Cardiovascular Dangers of Long-Term Endurance Exercise
Abstract & Commentary
By Joseph E. Scherger, MD, MPH
Dr. Scherger reports no financial relationships relevant to this field of study.
Synopsis: While regular exercise is beneficial to overall health, repeated long-term endurance exercise — such as marathons, ultramarathons, ironman triathlons, and long-distance bicycle racing — may cause myocardial scarring and increase the risk of serious arrythmias, coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening. The cardiovascular benefits of exercise are only seen in regular workouts of up to 1 hour a day.
Source: O’Keefe JH, et al. Potential adverse cardiovascular effects from excessive endurance exercise. Mayo Clin Proc 2012;87:587-595.
THE BENEFITS OF REGULAR EXERCISE ARE WELL KNOWN. PEOple who exercise regularly have a mean life expectancy that is 7 years longer than those who are physically inactive and have lower rates of disabilities.1,2 Exercise has often been compared with medication, and some have argued that it could be the best medication available for health and longevity. But like any medication, harmful effects may occur from taking too much. There is mounting evidence for such harm from long-term endurance exercise.
A team of authors from several major medical groups and universities reviewed the literature about the potential adverse cardiovascular effects from endurance exercise. They reviewed the mechanisms of harm both acutely and chronically from what they consider excessive endurance exercise. Animal and human studies are reviewed and the results are sobering for any competitive endurance athlete.
Sudden cardiac death (SCD) during endurance exercise gets most of the media attention but remains very rare. There is one SCD per 100,000 participants in a marathon, and this rate has remained stable as the number of participants in America has risen 20-fold in the past 35 years.3-6 There is one SCD per 40,000 participants in triathlons and the increased risk is due to dangers during the swim portion of the event. SCD during extreme exertion for participants younger than age 30 is most commonly related to genetic causes such as hypertrophic cardiomyopathy, anomalous coronary arteries, dilated cardiomyopathy, and congenital long QT syndrome. SCD during events for participants older than age 30 are due to coronary heart disease and myocardial infarction. However, it is the longerterm effects on the cardiovascular system that are the focus of this review rather than SCD during endurance events.
Repeated intense and sustained exercise may cause patchy myocardial fibrosis, particularly in the atria, interventricular septum, and right ventricle, creating a substrate for atrial and ventricular arrhythmias. These effects have been seen in rats forced to run strenuously and continuously for 60 minutes daily for 16 weeks.7 In humans, highly trained endurance athletes develop enlarged left and right ventricular volumes, increased left ventricular wall thickness and cardiac mass, and increased left atrial size.8,9 The cardiac enlargements that develop during prolonged training and competition do not completely regress to normal levels even years after the athlete has retired from competition and heavy exercise training, leaving an at risk condition known as the “athletic heart.”10
Biomarkers of cardiac stress, such as cardiac troponin, creatine kinase MB, and BNP, increase up to 50% during extreme endurance exercise training. These increases may reflect myocardial cell damage that may lead to scarring of the muscle. The structural remodeling in the heart after repeated endurance exercise increases the risk in some athletes for atrial fibrillation, ventricular arrthymias, and ultimately right ventricular dysfunction.
Coronary arteries dilate with exercise, but the dilation seen in marathon runners my lead to increased coronary artery calcification and greater atherosclerotic burden.11
Commentary
I have completed 28 marathons and recently three 50 k (31 mile) ultramarathon trail runs. Like many, I am inspired by the 2009 book Born to Run by Christopher McDougall.12 Needless to say this article and the press it generated caught my attention. This review adds reflection to the recent sudden death of Micah True (Caballo Blanco), the hero in Born to Run, at age 58. The human race may have survived for 2 million years because we could run down our food, yet we probably did not have the longevity we expect today.
As physicians, we should caution our patients about the potential dangers of long-term endurance exercise. Everyone will need to balance their own risks and benefits, and competitive endurance athletes will take their chances for harm similar to football, soccer, and boxing, to name a few potentially dangerous sports. As for me, I am happy to limit my miles per week to 20-25 with most workouts being under 1 hour. Even when I run longer, my pace is slow and the stress seems to be more on the musculoskeletal system than the heart. I am always at a pace that allows for conversation. I love how lean and fit this makes me. My son and I are training for a 50-mile run on Catalina Island in January 2013. I am 62 and hope to be here writing these articles for many years to come!
References
1. Sama S, et al. Med Sci Sports Exerc 1993;25:237-244.
2. Chakravarty EF, et al. Arch Intern Med 2008;168:1638-1646.
3. O’Keefe JH, et al. Lancet 2012;379:799. Author reply 800-801.
4. Lee J, et al. Med Sci Sports Exerc 2012;44:990-994.
5. Redelmeier DA, Greenwals JA. BMJ 2007;335:1275-1277.
6. Kim JH, et al. N Engl J Med 2012;366:130-140.
7. Benito B, et al. Circulation 2011;123:13-22.
8. Pelliccia A, et al. Ann Intern Med 1999;130:23-31.
9. Pelliccia A, et al. J Am Coll Cardiol 2005;46:690-696.
10. Pelliccia A, et al. Circulation 2002;105:944-949.
11. Mohlenkamp S, et al. Eur Heart J 2008;29:1903-1910.
12. McDougall C. Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen. New York, NY: Random House; 2009.
While regular exercise is beneficial to overall health, repeated long-term endurance exercise — such as marathons, ultramarathons, ironman triathlons, and long-distance bicycle racing — may cause myocardial scarring and increase the risk of serious arrythmias, coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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