Weight training and genetics...
although true that genetics plays a big roll, most well cut and developed bodies are made in the weight training room, backed up by a good diet. You can develop some definition and muscle by just running or bicycling...up to a very limited point, but real athletes need to still supplement their training with weight work outs to develop that extra edge and push (explosive power) in the competitions.
I'm used to be a competitive runner in my twenties, ran a New York '95, participated in a small time triathlon, just to finish, which I did.
You want a sport to make you a real man, train for the Hawai Ironman Triathlon...and finish it!
Another real challenge, where the your whole strenght and endurance is put to the test, summit a Mountain, like I did back in Peru, Huascaran 21,800 ft, pure thin air...anybody have lungs outhere?
Corsaire boarding party....AWAY!