To me, it looks like he's more in a semi-fighting stance, than breathing.
I guess he is moving too much up and down to breath. Perhaps just animate the torso more, and the legs and arms less?
If you take the time to notice, while just breathing, only head and torso moves (that's me, anyway). I guess it's more a horizontal movement than a vertical one xD With his chest inflating and all.
Sorry If I sound confusing ._.