Will Endurance Training Kill You?

Last weekend I rode the 78-mile Copper Triangle event with my 11-year-old son, Connor. It was his longest ride ever, in mileage, elevation gain, and time on the bike. He did great and I loved sharing the experience and the day with him. As we both climbed Vail Pass with our hearts pounding away, I thought about the recent “Cycling to Extremes” article in Velonews and the questions people have been asking me about it. So, after consulting with cardiologists, cardiac surgeons, and electrophysiologists, here are some initial thoughts on the matter.

If you haven’t read the article, the quick summary goes like this: Some endurance athletes develop cardiac problems, including myocardial fibrosis (stiffening and thickening of the heart muscle), atrial fibrillation (an electrical problem that causes atria to quiver instead of pumping blood properly), or other types of tachycardia (an abnormally high heart rate that may feel like your heart is pounding or “skipping a beat”). The question is whether long-term participation in endurance sports increases an athlete’s risk for developing these conditions, and the article leans heavily in the direction that it does.

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This is obviously a cause for concern for many athletes. I’m almost 55 years old and I’ve been training and competing since I was 9. What did I do after reading the article? I went for a bike ride, complete with intervals, and I was far more worried about getting run over by a distracted driver than about potentially damaging my heart.

The physicians I’ve consulted since then generally agree with me. On balance, they believe the health benefits of exercise – including strenuous exercise – outweigh the risks of developing electrical or structural problems within the heart by a large margin. That’s not to say the risk isn’t there, but rather that exercise is only one of many factors that contribute – positively and negatively – to the health of your heart.

But that’s not really news. Everyone knows that some exercise is better for you than none, and for the people who read this blog and send me emails, the choice is not between their current training workload and nothing at all. You’re not going to hang up your wheels and just sit on the couch. What athletes are struggling with now, in light of this recent article, is the choice is between strenuous exercise and a more leisurely level of activity.

Here are a few things to consider:

Cardiac problems are extremely rare for CTS Athletes

In the past 15 years CTS Coaches have worked with more than 15,000 athletes. We are neither physicians nor medical researchers, but in that time we know of only a handful of athletes who have developed heart rhythm issues (AF, etc.), structural heart issues (fibrosis), or suffered a heart attack or stroke while exercising. How do we know? During an athlete’s coaching program, they have the opportunity to put a medical hold on their membership, and we ask them about their medical condition. When athletes stop working with CTS we ask why they are leaving. As part of our quality assurance program we also ask the coaches for information about athletes who cancel. The few athletes who have developed AF were open and eager to telling us, which leads me to believe other athletes would be similarly honest and forthcoming. Yet we are not seeing any increase in the number of athletes reporting arrhythmias or other cardiac problems.

CTS is probably one of the largest endurance coaching companies in the US. The vast majority of the athletes we coach are men between the ages of 40-65. Some have been training consistently for 30+ years and others are relatively new to endurance sports. All of them do interval training. If years of cumulative endurance training – including high-intensity training – were leading to a significant increase in arrhythmias in athletes over 40, I would expect we would be one of the first organizations to see it happening. It would be troubling and noticeable if more and more athletes were requesting medical holds or cancelling or dying because of cardiac health problems. But we are not seeing that at all.

You know what we do see a lot of? Cancer. At any given time of the year there are a significant number of athletes on medical holds because of cancer. I know of one athlete who has been on hold for an entire year; he’s not cancelling because the idea of coming off hold and returning to training provides him with motivation and hope.

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Atrial Fibrillation diagnoses are increasing in the overall population

The incidence of AF naturally increases with age and there are an estimated 75 million Baby Boomers (age 51-69 in 2015) like me who have reached an age when genetics and decades of lifestyle choices start expressing themselves. Things start going wrong, like your heart’s electrical system. So, if there is an increase in the number of AF diagnoses in athletes over the age of 50, perhaps it is because we are representative of a growing population of people over 50. The physicians I consulted also commented that technology has improved their ability to detect arrhythmias earlier, so more people of all ages are finding out they have them. Indeed, this study of 50-year trends of atrial fibrillation indicates the increases in incidence and prevalence are at least partly due to increased effort and efficacy of looking for them.

A lifetime of factors contribute to cardiac health and disease risk

The decisions you have made in the past 4-6 decades have made you what you are, for better and worse. High-stress careers can be rewarding and lucrative, but being a hard-charging Type-A person means dealing with a lot of stress. Maybe you thrive on it, but your body can still be negatively affected by it. And not all 50+ athletes have been athletes for their entire lives. Many athletes we coach spent decades gorging on cardiac risk factors: excess body weight, high cholesterol, high blood pressure, poor eating habits, little to no exercise, high-stress environments, heavy drinking and/or recreational drug use, and smoking. Dropping bad habits and becoming an athlete have done these people a ton of good and probably saved some of their lives, but good habits in the past decade may not completely negate or reverse the damage you did decades ago.

Even before your good and bad habits started building your profile for cardiac risk factors, your genetics dealt you a hand to play. Those cards may predispose you to high cholesterol, or blood clots, or arrhythmias. Could high-intensity exercise help to reveal an underlying problem? The physicians I consulted said yes. But they also said it’s likely not just the exertion, but a combination of acute factors like lifestyle stress, fatigue, dehydration, prescription drug interactions, heat stress… and exertion. A physician who specialized in electrophysiology pointed out that experiencing an arrhythmia isn’t a sure sign of a life-threatening or long-term problem. Even a perfectly healthy heart can skip a beat or race briefly and return to normal rhythm. Athletes are also more attuned to their bodies and sometimes notice arrhythmias before a sedentary person would. Further more, he pointed out that this could be a good thing if concern about these symptoms prompt the athlete to seek medical evaluation, making it more likely to discover an underlying cardiac issue, if there is one, sooner.

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We’ve seen this before

An article like the recent one in Velonews pops up at least once a year, although it’s typically been in running and triathlon publications or a large newspaper like the NY Times. The headlines warn that exercise can kill you, and the story cites a new study or some piece of evidence that may indicate those who exercise more have an increased risk of dying compared to those who perform more moderate levels of exercise. Alex Hutchinson, Ph.D., author of the “Sweat Science” blog on Runnersworld and the book “Which Comes First, Cardio or Weights”, has covered this topic extensively: “Will Too Much Running Kill You?”, “Heart Health and ‘Lifetime Exercise Dose’”, “The Too-Much-Running-Myth Rises Again”, and “The (Supposed) Dangers of Running Too Much”. There’s a lot of great reading in that list, as well as links to studies and subsequent commentary. Time and again, these articles and the subsequent discussions come back to the central premise that exercise is good for you, that more exercise is also good for you, and that there is a small percentage of the population that will push themselves too far and do damage to their bodies.

Where do we go from here?

The only thing I know for absolute certain is that we’re all going to die. The best we can do to prolong our lives is to continue doing things that reduce our risk factors for a wide range of diseases. Exercise – including strenuous exercise – is one of those things. But so is taking a more serious approach to rest and recovery.

The heart is a muscle, and like any muscle it adapts to stress. As an athlete you have a higher stroke volume (your heart pumps more blood per stroke) and a lower resting heart rate. These are positive adaptations from exercise. Just like any other muscle, recovery is key to maximizing positive adaptation and reducing injury risk. As such, it isn’t a huge leap to consider that overtraining or under-recovery may negatively impact the heart muscle in similar ways that under-recovery negatively impacts skeletal muscle, joints, connective tissue (ligaments and tendons), and the immune system. It is my belief that structured training that incorporates appropriate amounts of rest and recovery is instrumental in avoiding overtraining or under-recovery. Going back to the large population of CTS Athletes, the majority are what we call “time-crunched athletes” who train 3-5 days per week and have 3-6 weeks per year of either planned or unanticipated time (typically family or work related) away from training. In our population we’re not observing an increased incidence of cardiac disease or injury. So perhaps, if there is increased risk for athletes, it isn’t the workload or the intensity of the training that’s the problem, but rather the lack of recovery in poorly designed programs.

I guess there is one more thing I know for sure. I’m an athlete and there is no other lifestyle I would choose over this one. To this point in my life I believe being an athlete has kept me healthy, kept me from needing prescription drugs, provided me with a great and supportive community, allowed me to see the world from the saddle of a bicycle, and provided me with opportunities to spend my days riding shoulder to shoulder with my kids. Far from damaged, my heart is full of joy, and being an athlete is a big reason why.

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