Batman works out every night, all night. He even does some exercises (lifting, toning, that kind of thing) during the day while the rest of us are putting hours in at the office, one of the many advantages of being a billionaire. All that working out makes him incredibly physically fit, and in our working world it's difficult to match his routine. We can't all moonlight as crime fighters, you know? At least there's this Batman muscle costume to help you look like you spend all your time sparring with bad guys and that sort of thing. All the superhero muscles, without all the superhero hassle!