The majority of my interval workouts consist of heavy bag training and I think it is an exceptional form of conditioning/fat loss.
I typically do either a traditional boxing round, which is 3 minutes of work followed by 30-60 seconds of rest or I will do what is known as punch-out drills; straight punching only (jab and straight rear) for 30 seconds work/60 seconds rest.For the punch-outs, you go at sprint pace for the duration of the work period, punching as hard and as fast as you can.If you can do 10 of those at max pace, then you are in damn good shape.