Well in Rocky 2, Rocky went for a 30.6 mile run in one scene. Somebody pieced together all the parts to the montage and tracked the distance and did a blogpost on it.
http://www.phillymag.com/news/2013/09/18/rocky-training-run-rocky-ii/
"I enjoy how he actually sprints away from his Pied Piper-like following at the end of this run, making sure they know that he's the professional athlete here and not them. And look how much energy he has left after his monster run!
Top boxers usually do a lot of roadwork to increase stamina; the LetsRun forum says Kelly Pavlik once won an award in a 10K the week of a fight. Ali ran about three miles every workout, per Norman Mailer's book. An episode of 24/7 showed Floyd Mayweather running an 8-miler. But this? This is ridiculous.
Total distance traveled: 2.45 miles this leg, 30.61 miles total
Over 30 and a half miles. Rocky almost did a 50K. No wonder he won the rematch against Apollo!"