[Yoda]

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.

Good point, Weightshift. I could have been a bit more precise with regards to the Left Arm, but the question I was answering with the drill focused on Right Arm and Elbow Action and the muscular activity used to motivate them. And that action will be unaffected by a Left Arm that bends a bit.

There is a misconception, however, that Right Arm Extensor Action alone is responsible for the Straight Left Arm. That is not true. There is always a Left Arm Triceps Extensor Action at work as well (12-5-1-#10 and 2-M-3).

So, let's add these two items to the drill's instruction:

1. Straighten -- but do not 'lock' -- the Left Arm with a Left Arm Triceps Extensor Action.

2. Further stretch that Left Arm with a gentle tug of the Right Arm's Triceps Extensor Action. The Right Arm will straighten somewhat, but will remain Bent due to the Checkrein Action (the "leash") of the Left Arm.

My only concern here is that by introducing this new terminology -- Left Triceps Extensor Action -- I am potentially confusing the definition of Right Triceps Extensor Action as the TGM Power Package structural process outlined in 6-B-1-D. However, in my opinion, there is a need to address the Left Triceps role in straightening the Left Elbow, and that is what this term does.