If you search Google for Plateauing Workouts, you will find a plethora of information on weight-lifting and how to prevent this phenomena. However, the same is true for cardio workouts. Doing the same cardio workout over and over again may seem comfortable but results will inevitably plateau. In order to keep your progress going, you are going to have to change up your workouts. Instead of the same 20 minute treadmill workout, try intervals. Go for 2 minutes, as fast as you can on the Jacobs Ladder and then rest. Let your heart rate come down and then repeat. Try different machines to develop different muscle groups. Mix in intervals with endurance workouts. Switching your workout up will help to keep you motivated, keep your progress going and it keeps your workouts interesting.