I'm in the middle of the latest edition of P90X. X3 is a condensed version of the originial P90X. The theory being that the most effective part of the workout is the first 30 minutes, and workouts that go for an hour mean that you are likely to pace yourself more and not get the most from it. Where as if you know it's only 30 minutes you will have more of a tendency to push harder. I'm down 15 pounds already.