On Fitness Fix Intermediate, hard to say exactly but I love using it at least once a week to keep my knees in good shape. It literally has all the exercises (or close enough variations) prescribed by my physical therapist earlier this year when my right knee started to feel tweaky again (I have a history of patellofemoral syndrome). I sometimes have a bit of discomfort while doing the routine but that just reminds me I need to engage the right muscles and to be more consistent in doing the routine
I love it and will never part with it, even got a second copy as back-up and I should record the audio someday as further back-up (since I know the moves by heart... I just need audio cues). It's kinda relaxing and hard all at the same time -- Denise Beatty is really good!