It seems to me that different people have knee problems that are aggravated by different things. FOr me, it's not so much impact as torquey moves (that have you turn at an angle) and/or moves done at a faster speed, that may not allow the foot to get into perfect postion. If your knee problems are aggravated by speed and torque rather than impact, then many of Cathe's more recent step tapes may cause you problems, IMHO. If it's impact, then you can always modify to lower impact. Some moves, like 16 hops on the same foot, seem inherently risky for people who have knee problems of any kind. Just too much impact on one leg for too long a time. When I did IMAX2, I modified those by doing an "air jump rope" move switching between legs. If you want to try the new workouts and see if they work for you, you might want to try the IMAX2/C & W DVD. C & W choreography seemed less torquey to me. The step cardio in the terminator is mainly from these two workouts.