while skiing, I thought more about what it is about the rounded back. It's not so much that I don't want to do as a racer does. I want to do more as a dancer does, as in ballroom dancing, maybe ballet. To do that, I can't go as fast as many, though I would like to.

 

[Rod9301]

Today, while skiing, I thought more about what it is about the rounded back. It's not so much that I don't want to do as a racer does. I want to do more as a dancer does, as in ballroom dancing, maybe ballet. To do that, I can't go as fast as many, though I would like to.

Keep in mind that an arched back puts a lot of pressure on your lower discs.

Then when you have a shock of any kind the pressure gets amplified.

A rounded back is actually straight in the lower back and slightly curved in the upper back.

Helps with balance for sure, but also puts the spine in a strong position.

But hey, if looks are important to you, go ahead and arch it.

 

[Eleeski]

I agree with Karlos. A "jumping" analogy doesn't work for skiing.

View attachment 36610

That cat's not making the next gate with that body position!

Her body position is not optimal either.

But neither is his.

Eric

 

[karlo]

if looks are important

Yeah, it has come across as if I'm concerned about looks, and I didn't mean that. I mean I don't like, when I have to round my back, the fact that I'm pushing my limits to retain balance as a result of speed/terrain combination. In such a case, I feel like I'm racing and I don't like that feeling. I like the feeling of freefall that is accompanied by a projection down the hill, like a diver tipping forward off a diving platform, that feeling. It's not the feeling of leaning in an effort towards application of great force and achievement of speed. Anyway, that one footed outside ski drill for which I needed to round my back, I found it to be a great drill. And, if I have to round my back to do it, and to improve my skiing, then I accept it.

Regarding the arched lower back, spot on. Over arching it can cause shifts in vertebrae, not good. Strong core is needed to avoid that, and impacts are best absorbed by ankles, knees, and hips.

 

[Chris V.]

We do NOT want to be doing this while skiing, no matter how high our skill level.

Great image. This speaks for itself. If you teach beginners, you're going to see A LOT of this. And thank you to LiquidFeet for the observation that knock-knees and A-framing often result from flaws in pelvic tilt. We often see that knock-kneed posture to an otherwise inexplicable degree, especially in women.

Mark Elling covers this nicely in The All-Mountain Skier.

Notice the dinosaur arms. A dead giveaway. It's an interesting posture. Defensive. Sitting back without really sitting back. A product of an excess of tension, born of anxiety.

I'm resolving to focus more on this issue in lessons. This could address the source of a multitude of problems.

 

[Chris V.]

I liked that last video but rotational separation is not coming from our knees.....

Largely, there's a conflict of semantics going on here. Some of the replies, and some of the linked materials, refer to knee rotation. But in fact the degree to which either the tibia alone or the fibula alone rotates relative to the femur is very small. Rotation of the lower leg is actually a product of the tibia and fibula twisting around each other. Josh, I agree with you, I don't like to call that a knee rotation. I would call it a tib-fib rotation. Some of the linked materials report exact measurements of the amounts of internal and external rotation that are achievable with this movement. Try it, and I think you'll satisfy yourselves that a small amount of this rotation is possible with a fully extended leg, and a considerably larger degree with a flexed knee, probably topping out when the knee is bent about 90 degrees. Maybe some of you guys need to x-ray yourselves to be sure.

It's not the same kind of rotation that one gets from the femur. The hip joint is a universal joint, so the femur actually twists in the hip. Since the attachments of the tibia and fibula to the knee are not universal joints, the lower leg just below the knee twists very little, while the leg just above the ankle twists much more, as a product of the tib-fib rotation.

When we rotate the femurs in the hip sockets, but keep our skis planted in the snow, we get knee angulation. If you stand straight and tall, your ankle, knee, and hip joints will be in approximately a straight line. If you angulate at the knees, your knees are displaced to the side of this line. What is actually happening with each leg is that the femur is rotating in the hip socket in one direction, while the tib-fib rotation is taking place in the opposite direction. The result is edging of the skis. A tib-fib rotation alone doesn't produce good edging, and may actually tip the skis in the opposite of the desired angle.

I think that the video has a weakness insofar as it doesn't say anything about the role of the twisting of the tibia and fibula around each other. Manipulating a skeleton, without ligaments or muscles attached to keep bones in their natural relationship to each other, can be misleading.

 

[Zentune]

“Knee angulation” is a produced by internal rotation at the hip (acetabulum) and ankle (talus/subtalar joint) and a leg that is flexed some at the knee. So technically in tipping-based skiing (carving, arcing) most separation still occurs around the hip joint, with some smaller amount around the lower leg/ankle joint complex. Yes, even with boots on.

This video still has English subtitles I believe....

zenny

 

[karlo]

This video

This is really cool. I tried those positions, leaning on a table. Yes! I can get my knees pointed in a different direction than my feet far more with my knees bent. Is that the cue, when doing movement analysis, that someone is applying rotary movement, rather than just edging and carving, knees pointed in a different direction that feet, feet-following-knees?

 

[Zentune]

Hmmm, well, consider that there is rotary and edging movements in both steering and carving, they are just used and manifest in different ways. For example, if I turn my foot inwardly that is the same as tipping that foot towards it’s little toe edge

zenny

 

[karlo]

Hmmm, well, consider that there is rotary and edging movements in both steering and carving, they are just used and manifest in different ways. For example, if I turn my foot inwardly that is the same as tipping that foot towards it’s little toe edge

zenny

Yes. But does that mean if knees and toes are pointed in the same direction, there is no rotary; it's all edging? And if they are not, there is a rotary component?

 

[Zentune]

If the toes and knees are mostly lined up then that would be akin to active rotary in the classic sense, aka steering. In the video above, opposite directions are discussed, which is more edging, or tipping based although again, there is still separation that is achieved in the rotational, or transverse, plane. There is an “inverse” relationship between foot steering and foot tipping, and in the video I posted he talks about “counter-steering”, so saying “rotary or no rotary” isn’t overly helpful imo. Does that make sense?

zenny

 

[karlo]

Does that make sense?

I need time to think this one through. Next time I'm on the hill, I'll pay more attention to what I am doing when I do a pivot slip (rotary, right?) Then, I'll play with what I feel is more and less rotary in a carved turn, high on edge.

 

[tomgellie]

ummm no....

Knee is a hinge joint.

When the knee is bent its just the femur rotating which is rotating the joint, but the knee itself can not rotate...but if you guys keep saying it because a video said it still will not change these facts. Sitting down right now, with me knees bent if I move my lower leg side to side that is my femur moving. I can put my hand on my upper leg and feel that.

Your knee joints have rotation. Not a lot but it is there and should be for a healthy knee. It is not just a hinge joint. There is rotation between the femoral condyles and the tibial plateau. And most people are scared to use rotation in their knees even though most people do it without thinking anyway. In fact clinically i see a lot of people post ACL surgery that cant fully extend or flex their knee because the rotation that goes with these movements is missing. But if you want to only ski around with flexion and extension present be my guest. But you're missing a level of control, balance and precision.
Feel free to google literature on rotation of the knee joint. here is a video as an example:
ANd dont forget to test rotation in closed chain motion (foot on the ground) as opposed to open chain (foot in the air) which is what everyone on the forum has suggested to do by sitting down with a flexed hip and knee to test. Its very different and you will find that there is more internal rotation possible when the leg is in closed chain. Plus this is far more applicable given when skiing our legs will be acting more in closed chain type motion!

Just found this thread and wanted to add my two cents worth.

 

[tomgellie]

Articulating-Surfaces-of-the-Femur-and-Tibia-at-the-Knee-Joint

• tomgellie
• Mar 3, 2018
• knee joint

Largely, there's a conflict of semantics going on here. Some of the replies, and some of the linked materials, refer to knee rotation. But in fact the degree to which either the tibia alone or the fibula alone rotates relative to the femur is very small. Rotation of the lower leg is actually a product of the tibia and fibula twisting around each other. Josh, I agree with you, I don't like to call that a knee rotation. I would call it a tib-fib rotation. Some of the linked materials report exact measurements of the amounts of internal and external rotation that are achievable with this movement. Try it, and I think you'll satisfy yourselves that a small amount of this rotation is possible with a fully extended leg, and a considerably larger degree with a flexed knee, probably topping out when the knee is bent about 90 degrees. Maybe some of you guys need to x-ray yourselves to be sure.

It's not the same kind of rotation that one gets from the femur. The hip joint is a universal joint, so the femur actually twists in the hip. Since the attachments of the tibia and fibula to the knee are not universal joints, the lower leg just below the knee twists very little, while the leg just above the ankle twists much more, as a product of the tib-fib rotation.

When we rotate the femurs in the hip sockets, but keep our skis planted in the snow, we get knee angulation. If you stand straight and tall, your ankle, knee, and hip joints will be in approximately a straight line. If you angulate at the knees, your knees are displaced to the side of this line. What is actually happening with each leg is that the femur is rotating in the hip socket in one direction, while the tib-fib rotation is taking place in the opposite direction. The result is edging of the skis. A tib-fib rotation alone doesn't produce good edging, and may actually tip the skis in the opposite of the desired angle.

I think that the video has a weakness insofar as it doesn't say anything about the role of the twisting of the tibia and fibula around each other. Manipulating a skeleton, without ligaments or muscles attached to keep bones in their natural relationship to each other, can be misleading.

Nope. The rotation im eluding to is not the tibia and fibula rotating around each other. This rotation would end up showing at the ankle joint. If you check your anatomy the fibula does not create a joint with the femur! it is in fact the tibia and femur opposing each other in rotation. I have tried to create these videos to help educate people on movement found in skiing. There is too much out there in the ski world that ive found is incorrect or some piece of information passed on without clarity and evidence behind it. And id suggest you go out there and test what role the rotation at the lower leg serves....? in performance turns it is essential in getting off the edge cleanly with co-use of the ankles and also in getting the skis to grip early if needed at the top of the turn. Mogul skiers use a lot of lower leg rotation. Pivot slips when performed properly must use the small ammount of rotation in the knee which feeds down into the ankles and feet.

 

[Zentune]

Your knee joints have rotation. Not a lot but it is there and should be for a healthy knee. It is not just a hinge joint. There is rotation between the femoral condyles and the tibial plateau. And most people are scared to use rotation in their knees even though most people do it without thinking anyway. In fact clinically i see a lot of people post ACL surgery that cant fully extend or flex their knee because the rotation that goes with these movements is missing. But if you want to only ski around with flexion and extension present be my guest. But you're missing a level of control, balance and precision.
Feel free to google literature on rotation of the knee joint. here is a video as an example:
ANd dont forget to test rotation in closed chain motion (foot on the ground) as opposed to open chain (foot in the air) which is what everyone on the forum has suggested to do by sitting down with a flexed hip and knee to test. Its very different and you will find that there is more internal rotation possible when the leg is in closed chain. Plus this is far more applicable given when skiing our legs will be acting more in closed chain type motion!

Just found this thread and wanted to add my two cents worth.

Thanks for the video Tom. I forget, a healthy knee has about 3 or 4 degrees of rotation upon flexion and extension? Do I have that right? It’s the shape of the tibial plateau/femoral condyles that largely determine this ie, they are not totally flat and parallel to on another at the interface....and I would guess that it is set up this way to aid with internal and external leg rotation and pronating/supinating of the foot?

zenny

 

[LiquidFeet]

@tomgellie, I've been looking for confirmation that the knee has legitimate rotation built into its form but couldn't find anything. You just posted it; thanks for that.