My endeavors in IP/IS lead me to think that continual reduction of muscular effort allows ki to flow more easily and freely (and thus with more power). Reduction of muscular effort draws everything more and more back to the center. I say this because I have found myself consciously changing my impulses from sending effort and preparation into my arms to leaving the arms completely relaxed and free of effort. I think more of using the main body to achieve my intention than of using the arms. So my mind/nerve power/ki don't rush into my arms anymore but stay in my center.
Not to say that there's no extension of the ki into the arms and legs, but it goes there in a different way, now, more like an observer than a commander--not to put my arms on hyper-alert but to make them receptive to very subtle efforts and contacts.