Running is the meat 'n potatoes of cardio work, but not the only thing. Jump rope is probably "#2" as in its not exactly as important but still done alongside w/ roadwork. I can jump rope a long time w/o getting tired, it's nothing compared to running 5-6 miles. Bag work and sparring can do alot for cardio as well, if u throw lots of punches that is.
well... yeah, running is the bread and butter of boxing's cardio but it's not the only one. there's also skipping rope, punch mitts, sparring, etc. basically the whole training session is one huge ass cardiovascular workout.
In my experience, doing rounds on the heavy bag is one of the best ways for cardio. By rounds, I mean basically non-stop sparring on the bag, including footwork, moving in and out, and lots and lots and lots of combos. I don't mean throw a punch, stop the bag from moving, reset, wipe some sweat, throw another punch which is how I have seen some people "train" the heavy bag. Also, I've had to do a lot of swimming while I am in rehab, and this seems to be good at building cardio as well. Unfortunately, I am not fully healed so I cannot return to training yet to see exactly how much it helps, but others have told me it will help a lot, so thats another idea.
all parts of a boxing workout tax the cardiovascular system. run, skip rope, work the heavybag, the other bags, mits, shadowbox, spar, footwork. pick what ever you want.
