Tony Horton motivates you to the extreme in order to keep you pushing yourself further than you would if you were doing these exercises on your own. He always has the right thing to say to keep you motivated. You will find it easier to get your groove on and push yourself further when you can see Tony and his team pushing themselves to their ultimate limits.
Often times a workout regime will get to be monotonous and the person might get bored with doing the same workout all the time. When you use the P90X series, the trainers make you change your regime in order to work out new muscle groups and let the others heal. This is the key to seeing fast results. If you use different muscle groups for every workout, cross-train, then clothes fit differently faster.
Tony Hortons system runs you through a quagmire of exercises that challenge you to your extreme limits. There are many different types of exercise videos on the market today, but the P90X Shoulders and Arms and other DVDs are by far the greatest system to see results.