You write-: "I used to turn the shoulders and extend both arms , long and low, with the triangle maintained."
When you state "extend both arms" I think that it correctly describes the mental picture that many golfers have in their mind when they think of the one piece takeaway. However, as Yoda accurately demonstrated in his DVD lesson, the right forearm at address must be held in a certain manner with respect to the left arm, so that the right elbow can start to fold and the right forearm can start to fan (as if performing a right clap hand action) very soon after the right forearm takeaway commences. The main purpose of the takeaway is to simply carry one's hands (and clubshaft) to the "correct" end-backswing position where the left arm flying wedge and right arm flying wedge are correctly aligned (and the entire power package assembly is correctly loaded).
Standing stiffly with extended arms leads to all sorts of incorrect backswing actions - like this frequently performed one piece takeaway action that leads to reverse pivoting.
Threaded Mode
