Everything in moderation right? Even exercise? So how does marathon running and all it’s training fit into the scales? Here’s a surface look at science and the heart.
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. 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.
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.
* * *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.
* * *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.