A healthy heart contracts in regular intervals, the heart muscles circulate fresh blood, one heart beat at a time. Running stresses the heart's efforts: Impulses shoot through the heart with greater frequency, and increase the rate of the heart’s contraction. An increased volume of blood is pumped with each beat of the heart. The flow of blood through the coronary arteries increases to feed the demands of the straining heart muscle. To handle the overflow, the cardiac muscles grow and expand the heart. As a result, endurance runners have a larger heart and a low resting pulse. Compared to a normal person who has a resting pulse rate of 70 beats per minute, my heart only beats 50-55 times per minute. Enlarged hearts need more oxygen and a higher blood flow, and runners are advised to maintain a regular exercise routine to avoid risks of heart attack.
If we think about it, it makes sense. A vigorous running lifestyle places high demand and stress on our heart muscles, they become bigger and stronger, taking up more room, and consequently our body builds larger heart chambers. These now require a higher amount of oxygen, which is transported to our heart via blood flow. Suddenly we switch to a sedentary lifestyle. Less movement requires less blood circulation, the heart muscles become rigid and less elastic, the heart chambers starved of oxygen and important nutrients. Fatal arrhythmia (medical parlance for heart attack) according to studies involving more than thousand subjects is more likely to follow activities such as sex, snow shoveling, or some return to exercise after a long period of inactivity. The sudden rush of blood flow can be compared to a breaking dam, too much volume reaches the heart muscle which in turn contracts more rapidly, in a weak attempt to control a high pressure sudden flow of blood coming in.
Studies agree that consistency and maintaining physical fitness is more important than intensity: “The life-long runner, with a heart conditioned by decades of regular training, has the best protection from cardiovascular disease. The transient runner, roused from a sedentary lifestyle with the aim of running a marathon, may accomplish an admirable athletic goal and may enjoy substantial health benefits, but does not achieve the same degree of protection from cardiovascular disease as the dedicated runner.”
Benjamin Ebert, M.D., Ph.D., physician.
*Some personal risk factors as family history and age cannot be changed. In the case of Jim Fixx, early medical interventions could have dramatically decreased his risk of a heart attack. He had undiagnosed cardiovascular disease. His father died at a young age from a heart attack.