While I was playing with this yesterday, I found several interesting things I could do. If I took a big breath in while raising my arm, I noticed that the expansion of my chest made my shoulder arms start to raise (because my arm was resting on my ribcage) and if I slowly added shoulder pressure from there, the activation of my deltoid was very subtle, and much harder to notice. However when my arm was extended out 180- I could still feel a hard deltoid holding my arm up.
this is the starting point of the suit model from Sigman using reverse breathing. as i understand it, when your "suit" is well developed, it helps you manage the load on your muscles. Ikeda sensei demonstrated a bit of this http://www.youtube.com/watch?v=4hB-knlRDZ8
you know that ki/chi means air right? that's one of the reason my diet is heavily compose of beans, cabbage (both fresh and highly toxic fermented), and with a touch of cinamon for flavor.