Originally Posted by janitor
It is actually a very good question.
The answer is that they came from a different place, and were going to a different place.
A fighter back then likely came into boxing malnourished, while a modern boxer likely comes in needing to cut some excess body fat.
A fighter back then focused on stamina training primarily, while a modern fighter takes a more multi faceted training programme.
Yeah boxers back then only did exercises that would be beneficial to a boxer. Running, sparring, skipping, speed and heavy bag plus push ups, sit ups, wrist and neck exercises was basically all that was done, because that was all that was needed. Additional exercises like swimming, rowing and axe training all had benefits to a boxer compared to something like bicep curl which has no benefits beyond aesthetics.