I have been having serious problems with my knee cartilage so I am thinking I should back off of doing impact workouts and focus more on building strength. I have the Slow and Heavy series and I was wondering if anyone could tell me how they do this workout. Do you do each of the 3 videos 2X per week or do you do them 1x per week spaced out with cardio in between? What is the most effective way to build some strength? Any help would be greatly appreciated.