Abstract: Cardiopulmonary interval training between a user high target heart rate and a user low target heart rate is obtained with an exercise apparatus by increasing the load of the exercise apparatus at a first predetermined rate until either the maximum machine load is obtained or the high target heart rate. When this event occurs, the load can then be maintained at a fixed level for a predetermined time. Thereafter, the load is decreased until the low target heart rate is obtained, or the user-set exercise duration expired. The heart rate of the user is monitored during the exercise. In the event that measurement of a valid heart signal is lost at any time, any increase or decrease of the load of the exercise apparatus is terminated until a valid heart rate signal is reacquired. In the case when an exercise apparatus is a treadmill, the load can be varied by increasing or decreasing both the speed adjustment and the elevation adjustment of the treadmill.