After doing step for about a decade, I found this one, and was surprised to find it challenged me quite a lot. Karen's choreography and combination of strength and cardio moves meant that I got a much better workout than I had been getting for ten years! After starting her workout, I found my muscle mass increased significantly, I felt fitter and stronger, and my abs/core strengthened a lot. It is by far the best step workout I have ever used, and I have used dozens! The ab section on this DVD is the most difficult I have EVER come across! I have had to stop stepping because of consequent knee problems, but I use many of Karen's other workouts and love them. I'd especially recommend her Half & Half (cardio & weights); Burn & Firm (circuit training); Total Body Training (pilates floor routine with pilates ring); AM/PM Fitness (also in Strong & Streamlined double DVD); Core Plus More (also in Yoga & Sculpting double DVD). These are her very best!