[Daryl]

Is this an equal opposite deal? So, the left is resisting the upward pull of the right? Does that not introduce unwanted muscular tension in the left arm?

I may have missed the ferry on what you are float loading out there. The beauty of extensor action is the "extension without muscular tension in the left arm" Structure sans the rupture!

Set me straight! Sorry, I tend to be punny in the morning (large doses of caffeine doing their thang!)

Apply extension to the Left Arm. Don’t tighten the left arm muscles. Simply push the Left Hand with enough force to straighten it. The Left Arm will only extend very Slightly if any.

Yes, it is kind of an equal opposite thing. So is Extensor Action.