heart

Sustained Elevated Cardiac Output Can 'Tear Apart' Your Heart Tissue

As you can see from the above studies, the research is converging around the considerable risks that high endurance cardio-type exercises pose for your heart. When you engage in this type of training, your heart doesn't have much say in the matter, as it simply responds to biochemical signals from your body to ramp up cardiac output in order to keep up with your level of exertion. You can’t feel its pain until very late in the game, and at that point, it may be a life-threatening situation.

Extreme exercise causes your heart to massively increase cardiac output, which it may have to sustain for several hours, depending on the duration and intensity of your activity.

Your heart pumps about five quarts of blood per minute when you’re sitting. But when you’re running, it goes up to 25 to 30 quarts, and it wasn't designed to do this for hours on end, day after day. It enters a state of volume overload that stretches the walls of your heart muscle, literally breaking fibers apart.

The problem is, many endurance athletes don’t allow their bodies to fully recover between sessions. They often live in a perpetual post-workout state, which basically resembles chronic oxidative stress. Repeated damage to the heart muscle increases inflammation, which leads to increased plaque formation, because plaque is your body’s way of bandaging the lining of your inflamed arteries.

Over time, as more damage is inflicted, the heart enlarges hypertrophy, and forms scars cardiac fibrosis. MRIs of long-time marathoners reveal abundant scarring all over their hearts. Scientists have also measured elevated cardiac enzyme levels after extreme exercise just like after a heart attack, which can only mean one thing: this type of exercise is damaging people’s hearts.

. According to a study presented at the Canadian Cardiovascular Congress 2010 in Montreal, regular exercise reduces cardiovascular risk by a factor of two or three, but the extended vigorous exercise performed during a marathon raises your cardiac risk seven-fold!

2. In a 2011 study published in the Journal of Applied Physiology, researchers recruited a group of extremely fit older men, all members of the 100 Marathon club (having completed a minimum of 100 marathons). Half of the men showed heart muscle scarring as a result of their endurance running—specifically, the half who had trained the longest and hardest. If running marathons provided cardiovascular benefit, this group would have had the healthiest hearts!3

3. A 2011 rat study published in the journal Circulation was designed to mimic the strenuous daily exercise load of serious marathoners over the course of 10 years. All the rats had normal, healthy hearts at the outset of the study, but by the end, most of them had developed "diffuse scarring and some structural changes, similar to the changes seen in the human endurance athletes."4

4. A 2012 study in the European Heart Journal found that long-term endurance athletes suffer from diminished function of the right ventricle of the heart and increased cardiac enzymes (markers for heart injury) after endurance racing, which may activate platelet formation and clotting. Twelve percent of the athletes had detectable scar tissue on their heart muscle one week post-race.5

5. A 2010 study presented by the American College of Cardiology showed that endurance runners have more calcified plaque in their arteries (which also increases stroke and dementia risk) than those who are not endurance athletes.6

6. A 2011 German study revealed a very high incidence of carotid and peripheral atherosclerosis among male marathon runners.7

7. A 2006 study screened 60 non-elite participants of the 2004 and 2005 Boston Marathons, using echocardiography and serum biomarkers. Researchers found decreased right ventricular systolic function in the runners, caused by an increase in inflammation and a decrease in blood flow.8

8. Research by Dr. Arthur Siegel, director of Internal Medicine at Harvard's McLean Hospital, also found that long-distance running leads to high levels of inflammation that may trigger cardiac events.9