I have only been through the instructional Basics, and the Bum Bum videos so far. In my opinion, fully completing the Bum Bum work out would require the knees of a ten year old.No one with weak/problematic knees or backs should invest in this program.The exercises are well are targeted though, with the triangle scultping. The standing exercises just demand far too much from my knees.Classical pilates uses the same principles of working all the muscles (ncluding smaller supportive muscles), from different angles; and it is much safer as it promotes muscle, joint and bone stability versus fights it. For the amount of pilates BBL draws on, you'd be better off just doing pilates.