I've read articles which say that some people are overweight because they put very little effort into their day to day motions. Instead of bending down to pick something up from the floor, for example, they'll find a way to lean over and pick it up with much smaller movements instead. Instead of walking at a brisk pace, they saunter. And so forth. He looks like one of those guys.
Again, I try to remind myself that he might have some unknown, non-obvious physical ailment. It's kinda hard to think that when watching him move, though. He certainly doesn't appear to be disabled, and he didn't park in either of the gym's disabled parking spots. Who knows?