Why would training biceps be funner than other groups? You feel more in the legs and the legs are the most practical too as they enhance metabolism and running speed the most but it's good getting a compete workout.
Anyway, the book one isn't a myth per se but rather that people don't study correctly.
http://www.thechessworld.com/learn-chess/18-general-information/332-5-myths-about-getting-better-at-chess-most-players-believe
What do you think chess.com players? Which of the 5 is a myth?