Hello Sharon! If you're having problems with your knees I don't think doing Hi/Lo is going to help you. Most Hi/Lo tapes on the market today are mostly high impact. Very high impact! They include some low impact recovery intervals and low impact warm ups but the rest are high impact moves. I think hi/lo is harder in terms of impact than step because the step cushions most high impact moves that would be awful for your knees when practiced on the floor. I think that if you're trying to reduce or eliminate the impact on your cardio routines you should try to modify the high impact moves when you do step, or do low impact floor or step aerobics instead. Well that being said, I still think hi/lo is great for cross training and you get your heart rate up there all the time. If you still want to try it there's Cathe's MIC Hi/lo section (although I still modify some high impact moves) and Christi Taylor has great hi/lo tapes like Hi/Lo Heaven and Happy Hour Hi/Lo (also very high impact).