Was Rocky a Marathoner? This article says yes. According the article, Rocky ran a total 30.61 miles during his famous training runs. Even after this distance, he had enough energy to make it up the stairs of the Philadelphia Art Museum steps.
Running is a great way to boost your cardiovascular system for endurance which no doubt helped Rocky defeat Apollo, Mr. T and the Russian. Plus, who doesn't have Eye of the Tiger or the Gonna Fly on their IPOD for extra motivation when out running.
Watch this Video before you head for a run. See if it helps to motivate you.