I was actually thinking about this subject today, not so much because I was doing night photography but because I was really pushing the limits of hand holding ability, seeing how low I could go without any of them new fangled stabilized cameras.
I keep thinking back to a scene from The League of Extraordinary Gentlemen. I'm serious. I don't even remember the characters' names, but Sean Connery is on the conning tower of the Nautilus (or maybe he was on the surface of it, I don't remember) when it's on the surface, talking to the American pistol guy, trying to teach him to shoot a rifle. His advice is to take his time, to recognize when the moment is right to shoot. He said "you have all the time in the world".
That keeps coming back to me when I'm trying to push the limits of stability. It's not about forcing my hands and arms to steady, it's about settling down and feeling when the moment is right. A very zen sort of thing, you don't make it happen, you just recognize it when it does.
Obviously this won't work on a dynamic subject.
I still have to see how well I did today. I'm hoping that I did maybe one in four when at 1/300th or slower, when using my 400mm. I should have managed at least one 1/200th, perhaps several total. I'm talking with no bracing whatsoever. With bracing.. well I have to see how well I did there too.
Okay, I found one, 1/125 at 400mm. I'm happy. Hand held, probably no bracing, roughly one in seven good to bad ratio. And actually it was a dynamic, moving target (a wolf at the zoo, finally they're within my lens reach, they're MINE! all MINE!), although it had probably stopped moving at the moment I took the shot.
Also I think I tend to breathe out when taking a shot. Not hard, I think I just breathe out slowly. I say I think I do because I'm not really sure exactly what I do when I'm in the moment.