because stamina and endurance are two things. walk for 1 hour every day to increase your
endurance. you wont ever wear out your joints and its a basic boxing movement.
you walk when you take guys out for a nice walk around the ring. you dont run. you dont jump. you walk.
and you skip rope for when you skip around the ring.
and you hit a speed bag so your arms dont get heavy. you shadowbox in front of a mirror so you see what they see. you spar to sharpen your timing and spacing. sugar ray robinson only used to spar 3 rounds and only every other day.
rocky marciano walked a lot. he had the endurance to go a hard 15 rounds. most guys today dont. so so much of boxing is preformed at just a walking pace. not a running pace. not a sprinting pace. you can run and you can sprint and you can increase your stamina. but walking is the best way to increase your endurance.