The best way yet discovered to lower the resting heart rate is, paradoxically, to make it beat faster during short periods of exercise. This exertion strengthens the heart so that it performs more efficiently at lower rates. This lowered heart rate is called the "bradycardia" of training.

Marathon runners and other endurance athletes characteristically have low heart or pulse rates. Heart rates below 40 have been recorded in superior athletes. A heart rate below 40 is usually suspected to be a pathological condition caused by a conduction disturbance in which the nerve impulses have difficulty passing through the tissues of the heart. There is the story of one athlete who stunned an examining physician and a consulting cardiologist when they found his pulse rate to be only 34 beats a minute. At first they wouldn't let him exercise. But after careful study of the athlete under laboratory conditions, they decided that an extremely low heart rate was perfectly healthy for him.

The heart is strengthened two ways during exercise, first by improving the quality of the heart muscle, called the myocardiurn, and second by increasing the coordination of the fibers as they wring blood out of the heart during each beat. The heart works something like a wet towel when you wring the water out of it.

To demonstrate the action, put the fingers of the left hand into the palm of the right hand, and squeeze those fingers with the right hand, just as the muscles of the heart squeeze against the blood. If all the fingers squeeze together with the same amount of force, the fingers of your other hand will be tightly compressed. If the fingers squeeze weakly and out of concert, the compression won't be nearly as forceful.

Each squeezing finger represents a group of heart fibers. If they all move in a continuous, rhythmic manner, then each set of fibers has less work to do. The fibers are like athletes: they need training. When they're unused, they're uncoordinated. Some of the fibers become lazy, so others have to work harder and more frequently in order to move the blood around in required quantities. In exercise, you have an increased return of blood from the veins, which gives the heart resistance to beat against. It's the resistance, or loading, that causes the heart to develop.

The heart too needs its "overload" if it is to be conditioned. To achieve this "overload," you must pursue an activity that pushes your heart rate to a level a little higher than you get in everyday routine activities. Your goal is to eventually get your pulse up to 120 and hold it there for a few minutes - every day, if possible. Milder exercise is better than nothing, but not sufficient to increase your heart's vigor.