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A few weeks ago the Wall Street Journal published a piece titled “The Potential Cardiac Dangers of Extreme Exercise”, the article focused on a new, not-yet-published study suggesting that marathon runners might have more calcium buildup in the coronary arteries that feed the heart. The alarming headline aside, the article was balanced and it highlighted one of the big media stories in the exercise physiology and preventive medicine fields over the last couple of years. The idea is that while exercise and physical activity are clearly good for health, people who do a whole lot of hard training might not be getting all of the health benefits of exercise.

In other words, the too-much-exercise advocates believe there is a U-shaped dose-response curve with the maximum health benefits occurring somewhere between 30 and 60 minutes per day. More than that and there is no additional health benefit. Indeed, they argue that with a lot more at least some of the protective effects of exercise on mortality are lost. To take it further, the proponents of the too-much-exercise narrative believe that “extreme” levels of exercise can damage the blood vessels that supply the heart and also cause cardiac fibrosis and electrical problems.

The first part of the story about a flattening of the dose response curve is well known, the second part is highly controversial. The second part also tends to alarm a lot of serious athletes, especially master athletes who do things like marathons, triathlons and various ultra-events. The too-much story also generates a lot of emails, phone calls, and hallway conversations for physicians like me who do exercise physiology research.

So here are a few reassuring things to think about when you hear the speculation about too much exercise:

  1. The population studies on this topic provide a mixed message and many suffer from methodological limitations. Some say there is no uptick in mortality, some say there is. If there is an uptick it is small. Also, there are so few people who really train hard for decades that the whole topic is really challenging to study. When I get a call from the media about this topic I tell them that for every study supporting the too much speculation, I can show you one that rejects it. My favorite study on the topic followed about 50,000 cross-country skiers in Sweden who finished the 90km Vasaloppet race. The authors then used the Swedish medical records system and showed that mortality over a 10-year period was about half of predicted for the skiers and even lower for cardiovascular disease. For the sake of the too-much story, older people who did more races were even more protected that those who did fewer. Strike one for speculation about too much exercise?
  2. In the late 1950s seven-time Boston Marathon champion, 1924 Olympic marathon bronze medalist and pioneer master athlete Clarence DeMar (he won Boston at age 41 and competed until his mid-60s) died of cancer at age 70. An autopsy was performed on DeMar and while he did have evidence of significant plaque buildup in his coronary arteries, guess what? His arteries were absolutely huge. Later studies on ultramarathoners showed that these athletes had big coronary arteries that could really open up compared to sedentary people. The same is true in older people who exercise vigorously. A lot of the too-much-exercise story is about potential calcium build up in the coronary arteries. I tell people that all things being equal I would rather have big coronaries that can open wide, and that a lot is unknown about what exactly coronary calcium means, especially in fit people. Strike two for speculation about too much exercise?

  3. The physiology story on the fibrotic heart question is equally reassuring. The research group led by my colleague Ben Levine in Dallas has shown in a number of studies that life-long heavy trainers have hearts that are as compliant and flexible as young people. Strike three for speculation about too much exercise?
  4. The final question is about electrical problems in the heart. Here the evidence for lifelong heavy training increasing the risk for atrial fibrillation and problems with excessively slow heart rates is better but not ironclad. However, again, many of the studies supporting increased risk have some limitations. To go back to the Swedish skiers, with more and faster races there was a small increase in the risk of atrial fibrillation. When all 50,000 skiers are compared to what might be expected from other large studies, the men in the 55-64 age group showed a rate of atrial fibrillation (49 per 10,000 person-years at risk) about twice that seen in other large studies. However, the authors of the study point out that it is possible that athletes, who are used to monitoring how they feel, notice “funny heart beats” more easily and are faster to seek medical attention. So perhaps some increased risk but certainly not dramatic, and the skiers showed no evidence of increased risk for the type of electrical problems that kill people and cause sudden death.

The two final points are pretty simple, while exercise is protective it is not a vaccine and case reports of people who were lifelong exercisers dying during exercise do happen but they are rare. The second, and the one that the advocates of the too-much-exercise story typically miss, is that while people doing heavy lifelong training are doing it for their health, they are mostly doing what they do for far more than their health. Many are pursuing challenges and goals that go far beyond simple return on investment thinking about longevity and are focused instead on adding life to their years.

Michael Joyner, is an expert in human performance at the Mayo Clinic, these views are his own. You can follow him on twitter @DrMJoyner.