[Weightshift]

The Left Arm (and Club) is what is being 'picked-up' by the Right Forearm. And this lift is accomplished by the bending of the Right Elbow (7-3) and the use of the Right Deltoid to raise the Right Arm. The active muscle in the Arm action is the Biceps. It is the only time during the Stroke that this muscle is actively employed. In the Downstroke, the Biceps are "completely passive" (2-M-3).

To understand this action, simply extend your Left Arm directly in front of you about chest-high. Grasp your Left Wrist with the thumb and forefinger of your Right Hand. Then, using only your Right Arm (no Left Arm activity) proceed to lift and lower the Left Arm to your heart's content. Notice that the Left Arm is completely passive and the 'work' is being done with the bending Right Elbow (via the Biceps) as the Right Deltoid (Shoulder muscle) lifts the Right Arm.

For someone trying this exercise for the first time they will find that even with extensor action applied, the 'passive left arm' tends to bend at the left elbow.

The difference in the golf swing is that there is a pulling action between extensor action and the left shoulder as the body pivot lags the hands, so the left arm is being pulled at both ends, preventing any bending of the left elbow.

The exercise could be modified to include a left elbow locked in place to prevent itself from bending but this would send the wrong message to the brain.

The only differences between this action and your actual Backstroke are (1) you are lifting and lowering in a vertical plane in this drill versus an Inclined Plane in your Golf Stroke and (2) there is no Pivot in the drill and there is in the actual Stroke.

Regarding the Right Hand, Extensor Acton pulls the Clubshaft in-line with the Left Arm, usually during the Start Up. This Flattens the Left Wrist and Bends the Right. This action occurs in tandem with the Right Forearm Takeaway in a true, Three-Dimensional Backstroke (Up, Back and In, simultaneously and On Plane) as the Pivot performs its work (producing the circular motion of the Stroke while maintaing Balance and the stability necessary for a Centered Clubhead Arc).