Can Too Much Cardio Kill You?

Are You Running to Death?

As a visitor to, you ARE an exercise enthusiast; you hit the trails in the morning and crush the weights in the gym– or at least you intend to. Some of us become quite addicted to working out and love the endorphin rush that comes with intense exercise. We follow prescribed exercise programs with periodization and even overreach now and then to blast through plateaus. Sometimes that overreaching even becomes overtraining syndrome with fatigue, disordered sleep, weakness and pain. Nevertheless, despite the occasional setback, we work around our injuries, take breaks when we need to and use dietary supplements to recover faster.

Can We Do Too Much Exercise?

We are told that exercise is good for the heart, the brain and the soul. That being said, many studies substantiate the metabolic dysfunction that occurs with a sedentary lifestyle and the shorter life span that goes along with it. Exercise can increase longevity, decrease the risk of diabetes and heart disease, and even alleviate symptoms of depression. With all the benefits that come with exercise, is it even possible that we can do too much? Indeed, research suggests that there may be such a thing as doing too much exercise for our own good. In fact, research suggests that those who we once thought as the fittest of the fit, marathoners, are in fact no less likely to die of heart disease than the average couch potato. Sound a little far-fetched? Let’s look at the whole story.

Marathon Race to the Death

This story starts a long time ago. In 490 B.C., Phidippides, a 40-year-old courier, ran 26 miles from a battle in Marathon to Athens to proclaim that the Greeks had won. Upon uttering his proclamation, he collapsed and died.1. Fast-forward to the 1970s when physicians began proclaiming that if you could run a marathon, you could be impervious to death from coronary artery disease.2 How we as an educated society made the leap from Phidippides’ death after his 26-mile journey to the immortality of marathon runners has always baffled me. Have you ever been to the tent at the finishing line of a marathon? It is a disaster scene; hot, red swollen knees, people collapsing, people carrying bodies, others plainly just passing out. Although the death count at most marathons is up to 1 in 100,000 participants, it is definitely not easy on the body and research suggests that this repeated stress over years exacts a toll.

Side Effects of Extreme Exercise

Chronic, extreme exercise appears to cause structural damage to the heart that may be a sign of repeated insults, injury and scarring. This wear and tear offsets the cardiovascular benefits of moderate exercise. Studies show that even vigorous exercise for up to 40 minutes per day can reduce mortality by almost 40 percent.3 Beyond 45 minutes, no further benefit is conferred by vigorous exercise on the heart, at least statistically. Interestingly, light to moderate activity proportionately lowers mortality risk to times of up to 110 minutes. It can be inferred from the data that those who train with high intensity over long periods of time are interested in something other than their longevity.

Cardio Can Damage the Heart

So what is it about long-lasting, one- to two-hour, vigorous intensity endurance training that causes damage to the heart? When training at high intensities, such as distance running, blood has to be returned to the heart and pumped out at rates up to five to seven times resting levels. As blood returns from the leg veins at this rate, the right ventricle of the heart, which accepts the venous blood, is overstretched. This overstretching is much like doing an extra heavy eccentric biceps curl (the contraction on the way down). If you have tried “eccentrics” in the gym, you understand the damage it causes to the muscle, as the next day you are so sore you can barely comb your hair. Just as markers of muscle damage rise in the blood with eccentric exercise, high-intensity endurance exercise causes an elevation of blood markers for heart muscle damage.4 Although those markers return to normal after about one week, damage to the heart wall has occurred and healed. How often can the heart go through such stress?

Short Bursts of Energy Better

The heart and our metabolic physiology have not evolved as much as technology has in the past 100,000 years. Our Paleolithic ancestors would hunt down their prey with stone tools in short bursts of energy over relatively short distances. They experienced regular bouts of famine, and survival of the fittest prevailed. This led to evolution of human physiology capable of storing fat more easily and conserving energy when hunting. Then comes the cultivation of wheat and carbohydrate energy sources, which become overly abundant. Humans are then able to expend energy over longer bouts of time. However, the environmental pressures to evolve are erased by technology that allowed life expectancy to grow beyond early mating years. In other words, our hearts were designed for short bursts of energy for 30 to 50 minutes, not two to three hours. These high-volume episodes of vigorous activity have been proven to damage the heart’s muscle fibers with microtears, inflammation and scarring.5 Research has demonstrated that heart disease patients treated with 30 or 60 minutes of vigorous exercise sessions better improved arterial stiffness and had less oxidant stress with 30 minutes, versus worsening of both conditions with the 60-minute sessions.6

Recent Cases

The most disturbing research about the detrimental effects of extreme endurance training has been presented in recent literature. Cardiologists evaluated the amount of plaque formation in the hearts of marathoners that had completed at least 25 marathons over 25 years, and what they found was surprising.1 They found that the marathoners had 60 percent more coronary plaque formation than their sedentary counterparts of the same age. In addition, irregular heart rhythms, even life-threatening ones, can be found in aging endurance athletes in the absence of any significant coronary disease.7 It is encouraging, however, that rat models of long-term endurance training and cardiac fibrosis have demonstrated reversibility of the arrhythmias and structural changes in the heart with discontinuation of the intense training.8

Everything in Moderation

The main point of this post is to follow a principle that I like to live by, “Everything in moderation, including moderation.” The medical literature overwhelmingly supports the health benefits of an active lifestyle over living a couch potato life. As long as there are competitions in the world (forever), athletes will try to outperform others. In that context, one must throw moderation out the window and go all out. In doing so, that athlete will inflict stress on their body that they will have to cope with and recover from. If they don’t allow their body to recover, it will lead to injury. Just as one’s muscles get weaker with overtraining with weights, the heart can be overtrained with excessive high-intensity endurance exercise. The science presented here suggests that once you have attained your endurance training goals or competitive success, you should return to moderation and let your heart heal.

To quote a well-known contemporary of Phidippides in ancient Greece, Hippocrates— the father of medicine: “The right amount of nourishment and exercise, not too much, not too little, is the safest way to health.”

Let me put it another way: Don’t run faster to the pearly gates, because you just might win that race.


O’Keefe JH, et al. Potential adverse cardiovascular effects from excessive endurance exercise. Mayo Clinic Proc 2012;87:587-95
2. Bassler TJ. Marathon running and immunity to atherosclerosis. Ann N Y Acad Sci 1977;301:579-92
3. Wen CP, et al. Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study. Lancet 2011;378:1244-53
4. Ector J, et al. Reduced right ventricular ejection fraction in endurance athletes presenting with ventricular arrhythmias: a quantitative angiographic assessment. Eur Heart J 2007;28:345-53
5. La GA, et al. Exercise-induced right ventricular dysfunction and structural remodeling in endurance athletes. Eur Heart J 2012;33:998-1006
6. Michaelides AP, et al. Exercise duration as a determinant of vascular function and antioxidant balance in patients with coronary artery disease. Heart 2011;97:832-7
7. Patil HR, et al. Cardiovascular damage resulting from chronic excessive endurance exercise. Mo Med 2012;109:312-21
8. Benito B, et al. Cardiac arrythmogenic remodeling in a rat model of long-term intensive exercise training. Circulation 2011;123:13-22
9. Autopsy report Micah True;



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Victor R. Prisk, MD

Dr. Victor R. Prisk is a board-certified orthopaedic surgeon and owner and medical director of Prisk Orthopaedics and Wellness, PC. He is actively involved in the care of dancers, gymnasts and weight-training athletes. Dr. Prisk sub-specializes in foot and ankle surgery and brings experience and empathy to his practice. Dr. Prisk is a member of the GNC Medical Advisory Board and creator of the G.A.I.N. Plan. He is a former NCAA All-American, IFBB professional bodybuilder and professional dancer with Bodiography Contemporary Ballet....   Prisk Orthopaedics and Wellness, PC - GNC - G.A.I.N. Plan - Facebook - Twitter

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