Let the Big Dog Eat
 

How about a big dog leashed to a pole. The dog can run in a circle on a taut leash arround the pole (your left Shoulder).

The inclined Plane of the RIGHT Arm. It has to be in order to pull inline with the off plane Left Arm.

Too much extensor action
 

Could I have a tension in my left arm and shoulder?

You want your left arm to be as lifeless as piece of rope. The left arm changes conditions (to becoming taught, or straight) because of extensor action which is produced by action of the right hand. Left arm being or becoming straight is not a function of the left arm (rather a fuction of extensor action).

You can keep the left arm straight without extensor action-and I would not call it an action of the right hand-more right triceps .However I'm not splitting hairs -extensor action is important BUT some people already have it -and don't know it:)

I agree. One also needs to mention on plane movement (#3 tracing) and law of the triangle when talking about "left arm straight". Also agree about the triceps.