Surprisingly, I actually liked the keybinds. I would though always get confused with the muscle change menu. Maybe instead of pressing Q and then having to navigate with A and D, you could just press Q once to open the menu, and then cycle the menu by pressing Q again and again. Just an idea though.
Besides that, the game was fun! I liked the artstyle (Although the first muscle guy doesn't have any animations, is that supposed to be like that?). But I honestly didn't understand what the ability of the first muscle is. xD But it didn't really get used I think?
You could've also tried to integrate the enemies a bit more, they were present in just one level.
The tutorial with the doors was also really neat! As far as I can tell, one could only advance to the next door using the knowledge learned in the previous door. That's a great idea.