All runners have heard about the tragedies. The marathoner Alberto Salazar, at the age of forty-eight, suffered a heart attack and lay dead for fourteen minutes before a stent opened up a blocked artery and saved his life. Micah True, the ultra-marathoner at the center of the best-selling book “Born to Run,” went for a twelve-mile run in the New Mexico wilderness and was later found dead. Ryan Shay dropped dead in the middle of the 2008 United States Olympic marathon trials. There is also the story of the first marathon itself, run by Pheidippides, who, after completing the 26.2 miles, collapsed and died. These deaths are all the more shocking because the peak physical condition of the deceased would seem to protect them from heart disease. Hundreds of studies, as well as our own intuition, associate exercise with cardiac health. But, in recent years, a small group of cardiologists have advanced a hypothesis that suggests these tragedies may not be so shocking, after all: they believe that an excess of exercise actually damages the heart.
The most vocal proponent of the too-much-exercise theory is James O’Keefe, a cardiologist and the director of preventive cardiology at the Mid America Heart Institute, in Kansas City, Missouri. In a TEDx talk in 2012, as well as in a series of editorials and reviews, O’Keefe has argued that exercise beyond a certain threshold can lead to heart disease, and possibly decrease the benefits of moderate exercise. In a video accompanying a review he co-authored titled “Potential Adverse Cardiovascular Events from Excessive Exercise,” O’Keefe suggests that extreme exercise is “not conducive to great long-term cardiovascular health,” and cautions against the assumption that, if moderate exercise is good, more must be better. “Darwin was wrong about one thing,” O’Keefe says. “It’s not survival of the fittest but survival of the moderately fit.”
For those of us who believe that the “everything in moderation” rule applies to, well, everything, this argument makes sense. Exercise remains one of the best things you can do to improve your cardiovascular health, but you certainly do not need to run marathons to achieve the benefits. Moderate amounts of exercise throughout life are perfectly adequate. Athletes who exercise in extremes generally do so for reasons other than their health—competitiveness, professional requirement, compulsion. But recognizing that exercising more than a certain amount reaps no greater cardiovascular benefits is quite different than suggesting that this level of exercise causes cardiovascular harm.
O’Keefe argues that exercise beyond a certain threshold increases cardiovascular risk. Given the complexity of the heart, the argument is tough to unpack. For the heart to do its job, the coronary arteries must be open, the electrical impulses need to be coördinated and rhythmic, and the muscle itself must be able to relax and fill. Exercise affects these systems both directly and indirectly, by mitigating the many risk factors, like obesity and high blood pressure, that cause heart disease in the first place. Because exercise affects all these systems, O’Keefe can be both right and wrong at the same time.
First, the bad news for marathoners and other extreme athletes. Excessive exercise has been consistently associated with atrial fibrillation, a rhythm disturbance that increases the risk of stroke and leaves some people feeling weak and breathless. One study looked at the rates of atrial fibrillation in over fifty thousand Swedish men who had participated in the Vasaloppet, a ninety-kilometre cross-country ski event, over a ten-year period. Those who completed the most races or who had the fastest times seemed to have a higher risk of atrial fibrillation.
So how high is this risk? The magnitude varies, but some reviews suggest that the risk of atrial fibrillation for extreme athletes may be increased five fold when compared to sedentary people. While this sounds drastic, Brian Olshansky, a heart-rhythm specialist in Iowa and an avid runner (every cardiologist I spoke to who studies this issue is a current or former endurance athlete), helped put the risk in context: “Let’s say one’s lifetime risk of atrial fibrillation is 0.3 per cent,” he said. (The risk varies depending on several factors, like age and obesity.) “A five-fold increase still leaves your lifetime risk of atrial fibrillation at only 1.5 per cent.”
Risk estimates can be hard to wrap your head around, though, because no matter how well we can predict the likelihood of something happening in the future, once it happens it hardly matters what the likelihood was in the first place. This may be why John Mandrola, a heart-rhythm doctor at Baptist Medical Associates, in Louisville, Kentucky, increasingly cautions against extreme exercise. Mandrola was an élite cyclist for decades, and a few years ago he crashed his bike. Despite painful rib fractures, he quickly resumed riding; twenty miles into his first ride after the crash, Mandrola became acutely short of breath and dizzy, and he lost his muscle strength. The butterfly sensation in his throat had been described to him several times by his own patients: he was in atrial fibrillation.
Once his immediate fear of stroke passed, Mandrola’s fears became existential: Had his life changed irreparably? For years, he had been a cyclist who also happened to be a cardiologist. Now he was just a cardiologist. Some scientists postulate that inflammation may play a role in atrial fibrillation, and Mandrola began to see his earlier hard-driving life-style choices as “the inflammation of excess.” He believes that an endlessly striving, never-enough mind-set begets ill effects far beyond those we can attribute to excess physical activity. “It’s not just being on that edge in a race,” he told me. “It’s being there in training, at home, at work, and for decades. Always on the gas—yes, this is the problem.”
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Like Mandrola, O’Keefe was once an über-exerciser. He won Kansas City’s sprint triathlon five years in a row. Then, in midlife, he decided to change his ways. At the beginning of his TEDx talk, reflecting on his previous exercise habits, he says, “I’m worried I may have made a lethal mistake.” In the editorial, which largely mirrors the TEDx talk, O’Keefe and his colleague Carl Lavie suggest that vigorous exercise should be limited to “thirty to fifty minutes per day.” They conclude that “running too far, too fast, and for too many years, may speed one’s progress toward the finish line of life.” The editorial received widespread and mostly alarmist media attention, including an article in the Wall Street Journal titled “One Running Shoe in the Grave.”
Is there any reason to believe that O’Keefe’s years of endurance competition will shorten his life, or worsen his cardiovascular health? At this point, no. First of all, other studies, most of which come from Paul T. Williams’s National Runners’ Health Study, suggest that risk factors for cardiovascular disease continue to improve with increasing amounts of exercise. When it comes to the specific association between extreme exercise and mortality, statistically rigorous associations are hard to come by, because in any given population relatively few people exercise in an extreme way, and even fewer still die during the study.
For example, one study cited by O’Keefe to suggest that mortality benefits are lost with increased exercise looked at mortality rates among nearly eighteen thousand runners in Copenhagen. The authors of the study, published in the American Journal of Epidemiology, confidently concluded that, when compared to non-joggers, runners lived, on average, five to six years longer. But, in their discussion of whether more intense exercise was associated with harm, the authors were far more circumspect: “We don’t have evidence to support faster or more frequent jogging, nor do our limited data rule out the possibility.”
Another study cited in O’Keefe and Lavie’s editorial found that, in over four hundred thousand people in Taiwan, forty-five minutes of vigorous exercise daily was associated with a forty-per-cent decrease in risk of death. In describing this study, O’Keefe and Lavie note that “at about forty five minutes, a point of diminishing returns is reached whereby longer exercise efforts do not appear to translate into lower death risk.” They go on to compare exercise to a drug, an analogy O’Keefe frequently invokes. “As can be expected with any potent drug, an insufficient dose will not confer the optimal benefits, while an excessive dose can cause harm, and even death in extreme overdoses.”
But, prior to the publication of the editorial, O’Keefe and his colleagues wrote a letter to the authors of the Taiwanese study. They asked whether the Taiwanese data really suggested that excessive exercise can be deleterious. The letter is cited in the editorial, but the response, published simultaneously and written by the study’s lead author, Chi-pang Wen, is unmentioned. Wen writes, “We were not able to identify an upper limit of physical activity, either moderate or vigorous, above which more harm than good will occur in terms of long-term life expectancy benefits.”
When I asked O’Keefe to comment on Wen’s response, he noted that what was considered “vigorous” exercise in the Taiwanese study was far easier than what doctors in the U.S. would consider vigorous. He thus remains concerned about high-intensity, long-duration exercise, like marathons. While acknowledging that all the data we have is observational, and therefore “speculative,” he maintained that “while it doesn’t appear that overdoing exercise shortens longevity, it does appear to blunt the otherwise unrivaled improvements in life expectancy conferred by less extreme amounts of exercise.”
After reviewing the data and interviewing experts in the field, my own impression is that among people without known cardiovascular disease there is no compelling data to suggest that mortality significantly differs between moderate and extreme exercisers. There is thus no way to precisely define an upper limit of exercise for an average healthy individual. I suspect, though, that part of what sustains the “too much exercise can kill you” myth is the widespread recognition of the so-called exercise paradox. That is, while consistent exercise decreases the likelihood that you will have a heart attack, if you are destined to have one it is more likely to happen while you are exercising. That’s why no one can issue a blanket statement that extreme exercise is safe. It’s also why so many researchers have attempted to figure out how to make extreme exercise as safe as possible.
One study, led by Aaron Baggish and Jonathan Kim and published in the New England Journal of Medicine, examined rates of cardiac arrest among eleven million marathoners and half-marathoners over a ten-year period. Fifty-nine cases of cardiac arrest occurred during a race, translating to about one cardiac arrest for every hundred and eighty-four thousand participants over-all. Men were at a greater risk than women, and the two leading causes of death were hypertrophic cardiomyopathy (the leading cause of death among young athletes) and coronary artery disease.
In a related study that assessed the heart size and function of sixty non-élite Boston marathoners, Malissa Wood and Tom Neilan found that, immediately following the race, a percentage of runners had evidence of heart-chamber enlargement and increased stiffness. (Wood has been one of my mentors in cardiology since 2006.) Additionally, two of the enzymes that signal heart-cell damage became slightly elevated in just more than half of the marathoners. This helps explain why exercise can unmask existing disease. As Wood explained, “If even the healthiest hearts after a marathon leak a heart enzyme or demonstrate reduced pumping function, those with sick hearts will have trouble.”
Does this mean that non-élite runners should refrain from marathons? Absolutely not. There are some key messages about how to exercise safely that have emerged from these studies and others. The first is to train adequately. Perhaps the most important finding from Wood’s study was that the degree of detectable damage was lowest, or completely absent, among those who had trained by running more than forty-five miles a week, as opposed to those who ran thirty-five or fewer. Second, while exercise is one of the best things you can do to prevent cardiovascular disease, exercisers are not immune. Beginning an intense exercise regimen in midlife cannot suddenly erase coronary artery damage resulting from, say, years of smoking or uncontrolled blood pressure. Finally, if you have risk factors for heart disease, including a family history, those should be addressed with a physician prior to starting an intense exercise regimen. We can outrun lots of things, but we can’t outrun our genes.
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The phemomenon known as identity protective cognition, or motivated reasoning, can help explain our general propensity to dismiss data that might threaten our fundamental sense of who we are or what we believe. Daniel Kahan, a Yale law professor, has studied this tendency extensively, particularly around the intense polarization of issues such as climate change, gun control, and vaccines. While exercise and the heart will not strike many as a particularly polarizing topic, exercise science, in general, serves as fertile ground for motivated reasoning. Like what we eat or which clothes we wear, exercise is wrapped up in our life rhythms. You can choose not to exercise, but you can’t escape having to make that choice. We constantly see happy, healthy exercisers; for some people this is motivating, but for others—those who find exercise a unique brand of torture—it fosters a sense of inadequacy and guilt. Science, in all its iterations, becomes a source of validation. When that science contains conflicting results, derived from studies of varying rigor, our identities often emerge to guide us through the data.
While our need for identity preservation can affect the way we derive meaning from science, it is also true that science often cannot tell us what gives people meaning. Ours is a society that is simultaneously unhealthy and obsessed with health. Scientific studies about exercise, diet, or other life-style choices seem to be read and shared more than any other kind. Is this because we are seeking health, or because we’re looking for confirmation that our approach to life is healthier? As Alex Hutchinson, writing for Runner’s World, has noted, each time the suggestion that too much exercise is harmful makes the news “it invariably rockets around the cybersphere powered by schadenfreude.” Of course, some behaviors are healthier than others, and some invoke more envy or disgust. But whether we prefer to binge on exercise, Netflix, or donuts, our chosen vices often reflect far more than the pursuit of any objective health outcome. Science is an invaluable resource to help people lead healthier lives, but it should not be a weapon to shame and frighten people who don’t, or who can’t.
