I have core secrets and I have used it several times. I like it because it is short (25 minutes) but works everything, He will alternate core inbetween working shoulders but he also states that you are still working the core since you are on the ball. I did it this morning and still can feel it in my glutes and lower back. and my shoulders. I want to look online to see if he has anymore, I only have three of the DVD's I think there is another one I don't have.