I think the animation is lovely, the idea communicates clearly and it's a funny idea. Nice drawings too.
However, the timing seems to be very even. Each beat (stretch up & grow muscles, bent down, strain to pick up, fall down) seems to be spaced along the same intervals, making the whole thing a bit monotonous. I would break that up by having the character more actively moving before he grows, maybe rubbing his hands before hulking out, and stretching out the strain before he shrinks again much more to really feel the effort and the weight of the anvil.
Also, it feels like you're going pose-pose-pose-pose rather mechanically, although the movement in between is lovely. The moment just before the lift could do with some more anticipation, such as pronouncedly lowering the rear, to break that action up a bit more.
That said, seven hours seems like a short time to make such a lovely shot. Wow. I'm such a slowpoke myself XD