I rented this from the library before purchasing it to see if it was for me. I only have about 25 pounds to lose and have arthritis, especially in my knees. I understand the concept of interval training and for this purpose, it is really good. I was annoyed though, that the person on the back right, Lisa, was suppose to be the "modifier" for those who are not able to do the workout so easily at first. Most DVD's (like Leslie Sansone), the modifier person, really does tone the moves down. I found that throughout the dvd, she did the work out at full-tilt, almost more intense than the instructor/lead. At one point, they had these side lunges with the knees and she was doing them full spread and deep (impossible for me). The only thing modified was that she did not move her arms. The arms for most people are not the problem! I think I will stick with my Leslie Sansone dvd's and save my money.