I think what separated him from the most of boxers of that time was his mental toughness. He was just a pure badass. his training was not so different then the boxers of that time.
The text in bold is simply inaccurate/nonsense. How the hell can anyone sprint 6-8 miles :yep Sprint do build up the body but certainly not endurance in comparison to a slow/fast steady interval type 4-5 mile run. I dont have the magazine article in front of me but until he beat Minter, Hagler used to work on a building site for the petronellis and i have a full listing of his training schedule from the pre title days of his training regime. Off the top of my head i recall he did his run at 6.00am than had breakfast than went into the gym for groundwork and bags before work at 9.00am. He than worked till 5. had rest and dinner and returned to the gym at 7 where he did sparring etc till 9 and he than went to bed at 11pm.
There was a serious bad side about this loneliness - he was apparently very open in conversations after someone would make him think that he is "friendly". This is what Ray did lurking Hagler into fighting with him being non-friendly at all. Also, as the story goes, his loneliness paid bad service to his marriage life later on.
dempsey use to do interval running..he would jog slow..than sprint for 100 meters....than jog to regain....rather than just running at set faster pace or just sprinting... maybe that is what hagler did? :huh