I tried Johnny's heavy bag workout a couple days ago and let me tell you, it's legit. I started out with a light warm up, then dove right in to the explosive punches followed by the jabs. Johnny recommended two minute intervals but I forgot when I started so I did about three one-minute intervals in the beginning. It was only then that I realized Johnny would have said, "hey GAINZ-maker, it's two minute intervals, guy..." So I stepped my game up and did a few two minute intervals.
To everyone's surprise I'm sure, I'm actually not used to mashing my hands into dense, fleshy objects so I focused more on the speed of my hands than the power of my punches. Also, I wasn't wearing gloves so I didn't want to pull a Corey Maggette and break my hand against something that I thought was softer than it actually was. Are you ready for Maggette? Didn't think so.
I kept the rest periods to a minimum and checked my heartrate as well. I think the highest it reached was around 90-something. Not too high for me, but higher than when I want to go postal on everyone at work...so that was a plus. (Look out for a feature on heartrate monitors in the future.) My chest, arms, back, and, especially, shoulders felt a nice pump during the workout....not the 'saturated' pump feeling that comes with lifting weights, but more of a muscle 'buzz' that was a hyrbid between cardio and the aforementioned ferrum lifting.
Anyway, the actual workout itself wasn't too difficult for me, but I would imagine it'd be difficult for anyone not used to explosive movements. And although I didn't find it overly taxing, I was sure as shit sore in my lats for the next couple of days. No wonder boxers have such coveted V-shaped backs. So give it a college try. I would imagine this workout would integrate easily in any circuit training. I will definitely be sure to incorporate more boxing workouts into my training, not only because of the latisimus dorsi benefits, but also so I'm a little more prepared the next time someone asks me if I "want to throw hands" as I glide into ski lift line. You never know when shit is gonna go down.