Nope, separation doesn't just happen, what I'm saying assuming the skier has good tipping technique with the feet, counter balance, pole plants, looking ahead to the next turn assist and facilitate IMO upper lower body separation. You don't start a new turn by turning the head..for me it's the pole touch and tipping that start the new turn, turning the head keeps me skiing in the future....I want to ski where I'm going not where I've been. You know that better than many skiing the tight tree lines you guys ski.
There's no twisting of the legs in my description Max....the moves I described are subtle and occur with strong tipping, counter movements and well timed and connected pole touches or plants.
I do agree with Max in that the pelvis is part of the upper body and should move with it.....many skiers I've been been around and see are too locked in and have a difficult time finding that ability to separate.
Nice Bush on the 10 hours a week Yoga...I too get my gym time....I do think that this all helps in strengthening the muscles that support counter movements and help get that feeling of separation...applyi ng that to skiing is where many have difficulty.
Max, your original question was how do Great PMTS skiers achieve that...
All I know at this moment in time is that good poles, foot tipping skills and counter work create the basis for upper/lower body separation...this rest to me, is about finding the rhythm.
G