4) Add strength and flexibility training. Aerobic exercise isn't enough. You need to train your muscles and increase flexibility as well. This means weight training or calisthenics, such as push-ups, pull-ups and sit-ups. When using weights, concentrate on the main muscle groups-legs, back, shoulders, arms, chest and stomach. Don't lose sight, however, of the fact that the most important muscle in your body is your heart. It is best strengthened through aerobic exercise. And don't forget to stretch all the main muscle groups before and after exercising or weight training.