I'm athletic but not heavily muscular.  This shirt stretches a little more than I'd like in the chest, making the buttons look pulled.  Unbuttoned all the way over another shirt it looks ok, but I like two buttons fastened.  Overall I am pleased with the look.  If it were shorter I would go for a large, but that would make it much too long on the sleeves and waist.  Maybe some careful dryer shrinkage experimentation is in order. Hmmmm...  Anyway, good quality for the price and good looking shirt, just watch it if you have a developed chest (unless you want the button-popping look).