Tomgellie, thank you for reopening this thread. I had a private discussion with another forum member back in January, and actually felt that I needed to correct some of what I said, but you've taken the discussion to a much higher level. What is your background, please?
The video you posted is very illustrative. You identify the movement as "rotation between the femoral condyles and the tibial plateau." If I understand correctly, the meniscus lies between? Does motion occur at the top surface of the meniscus, at the bottom, or as some mix of the two? All this has implications for those who have incurred knee injuries.
If there were any rotation of the tibia and fibula around each other involved, there would need to be some motion at the ankle joint. Does any such motion whatsoever take place?
Allow me the following observations. In identifying the gross motor movements that take place in skiing, the first thing we are interested in is the rotation that we can achieve of the foot relative to the knee (or specifically relative to the upper leg, the tibia). As well as resulting from what you have called knee rotation (I'll stick with that terminology absent a better term), this results from movement in the subtalar joint. As others have noted, the contribution of subtalar joint motion seems to be much the larger of the two. One can separate the contributions of the two by observing the degree of rotation of the ankle bone protrusions (on the axis of the shin). Try the following after taking off your socks and stripping to shorts (or less, that's up to you). First stand tall, and pick up one foot only slightly from the floor, so that the knee is bent very slightly. Turn the foot left and right, without rotating the upper leg. I think that you will find that you are able to achieve very little knee rotation. Muscular engagement is not sufficient to overcome the resistance of the tissues. Now place the foot on the floor, with the knee still very slightly bent. Keep your balance on a chair back or something with your hands. Now use body rotation to twist the knee. You should be able to achieve some slight rotation. This tells me that with the leg in this position, the function of the knee rotation is probably primarily shock absorbtion, as opposed to active movement. Now, finally, sit in a chair, and raise one foot, with the knee bent at about a 90 degree angle. In this position, I think that you will be able to achieve a SUBSTANTIAL amount of knee rotation.
I think that in part this is what you meant when you said, "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."
To me, this is an illustration of what our trainers have been harping on--that generally speaking, we have greater ranges of motion available to us when all joints are somewhat bent, when muscles are neither fully stretched nor fully flexed.
There are undoubtedly differences in the results from achieving foot rotation mostly from knee rotation as opposed to mostly from motion in the subtalar joint. I see differences in the effects on inversion versus eversion, which will be very important to ski performance. An interesting question to me is, to what degree can we independently control knee rotation and subtalar joint motion? Or does our nervous system input largely treat the two as a single movement?
The video you posted is very illustrative. You identify the movement as "rotation between the femoral condyles and the tibial plateau." If I understand correctly, the meniscus lies between? Does motion occur at the top surface of the meniscus, at the bottom, or as some mix of the two? All this has implications for those who have incurred knee injuries.
If there were any rotation of the tibia and fibula around each other involved, there would need to be some motion at the ankle joint. Does any such motion whatsoever take place?
Allow me the following observations. In identifying the gross motor movements that take place in skiing, the first thing we are interested in is the rotation that we can achieve of the foot relative to the knee (or specifically relative to the upper leg, the tibia). As well as resulting from what you have called knee rotation (I'll stick with that terminology absent a better term), this results from movement in the subtalar joint. As others have noted, the contribution of subtalar joint motion seems to be much the larger of the two. One can separate the contributions of the two by observing the degree of rotation of the ankle bone protrusions (on the axis of the shin). Try the following after taking off your socks and stripping to shorts (or less, that's up to you). First stand tall, and pick up one foot only slightly from the floor, so that the knee is bent very slightly. Turn the foot left and right, without rotating the upper leg. I think that you will find that you are able to achieve very little knee rotation. Muscular engagement is not sufficient to overcome the resistance of the tissues. Now place the foot on the floor, with the knee still very slightly bent. Keep your balance on a chair back or something with your hands. Now use body rotation to twist the knee. You should be able to achieve some slight rotation. This tells me that with the leg in this position, the function of the knee rotation is probably primarily shock absorbtion, as opposed to active movement. Now, finally, sit in a chair, and raise one foot, with the knee bent at about a 90 degree angle. In this position, I think that you will be able to achieve a SUBSTANTIAL amount of knee rotation.
I think that in part this is what you meant when you said, "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."
To me, this is an illustration of what our trainers have been harping on--that generally speaking, we have greater ranges of motion available to us when all joints are somewhat bent, when muscles are neither fully stretched nor fully flexed.
There are undoubtedly differences in the results from achieving foot rotation mostly from knee rotation as opposed to mostly from motion in the subtalar joint. I see differences in the effects on inversion versus eversion, which will be very important to ski performance. An interesting question to me is, to what degree can we independently control knee rotation and subtalar joint motion? Or does our nervous system input largely treat the two as a single movement?
