The recent heart issues of professional cyclist Peter Sagan have again put the spotlight on endurance training. This wasn’t new for me: when my colleague, who had just completed an Ironman race (2.4-mile swim, 112-mile bike, and a 26.2-mile run), presented to the hospital with chest discomfort, I knew it was something serious. People who participated in these races were hard people who rarely complained. When I did his coronary angiogram, I was surprised to see the extent of blockages, with both plaque and calcium buildup. He needed bypass surgery, and all of us medical colleagues wondered how he hadn't dropped dead during the grueling 15 hours of racing.
He wasn’t the only one; another colleague who had done an Ironman race had a cardiac arrest a few months later. He was lucky that it was witnessed, and he was resuscitated. He needed an internal defibrillator. I was training for a similar distance race, and from time to time, on a 100-mile solo bike ride, I would feel some pangs of chest discomfort. I had one of my colleagues order a CT Coronary angiogram (CTA) on me, and I was relieved to see the smooth, normal arteries on the screen. Still, the question persisted: Was so much training good for the heart?
I looked around our group of 20-odd triathletes: six had documented heart-related disease, either established plaque development in the arteries or an irregular heart rhythm called atrial fibrillation. This anecdotal observation was consistent with the data from a Dutch study looking at coronary artery disease on a CTA in otherwise asymptomatic middle-aged athletes. The authors found that there was significant disease in 18.9% of this otherwise fit subgroup, with minimal traditional risk factors of obesity, diabetes, and smoking. This data leads to a few intriguing questions: Does more exercise protect against cardiac disease, or is it detrimental, and if so, why?
A study out of Belgium last year addressed the first part of the question, looking at lifelong endurance athletes who started training before the age of 30 years and comparing them to endurance athletes who began training after 30 years, with the control being similar-age individuals with moderate exercise (less than three hours a week). Endurance athletes ran for more than six hours a week, cycled for more than eight hours a week, or did triathlon training for more than eight hours a week. All the subjects were at low risk for developing disease based on current risk factors. The results showed that lifelong endurance training not only did not provide additional protection but could also be detrimental, with this group having more coronary plaque formation and a higher calcium score than the control group. The late-onset endurance athlete landed in the middle. Whether this plaque formation leads to more heart attacks or death is still a question.
The second part of the question, "why," has also been studied. The prolonged and repetitive mechanical stress causes a pro-inflammatory state, which leads to injury and plaque formation. Over time, fibrous tissue replaces healthy tissue, which leads to electrical disturbances like my colleague. Middle-aged endurance athletes have a fivefold risk of the development of atrial fibrillation when compared to their sedentary counterparts. Endurance exercise can damage a normal heart, as evidenced by leakage of cardiac markers like troponin and elevation of another marker called brain natriuretic peptide (a marker for congestive heart failure) after endurance sporting events. While these markers normalize in 48 hours, the endurance athlete is in an essential loop of continuous inflammation.
So how much exercise is too much for you? That's one of those existential questions: who are you? We are all built differently, almost like different models of cars. I, for example, need to use a lot more heart rate and cardiac output to achieve a certain speed than my friends in my group, who are more elite athletes. This leads to more vascular stress and inflammation for the same distance covered. Many other factors are involved: genetics, diet, sleep patterns, and stress. I repeated my CTA last week with an Ironman distance and multiple half-Ironman races under my belt over five years. I could see a few specks of calcium and mild plaques, but nothing to deter me from endurance training. Endurance training has taught me discipline and forced me into good nutrition and sleep patterns, not to mention being a huge stress buster. There is risk in everything we do, and death is inevitable. You have to decide if the risk is worth it.
What are your thoughts on the pros and cons of endurance sports and cardiac events? Share in the comments.
Dr. Arab is Director of Interventional and Structural Cardiology at AdventHealth, Daytona Beach and Clinical Assistant Professor of Medicine at Florida State University. His passions include triathlon, mountain climbing, and writing.
Animation by Diana Connolly
