I think the movement of the chest and stomach is pretty good, I'd tone down the shoulder shrug though (maybe have them pivot back a little, but less vertical action). the static head looks peculiar with such heavy breathing going on, should probably straighten his neck a bit when the chest pumps out (due to the movement of the spine).
the foot on our left looks like it's on a hill, compared to the other foot, which is flat. could use some darker darks to make it pop, and some more lively, less mauve colors would spice it up a bit too (looks kinda monochrome atm). pixel clusters could use some refining, having a more defined light source might help you make those decisions.
