Have been using this video now for about 2 weeks, 2 times a week (interspersed with yoga and weight training). It's still kicking my butt on level 1, although I think that's partially because I am able to do more at the beginning (pushups and squats), but those tire me out for the rest. Anyway, I think it's definitely an effective workout when you only have a short window of time. I may do level two soon even though I haven't "mastered" level 1 yet, just for some variety.