I own several of Chris Freytag fitness dvds and this is one of them. Prevention Fitness System: Drop It In 30 is an amazing workout. This 50 minute workout is pure cardio which consist of cardio and cardio interval moves. During both workouts Chris Freytag keeps my heart rate up. I really like Chris Freytag training style, she is encouraging and motivational without being loud and up in your face type trainer. There are days when I prefer a more calm laid back workout that deliver results and this is it. Chris Freytag cueing is always perfect during each and everyone of her workouts. She always do every workout moves with you. Chris Freytag never walks around on her fitness dvds while you do the work. She puts 100% effort into each workout and she sweats right along with you. There are a lot of lunges and squats in this workout. So if you have problem with your knees maybe you can modified that part of the workout to fit your own personal needs. This is a great workout and I personally enjoy working out to it.