[lagster]

hcw said..." I think that if you have lots of tension in the muscles of the arms, then you can use them very well to swing"

I think what you are saying could work, but probably better for a Hitter.
6-B-1-D-- Extensor Action-- "This stretches but does not move the Left Arm"

I heard Extensor Action once described as... "extension without tension"

There are probably also different TYPES of tension. A feeling of being athletic, confident, and ready to produce a dynamic stroke, is different than tension that is induced through anxiety, apprehension, nervousness, or poor technique or concepts.

When you get that confident, athletic, FEELING, and are producing quality shots, then you are on to something. This probably feels a little different for everyone.