[Jeff]

Here is a simple experiment that supports my opinion that all movements of the left upper limb are passive in a golf swing.

In Yoda's Alignment Golf DVD he demonstrates an extensor action drill where he grabs the left wrist with the his right hand with the right palm facing the ventral surface of the left wrist, and facing the target at address. Now, perform a backswing motion from that address position using the typical right forearm takeaway motion while allowing your shoulders to rotate about 90 degrees and your pelvis about 45 degrees. Aim to get your hands somewhere near the right shoulder, or just behind the right shoulder.

Note that your watch on your left wrist ends up facing the sky at the end-backswing, which means that there must have been internal rotation of the left humerus at the left shoulder socket joint and some left arm pronatory movement at the level of the left forearm. However, all of this left arm's movement was "passive" because the right hand carried the left wrist to the end-backswing position.

Now let the process reverse naturally. When the process reverses - by simply moving your right hand back to where it started with the right palm facing the target - you will note that the left humerus automatically/passively undergoes internal rotation at the level of the left shoulder socket and the left forearm automatically/passively supinates. In other words, as long as the right hand "guides" the movement of the left upper limb, there is no need for any active left upper limb movements in the downswing to cause the back of the left hand to face the target at impact. As long as the right forearm paddlewheels into impact on-plane, the back of the left hand will end up facing the target at impact. It doesn't require any "active" left upper limb action.

One can take this lesson further - continue to rotate your torso so that you face the target at the finish, with your right palm parallel to the ball-target line. Make sure that you allow your right shoulder to keep moving so that you do not "run-out-of-right-arm" and make sure that your right arm is fully straight post-impact thus ensuring that continuous extensor action is present. Note that the back of your left hand will have undergone a 180 degree rotation between the third parallel and the fourth parallel position - and that no "active" left arm actions are required to produce this 180 degrees of rotation of the left hand. One simply has to allow the left humerus to automatically/passively rotate in the left shoulder socket joint while the left shoulder socket moves around to the left and back (towards the tush line).

Jeff.