boxing is more modern today! like compare the soccer players of the past and of this era. here you can see the same thing.
This is pretty much it. We know more about conditioning now than we did 50 years ago. If boxers arent in shape now,they're just lazy. There no excuse to not be in amazing shape.
and of course there are boxers of the past who were in very good shape. but today you can see much more of them. also it is normal that you have "fat" boxers in the heavyweight divison!
An also genetics. Some people can just go through the motions an gain muscle. Alot of the guys in the old eras were shredded. you just dont have color pictures an hd to see.
Because Haye does repeat sprints for cardio and isn't afraid of weights. Those other guys were afraid of weights and went for long slow runs every morning.
:deal There is more fat heavyweights today than ever before, and they still talk new era blah blah blah, back then they fought 15 rounds and its not like they run out of gas or anything else, they maybe needed more time to be in perfect condition for fight but they were able to be just as ready as fighters today.