hahahah Why are you working a punching bag?
I`m not trying to be funny. What are you training for?
boxing is a great form of cardio. I find it much more productive than spending an equivalent amount of time on a treadmill or elliptical trainer. Not to mention, working on my striking, and timing/accuracy on the speedbag.
I have a timer that measures 3 minute rounds with 1 minute rest inbetween. i do 10 rounds on the 100 lb bag, and then take a rest for 15-20, drink some protein, and then hit the speedbag for 5 or 6more rounds.
then i work on the speedbag again later before i go to bed.