Regular exercise prevents and lessens the severity of many common chronic diseases and improves cardiovascular (CV) health. If 30 to 60 minutes of daily exercise is recommended for health by the American College of Sports Medicine (ACSM), shouldn’t training three or four hours a day for that marathon or multisport event be even more beneficial? Recent research suggests otherwise. It concludes, in fact, that long-term excessive endurance exercise induces pathologic and potentially fatal structural remodeling of the heart and large arteries in some individuals.
Although it has been recognized that elite-level athletes often develop abnormal electrocardiograms and atrial and ventricular entropy, these adaptations weren’t previously believed to predispose athletes to serious arrhythmias or sudden cardiac death. Recent studies indicate that excessive exercise can lead to rhythm abnormalities. Endurance sports, including professional cycling, have been associated with up to a fivefold increase in the prevalence of atrial fibrillation, according to a 2012 Mayo Clinic report.
Legendary ultramarathoner, Micah True, died during a routine 12-mile training run on March 27, 2012. In the years leading up to his death, True often ran up to 100 miles a day. An autopsy showed his heart was enlarged and scarred and that he died of a lethal arrhythmia. Doctors speculate that chronic excessive endurance exercise may have caused pathologic changes in the heart of this 58-year-old veteran extreme endurance athlete.
Two recent studies published simultaneously in the online journal Heart indicate a reverse J-shaped curve for the health benefits of exercise, showing that, while there is a “sweet spot” somewhere in the middle, too much can potentially be just as dangerous as not enough.
Researchers in Heidelberg, Germany, found in a 10-year study of 1,038 subjects with stable coronary heart disease (CHD) that too much high-intensity exercise increases the risk of death from heart attack or stroke, citing “evidence of increased cardiovascular mortality in patients with daily strenuous physical activity.”
A Swedish study found similar results in a male population tracked over an average 12-year period; men who exercised intensively for more than five hours a week were 19% more likely to develop atrial fibrillation by the age of 60 than those who did so for less than an hour a week. Further, if the men engaged in strenuous exercise often at the age of 30 but almost none by age 60, the risk increased to 49%.
The 2012 Mayo Clinic Proceedings state, “Chronic training for and competing in extreme endurance events, such as marathons, ultramarathons [running events longer than 26 miles], Ironman distance triathlons, and very long distance bicycle races, can cause transient acute volume overload of the atria and right ventricle, with transient reductions in right ventricular ejection fraction and elevations of cardiac biomarkers… .”
The heart changes described in these proceedings reportedly can revert to normal within one week. However, many endurance athletes don’t wait seven days before embarking on another endurance training run or race. Months to years of continued overload on the heart may lead to patchy myocardial fibrosis, particularly in the atria, interventricular septum and right ventricle, causing atrial and ventricular arrhythmias. Additionally, data from a variety of animal and human studies suggest long-term excessive sustained exercise may induce coronary artery and coronary plaque calcification, diastolic dysfunction, abnormally large atria and large-artery wall stiffening. So much for that ultra-healthy body athletes might think they’re getting from living the ultra-endurance lifestyle.
The Heart of the Matter
The Mayo Clinic report reviewed about 50 studies published between 1991 and 2012 on the health effects of extreme endurance training and competition. One study showed that an estimated12% of apparently healthy marathon runners had evidence of patchy myocardial scarring. The coronary heart disease rate during a two-year follow-up was significantly higher in marathon runners than in controls.
An online study in the Journal of Applied Physiology followed 12 veteran endurance athletes (ages 50–67), 20 control subjects (ages 52–69) and 17 young endurance athletes (ages 26–40). All participants were male. Cardiac magnetic resonance imaging on subject heart structure and function found no abnormal thickening of heart valves in the young athletes or the older adult controls. Fifty percent of the veteran athletes showed evidence of this myocardial fibrosis, which was determined to be directly proportional to the number of years spent training and the number of marathons and ultra-endurance marathons completed.
When people partake in excessive endurance activities multiple times over the course of many years, scar tissue can form in the heart and weaken the muscle or cause a rhythm disturbance, states Dr. Carl J. Lavie, one of the physician authors of the Mayo Clinic study. This damage is believed to be most profound in individuals over 40.
Who’s at Risk?
Dr. Jonathan Fong, a cardiothoracic and vascular surgeon at Ocala Heart based in Venice, FL., says there’s still much more information to be uncovered. “While the [Mayo Clinic] study presents intriguing findings about possible mechanisms for these changes, it fails to stratify athletes consistently into groups that are at higher risk outside of those ultramarathoners who train up to a marathon a day.”
My own thoughts based upon interpolation and extrapolation are that there will likely be a genetic predisposition toward cardiovascular effects of chronic ultra-endurance workouts. Until we can determine which patients are at highest risk genetically, individuals are left to consider the ‘inspiration for their perspiration.’”
Fong believes a parallel will be found “between an external metric (e.g., pulse, blood pressure, respiratory rate) and an internal level of stress substances circulating in our systems, which cause microscopic cellular changes over extended periods of time.”
Both the German and the Swedish studies also suggest that genes may play an integral role in determining one’s “safety threshold” for intensive exercise.
Investigations such as routine blood work, EKG (electrocardiogram), echocardiogram and a cardiac CT scan would at least set baseline findings against which serial exams performed throughout training might be compared.
Lead author and cardiologist at Saint Luke’s Hospital of Kansas City, Missouri, Dr. James O’Keefe, Jr., also believes further investigation is needed to identify the individuals at risk for adverse cardiovascular remodeling, and to formulate physical fitness regimens that optimize cardiovascular health and longevity.
The Mayo team of doctor authors tentatively concluded that one hour of daily aerobic exercise is healthy for the heart and anything beyond that has diminishing returns and may cause adverse effects in some individuals. Cardiologist O’Keefe typically recommends to patients that they do their marathon or long-distance cycling or multisport event and then cross it off their bucket list, going back to an exercise pattern more likely to produce health benefits and improve longevity.
Dr. Fong recommends that patients follow American Heart Association® guidelines. But he has learned from experience that many endurance athletes have other objectives in mind. “Those that seek to test their limits are unlikely to pursue a more sedate exercise even in the face of the Mayo Clinic’s observations,” he states. “They are willing to sacrifice longevity to push the limits of human endurance.”
Dr. Lavie, study co-author and cardiologist, says physicians should ask patients about their exercise habits and offer suggestions on how they can make workouts safer.
“A physician should be consulted before any ultra-endurance training is undertaken,” Dr. Fong advises. “Family history and existing health conditions or cardiovascular risk factors should be weighed and limits set if significant associated risk is noted.”
Despite this bank of evidence against the safety of ultra-endurance exercise, runners have a 19% lower risk of all-cause mortality compared with non-runners, according to a 15-year observational study of 52,656 adults. The unpublished study was presented at a 2012 American College of Sports Medicine meeting in San Francisco. The biggest decrease in all-cause mortality was observed in runners who trained two to five times per week, completing 0.1 to 19 miles per week at speeds of 6 to 7 mph.
Fitness professionals should continue to urge their clients away from the couch. Most people get too little, rather than too much exercise. Working out is still the best way to prevent obesity-related illnesses, such as diabetes and hypertension. People who exercise regularly have lower rates of disability and a life expectancy seven years longer on average than couch potatoes. AF
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Susan Dawson-Cook has an MS from the University of Arizona, is a contributing writer for American Fitness, and publishes dozens of fitness and competitive swimming features annually (www.susandawson-cook.com). Employed in the fitness industry since 1988, Dawson-Cook is an AFAA certified group exercise instructor and personal trainer. She recently published a romantic sports suspense novel, The Open Water Swimmer, under the pen name Sabrina Devonshire (www.sabrinadevonshire.com).
ANNUAL MEETING OF THE AMERICAN COLLEGE OF SPORTS MEDICINE, HELD FROM MAY 29 TO JUNE 2, 2012 IN SAN FRANCISCO.
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