Originally Posted by ssh
Si, let me say that I believe that you believe what you're saying here. Really. However, my training and analysis disagrees with your observation. I have the Phantom Move in Bumps and Rocca clips playing next to each other on my second screen as I type this. In both clips I see the femurs rotating beyond the position of the upper body in both directions, implying that they are actively turned beyond the counter force created by the body separation.
In the case of the bumps, there is substantially more snow spray at the bottom of the turn, implying that the tails break loose and push the snow. In Rocca's case, he turns the skis 90 degrees in the air by rotating his legs (as his knees are pointed directly at the camera. You can see the femurs rotate very clearly). Whether he rotates like that to tip the skis or to pivot them is immaterial. The result is that he both tips and pivots them simultaneously. To claim that he only intended to tip them is clearly inaccurate, since tipping them only would have kept him moving across the hill instead of down the hill around the next gate.
In short, I believe that I see the movements that are described as "rotary for the purpose of tipping." I just do not agree that they are only tipping. Instead, I see them as rotary movements that aid the redirection of the skis and the shaping of the turn.
Steve, I really think we're off track talking about someone making a turn in the air. I guess I'll restate what I'm trying to get across one more time and give it a rest. This is my viewpoint only and not a representation of PMTS (although it is certainly influenced by what I know of both PMTS and ATS).
People here talk about the three things you can do to a ski: pressure, edging, and rotary. (While I think pressure and rotary are both ineffective terms and can be counterproductive I'll leave that for another time). From here I take a definition of rotary in terms of the force and/or torques one applies to the ski through the boot/binding interface. I try to differnetiate any other discussion of "rotary" as one dealing with body positions and movements (although many posts don't allow for this as they employ a vague concept of "rotary").
In theory it would be very simple to measure "rotary" torque applied to a ski by placing pressure sensors on the inside and outside of both the forefoot and the heel of the foot. (Alternatively we coul place the pressure sensors on each side of the binding toe and heel piece). If, for example, we measure an increased pressure on the outside of the forefoot and inside of the heel we know there is a net rotary torque being applied to the ski. Of course given this point of view perhaps it might be better to talk about "significant" rotary torque applied to a ski as it would probably be the rare case where there wasn't some slight differential in pressure gradient (as measured from some established neutral) on opposite sides between fore and aft of the foot.
If you want to talk about hip rotation (as you've done here) then I would suggest you need to invovle a complete description/analysis of the kinetic chain that gives the net effect in terms of action ON THE SKI. As I've said, you can have lot's of hip rotation without imparting any net rotary torque on the ski - just lift and tip your foot without rotating it to see a demonstration. I just don't see or understand the importance so many people seem to place on active and passive hip rotation or movevment around any particular joint. What's important from my point of view is what the net effect on the ski is. Typically, what I do at any joint is pretty much automatically accomplished based on my overall goal, i.e., tip the ski, rotate the ski, retract the ski, etc. Certainly in working on my skiing I may occasionally focus on specific movement about a single joint to try and improve or correct the kinetic chain, but in general it is not a point of focus as it rarely a single joint issue that needs to be addressed. I think one of the best things about PMTS is that it focuses on the most basic movement patterns (with appropriate cues for proper initiation and sequencing) without trying breaking things down in a conterproductive fashion.
Ok so now onto the sequence of Harald in bumps as an example. This is clearly not a very good example to talk about as we don't see a continuous sequence but only a few slices in time. I think this can be VERY misleading but nevertheless, let's discuss it. I do agree with you that at first glance the clip looks to me like there is some active rotary torque applied to the skis. However, as I think about it further and realize that I am only seeing a few snapshots of the skis and not what happens inbetween I start to think that this impression may arise from not seeing the full action of the skis on the snow. Additionally I don't think that spraying snow is necessarily an indicator of substantial rotary torque applied to the ski or the tail slipping out. I can certainly spray snow without applying any rotary torque to a ski. I can also differentially spray more snow from my tail than my tip, especially in bumps where there may be variable deposits of soft snow. Finally I need to admit that I have skied with Harlald a few times in a variety of terrain. From my observations his skiing clearly has very little active rotary and so this probably biases my assessment in terms of filling in the missing gaps in this sequence of time slices. In this regard real life observation of his bump (or other skiing) does not closely resemble the representation of this sequence of time slices.