|What do you think about us adding a #6
A rotary movement, regardless of it's intent, is still a rotary movement. Let's not confuse the various combinations of specific muscles and movements that can be used to turn the foot with the underlying physical principles--that I described above.
It is certainly true that tipping a foot involves rotation of the femur, as does turning the leg--it creates torque ("rotary force"). Just because you didn't MEAN to turn it, though, doesn't change the important outcome--a rotary movement by any other name is still a rotary movement! And for every action, there is an equal and opposite reaction--for every torque, an equal and opposite torque. Something has to move the other way, or provide resistance to allow the movement. This point is not debatable, by the way--you either understand it or you don't.
As far as rotary mechanisms are concerned, turning the foot as an indirect result of a focus on tipping it is no different from turning it as a result of directly focusing on turning it. Physics is unconcerned with your intent! Both involve torque, and both entail an equal and opposite reaction. Somewhere.
The question is--where is the equal and opposite reaction? When both feet are planted on the earth and separated, the other foot provides the resistance to the turning of the one. The earth itself "experiences" the equal and opposite reaction.
Lift the "free foot" and the equal and opposite reaction must occur somewhere in the body. Yes, you could swing the lifted foot forward and back to provide a brief impulse, either in the "one-two" action of "rotation," described above. Or you could swing it forward and back quickly, turning the other foot via "counter-rotation." True, these don't involve the "upper body," but they are the exact same principles I described above, and they involve all of their negative side-effects--notably, skidding. And even though you COULD do them, I'm not aware of anyone who suggests that you SHOULD turn a ski by lifting a foot and swinging it forward and back!
Another fallacy seems to be creeping in here. The upper body is much heavier than that little foot and ski you're trying to turn. Especially with the arms extended wide, it carries a lot of rotational inertia. This means that you when you turn your foot with counter-rotation, the upper body doesn't have to move much to provide the "equal and opposite reaction." The countering movement may be almost imperceptible, especially on the simulated and low-friction example of the barstool or lazy susan. But that does not mean it isn't involved! The earth does experience some opposite rotation too, when you turn against it, but it is so massive that you certainly wouldn't notice it.
So no--there is no sixth principle. If you turn your femur and leg--either directly by, well, turning it, or indirectly, as a result of tipping your foot--it REQUIRES a countering force. That force/counter-rotation occurs either in some other part of your body, or it can be transferred to the Earth through the other leg (or a pole, as I also described above).
The fact that there is some incidental rotation of the femur when you try to tip your foot is a poor excuse for suggesting that we should not actively, intentionally, and precisely steer! Indeed, it is more likely to be a problem, resulting in unintentional pivoting of the inside foot when intending to just tip it! It's like saying "my car is out of alignment--pulls to the right--so I don't have to steer...." I've seen many skiers who could not perform "railroad track turns" for this very reason. Purely tipping the ski to its "little toe edge," WITHOUT introducing torque parallel to the snow (pivoting it), involves rotating the lower leg and foot INWARD to counteract the outward rotation of the femur. Coordinating this movement is not easy for some skiers!
Incidental rotation of the femur when tipping the foot is also the cause of many skiers' tails washing out when they try to tip their outside skis more--the notorious "abstem" at the end of the turn.
Anyway, no--there is no #6!
Bob Barnes[ January 17, 2003, 10:08 PM: Message edited by: Bob Barnes/Colorado ]