What the hell are you talking about? Look at Micheal Phelps, the guy is in PERFECT shape, he can swim for miles, run for miles, his lifts are actually pretty good from what I heard from a friend who used to swim with him... The guy easily works 4-8 hours a day, and like what Elipse said, he eats like a horse, if he is really taking in enough calories and getting enough sleep then he can still grow, I'm starting to see better visiual gains in my body now that Ive incorporated more cardio, and suprisingly I think my lifts are feeling better too. I'm sure there is a point where it will effect your muscle gain, but many pro atheletes train many times a day, obviously he isn't trying to be a body builder, but you look at the Wide outs and Cornerbacks in the NFL, those guys are about 5'10-6'2 180-220 almost pure muscle, they have large arms, decent sized legs and core, and cut too the T. They also do endurance cardio, HIIT (way beyond what any BB would do), and lift pretty much every day.