The line between supersets and circuit training is, uh, fuzzy, depending on whose definition you use, but that being said, using a different muscle group for the next set allows shorter rest periods, which translates to more work (that's good) all other things being equal. It also allows heavier weights to be used. As I have gone heavier and worked on shortening rest periods, it gives me some anaerobic conditioning, too, which is helpful as a cop, because confrontations generally don't have warm-ups, pacing, etc. :) Even without (aerobic) cardio, with supersets/circuits and shorter rest periods, myself and my friends think we have gotten better at re-converting glycogen and lactic acid so we can keep going. Hey, maybe we've just learned to ignore the burning, but we think something physical is happening. And yes, dammit, I like donuts with my coffee -- lots of coffee, but only one donut per shift :)