My American pitbull terrier is 1. His name is drizzy.. I juss got him about a week ago.. we go for jogs, and alot of sprints along trails where he has to jump and go under trees and run up some small hills, and through sand.. we also play tug a war.. when I got him they were giving him crap with grain..i switched him to wellness core recently.. it's only been a week but I see sum difference in muscle.. we hit the trails 3 times a day for about half hr each.. I don't think he was gettin anywhere near that before.. Any other tips??