Make a note: i have arms

I have them, so what happens to them? Why do they sometimes stay so passive as if my blood doesn’t flow all the way to my fingers? There is a difference between a stretched and a loose arm. That’s pretty obvious and i think i know it, so why can’t i also integrate it in my movement? Is there a difference between when i am performing and when i am not? Do i forget these things once i stand in front of an audience or am i just not able to sense the tonus and form of some parts of my body, especially my arms? It’s all a bit frustrating on one hand, on the other hand now i know i (still) have something to work on.