Breath along with your animation. When he starts inhaling, inhale along with him. When he freezes, freeze with him. When he exhales, exhale with him. Make sure your timing matches perfectly with his. Doesn't it hurt your chest?
Now breath naturally, and pay close attention to how long each breath takes, how fast you breath, how long you take between breaths, and everything else. Trace the arc of your breath with your finger if it helps. Make a graph in the air with your finger to help with your timing. Steadily move your hand to the right, without changing speed. This represents time. Move your finger up when your exhale, down when you inhale. Break it down slowly.
Act out your animation in front of a mirror. Pretend to be a huge badass who's about to cause some trouble. Hunch over a bit. Flex your muscles. Breath in deeply and calmly, confident that you're going to win your fight. Stare yourself down in the mirror. Breath audibly, like a clay monster. Again, pay attention to the timing of your breath, and to your posture. Live your character, so that you can just copy yourself. Pay attention to what your arms and chest and such are doing. Don't draw again until you've consciously decided what your timing is going to be, and what your character is going to be doing. If you can't decide *what* you want him to do or *how* you want him to do it, drawing isn't going to help you.
Do whatever you need to do to realize the timing of your animation. I'd suggest reading the Animator's Survival Kit, if you haven't already. It'll help you a lot, I think. Fantastic book.
And try to have fun when you draw. You're drawing to learn right now, right? And you're definitely learning, even if it doesn't feel like it. Judging by your artwork, you've already been drawing long enough to know that, though. Keep at it! =)
Edit: Tapping along like a metronome also helps. Breathing in takes on beat, as does breathing out. Then there are two beats of rest. Depending how fast your tap, of course! It could be two beats of of breathing in, two out, then four not breathing at all. Or one beat for the whole breathing segment, then one just resting. The point is, whenever he takes a breath, and then exhales, he waits the same amount of time before taking another breath. Like I said earlier, try breathing along with him like that. If you're out of shape like me, you'll probably become lightheaded, for want of oxygen!
The timing is so important in animation! Right now you have a 1:1:2 ratio going on for inhaling:exhaling:resting. Do your acting, and find the natural ratio! And then speed the whole animation up or down, and see how it works. Good luck!
