It isn't a stupid question mate and I notice you never got a response............ You could be as scientific as you want with weighing food, how much exercise, finding out what suits your dog the best etc, but that's the problem. Just like you and me, dogs are all different, each having different levels of fitness. Some folk look at a well muscled dog and think, theres a fit dog. To an extent it probably is but a running dog needs stamina and you can't look at a dog and see stamina. Same with humans, most people who have stamina are thin not well built, take your marathon runners compared to y