Re: Exercice to develop sense of center
I agree with you on the problems with the term "relax" but if you use "muscular power" the way you propose nobody else in the universe is going to understand you.
Furthermore, everybody who talks about this stuff talks about getting away from muscular power--the quality of movement you are looking for does not feel like using muscles, it feels like dropping muscular force, like you're not doing anything with your muscles.
The tai chi people talk about "softening" the joints instead of relaxing. I find that a useful image--if the joint is soft, it's pliable and flexible--probably not tense or rigid. And I can always work on getting it softer.