I have been doing the Intensity series without a stability ball for awhile now (didn't think I'd need it). I just purchased a ball last week and used it for the first time in PUB and PLB. All I have to say is WOW! The stability ball is my new favorite workout tool and I can't wait for more videos from you incorporating it. For those who do not own one I highly recommend it. They make the exercises so much more intense and effective.