First off, that dog isn't a "pit bull" nor is he any of the pit bull breeds. At best he's a "pit bull" x mastiff mix (my money is on a Dogue de Bordeaux cross which is as common as pennies on the ground when it comes to large red/red nose dogs).
Although many APBTs are muscular by genetics, the fact that this is a mixed breed dog looking like that makes me suspicious. Creatine is used a lot in dogs.