Anabolic steroids were not around at that time. Caffeine was about it.
Most of the modern “training” is crap.
Boxers used to fight 45 round fights.
Now they fight 12 round “championship” fights.
Heavyweights Jack Dempsey and Jess Willard (6’6 1/2”) used 5 ounce gloves in their 1919 title fight.
Today lightweights use 10 ounce gloves.