I was doing circuits in the past two or three weeks or so, most of the time doing both upper and lower body segments in a row -- no days off in between. I was using medium to light weights and was never sore after the workouts.
I just simply wanted to do something different, and honestly, I love circuit workouts. (Terminator, SS, BC, PP, HSTA, SJP etc.,)
Result? I'm very toned. No new muscle building, but whatever I have seems to be firmer than before. I suspect also some body fat loss.
I don't think I would want do this circuit thing all the time, but it was fun for a few weeks. Probably I'll do S&H next week, working on only one bodypart a day, just for doing something totally different again.
My body did not suffered from this everyday circuit type workouts, but I think it is a very good idea to mix this type of training with some traditional weight lifting.
Mari