Is it Hagler? Is it Mayweather Jr.? Is it Duran? Maybe Ken Norton? There must be plenty of others.. how about Greb? Which boxers have particularly impressed you throughout history for always being in tip top shape fight night, and working extremely hard on their craft and fitness?
You gotta give credit where credit is do and Mayweather Jr. really is one of the hardest working boxers I've ever see.
I know that Hagler was always in superb shape and very dedicated to his craft. Mayweather is always in the best shape for his fights, is a gym rat, and so is always in shape regardless of whether he has an upcoming fight or not. I always remember Ken Norton being in truly unbelievable shape and always ready to go.
Floyd works hard and "smart" as he says, meaning that he isn't just dedicated to his physical condition, but mastering his craft, the sweet science, as thoroughly as possible. Nadal is another who has worked insanely hard during his career as a tennis player. Kobe Bryant should also be mentioned for recent times. They can all be respected for their extreme professionalism and hard work for their craft, but I think Floyd might top both of them for this era. Any other suggestions?
No way to know exactly how hard they work as opposed to the next fighter. Hopkins, Mayweather, Holyfield, and Marciano are all known for training extremely hard.
Someone has spent too much time watching documentaries on Hagler/SRL and not enough time actually watching the tape.