I have gone through a few phases in my fitness life, from skinny runner, to bulky rugby player. Now I just try to focus on mobility and a good balance of cardio and strength. I still think I could outrun most people, but don't have any illusions about keeping up with the serious runners, same with the powerlifters. I don't even try to go too heavy on anything anymore, as the joints aren't as reliable as they used to be. I think everyone has a weight and physique that is best suited to them, and if you eat right and stay active, your body will end up as it is supposed to be.