Cute game! I love the vibe it gives. Reminds me a bit of flash games you'd find on nick.com back in the day. One small issue is that if you stay still on the gym you stop getting stronger. It seems like you need to keep moving the fly around on the gym to actually get stronger. (although maybe that's intentional cuz its like you actually need to work out instead of just sitting around at the gym. It'd probably be worth letting the player know if that's the case.)

Great concept, could definitely play something like this when it's optimised!