Running has so many health benefits, it’s counterintuitive to consider any negative effects endurance training may have on the body. However, research suggests that some runners may be at higher risk for atrial fibrillation, also known as A-fib. A-fib is an irregular, rapid, fast-pounding heart rhythm, or palpitations.
While often temporary and not worrisome, A-fib can have potentially serious consequences. Here’s more about the research, what you need to know about A-fib, and why you don’t need to panic.
What Research Says About Atrial Fibrillation and Exercise
While previous research has shown that male runners can be prone to atrial fibrillation with high-volume, vigorous exercise, the risk for female athletes was understudied. But earlier this year, research has revealed that women are also susceptible.
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According to a cohort study released in May 2022 in EP Europace, a peer-reviewed medical journal specializing in cardiac health published by Oxford University Press, researchers found an association between a high-level of endurance sport training and increased risk of atrial fibrillation in female athletes.
Before you immediately stop your vigorous workout routine, keep in mind that it is likely only athletes with a family history of A-fib, a history of cardiac surgery, or those with sleep apnea, among other risks, that may be more susceptible to developing A-fib. Simply put, these prior conditions can get exacerbated with vigorous long-term exercise and lead to risk for A-fib.
In the study, “high-endurance training” was defined by both distance and speed, and the researchers looked at more than 200 women who fit three categories: marathon runners with times faster than 3.25 hours, top ranked cyclists, and national champion 10,000-meter track runners. All the athletes were competitive from 1979 to 1991. The researchers found that, nearly 30 years later, the sample pool reflected a 4.4% occurrence of A-fib compared to a 1.7% among the non-athlete population.
“A-fib is definitely a hot topic among my patients, particularly discussing A-fib risk and sport intensity. A lot of athletes ask if there is a correlation between exercise and lone atrial fibrillation—meaning, there’s no other risk factor of heart disease,” says Tamanna Singh, M.D., codirector of the Cleveland Clinic Sports Cardiology Center. “The data we have says there is an increase of lone A-fib in high-intensity and high-endurance athletes with no other risk factors.”
In addition to the study released this year, involving female athletes. Other, old research also supports this correlation between high-intensity exercise and atrial fibrillation risk. For example, one study from the European Society of Cardiology identified a U-shaped curve of incidence which demonstrated that some high-intensity exercise protected individuals against A-fib, but too much or too little could exacerbate the issue. In fact, individuals that exercised for a limited number of hours (under 2,000 hours over a lifetime, to be exact) held the lowest risk for A-fib, compared to sedentary athletes and extreme athletes that did more vigorous activity. A-fib risk for endurance athletes was associated with 2,000 hours or more of lifetime-accumulated, high-intensity endurance training.
Another study from the European Society of Cardiology analyzing more than 20,000 adults, and involving a 20-year follow-up, saw evidence that moderate physical activity (like walking and cycling) reduced risk of A-fib and helped to protect heart health. Meanwhile, higher activity levels (like hard training and sports competitions) attenuated those benefits, due to cardiac adaptations that occur over the course of years. This study also found an association between low resting heart rate, which is common in athletes, and A-fib.
What Happens to Your Body When You Have A-Fib
Everyone has felt their heart flutter or skip a beat for a moment or two, but A-fib is more intense and long-lasting. When your heart works properly, we don’t even notice it beating, but when there’s an issue, we can feel it immediately.
Your heart has two upper chambers, which receive blood, and two lower chambers that pump blood out. An electrical conduction system regulates this movement between the upper and lower chambers. “The normal electrical conduction system is very well defined, and that normal rhythmic electrical system moves from the top of heart to the bottom and you can feel your pulse in a normal pattern,” says William Cornwell, M.D., associate professor of medicine-cardiology at the University of Colorado Medicine.
A-fib, on the other hand, involves irregular electrical impulses in the atrium, one of the two upper heart chambers, explains the Cleveland Clinic. As a result, the upper chambers are out of sync with the lower chambers.
“Basically, you have these electrical hot spots that occur in areas of change. Those electrical hot spots or pulses propagate to the crux of the heart, or the atrioventricular node, which carries and transmits those pulses to the bottom chambers of heart and causes irregular contractions,” explains Singh.
“It’s not entirely clear why A-fib happens in endurance athletes,” Cornwell explains. He says it’s possible that endurance and dynamic exercise can enlarge the heart and atria. This can then lead to a development of fibrosis or a scar formation, causing inflammation that interferes with the electrical conduction system and causes chaotic A-fib.
Reaching an Atrial Fibrillation Diagnosis
For those who have, A-fib, there are four general severity levels, which can make getting a diagnosis a long process.
“Occasional, or paroxysmal atrial fibrillation, is when A-fib symptoms come and go for athletes and is typically in masters athletes and older,” says Singh. “One example would be if someone has been drinking alcohol and they are dehydrated, and that can be precipitant the next day for A-fib for a couple of hours, but nothing that lasts longer than a week.”
The next level of severity can last longer. “Persistent A-fib lasts more than seven days,” says Singh. “You’re not returning to a normal rhythm on your own, and treatment is needed to convert you back to the normal rhythm.
Even more continuous, long-standing A-fib lasts longer than 12 months, which is treated with invasive procedures or convert strategies like electrical cardioversion, which is when the heart is shocked to convert it back to a normal rhythm.
When an irregular heart rhythm that can’t be restored, the athlete has permanent A-fib. In this case, patients take medications to prevent blood clots and moderate the heart rate.
Other Atrial Fibrillation Risk Factors
“We typically see A-fib increase after age 60,” says Singh. Though not common, she also sees A-fib in young athletes in their late teens or early 20s with infrequent, short episodes of A-fib.
Often masters athletes diagnosed with A-fib have underlying cardiac issues, such as high blood pressure, heart disease, a prior heart attack, or valve-related issues like leaky or narrowed valves—basically, any structural changes to the heart, Singh explains. Or, they have a genetic predisposition to cardiac health issues.
“A-fib will come from a structural change in left atrium. You can have those changes with a health condition like sleep apnea too,” Singh says.
Other risk factors for atrial fibrillation exist outside of an exercise routine and history of heart problems, though. Those include diabetes, alcohol consumption, thyroid problems, and other medical conditions, according to the American Heart Association.
Symptoms and Side Effects of Atrial Fibrillation
In addition to a fluttering heartbeat, A-fib patients may experience chest pain, shortness of breath, dizziness, fatigue, lightheadedness, and weakness, according to Mayo Clinic. If you experience symptoms or signs, talk with your physician and they can order a handful of different tests, such as an electrocardiogram (among others), to help diagnosis the condition, and rule out other conditions with similar symptoms.
Sometimes, though, athletes don’t notice A-fib symptoms and it remains undetected, which can lead to changes in the heart muscle. This is a problem because A-fib can have long-term effects. “With constant irregular pulses going to the heart with an irregular contraction, you lose that synchronized contraction that optimizes blood flow to the rest of body. That poor output to the body can lead, over time, to cardiomyopathy,” says Singh.
Cardiomyopathy makes it harder for the heart to pump blood through the body, which can lead to heart failure. This is why it’s so it’s important to identify and treat A-fib.
Another A-fib concern is that it can cause blood clots, which increases the risk of stroke, causing those with A-fib to be at higher risk for stroke, according to the American Heart Association.
Treatment for Atrial Fibrillation
Ultimately, the aim for A-fib treatment is to revert the heart rhythm back to normal and also to prevent blood clots. Depending on the level of A-fib that’s detected, A-fib treatment is tailored to each patient.
To determine the best course of care, a cardiologist will first identify if there are underlying comorbidities (the presence of two or more diseases) in an athlete, says Singh. In these cases, sometimes treating an underlying condition can help control A-fib.
In general, athletes with occasional a-fib and no other underlying health issues can take medication that slows down their heart rate or heart rhythm to convert it back to a normal heart rhythm, says Singh.
Patients may also go through electrical cardioversion, a procedure that uses quick, low-energy shocks to restore a regular heart rhythm.
“Competitive athletes with symptomatic A-fib, we usually proceed with catheter approach or cardiac ablation. You can go directly to the areas that are electrically hot and causing A-fib and burn those areas,” says Singh.
How to Prevent Atrial Fibrillation
The question on every runner’s mind: Should you change your exercise behavior to prevent A-fib? As with most answers to health questions, it depends. But one thing is certain: You shouldn’t stop moving. Moderate exercise helps reduce the risk and frequency of A-fib, says Singh.
“I generally don’t recommend people stop exercising due to occasional A-fib, because the exercise is having a positive effect on other factors that would contribute to your increase of stroke and comorbidity [risk],” says Cornwell.
“It’s a little hard to quantitate, but if you are a couch potato and don’t exercise at all, the risk of A-fib is higher over your lifetime than for people who regularly exercise and follow the recommended guidelines,” Cornwell adds, referring to the Physical Activity Guidelines for Americans. These guidelines suggest 150 minutes a week of moderate-intensity aerobic activity or 75 minutes of vigorous aerobic activity, as well as muscle-strengthening activities on two or more days per week.
“Your risk drops if you follow those weekly guidelines. If you start to exceed those guidelines and get into the elite endurance type of athletics, the risk of A-fib goes up,” Cornwell explains, but that doesn’t directly mean your risk of serious cardiac events goes up, too.
Your decision should also be in line with your risk factors. “Controlling risk factors is important: If you know you have high blood pressure, for example, control those structural changes made by high blood pressure, so you can minimize your risk of A-fib,” Cornwell adds.
For athletes that are susceptible to heart disease, it’s key to control cholesterol levels and not be sedentary to reduce the risk of A-fib. Also, keep alcohol and stimulant use at a minimal level, Singh says.
Remember, Running is Good for Your Heart
Running consistently over an average 5.9 years revealed a 50 percent lower risk of cardiovascular mortality compared to never-runners, according to a 2014 study published in the Journal of the American College of Cardiology.
And while cardiovascular diseases (CVDs) are the number-one cause of death around the world, reports the World Health Organization, a large variety of cardiovascular diseases exist. They range from coronary heart disease, which affect the blood vessels supplying the heart muscle, to rheumatic heart disease, in which there is damage to the heart muscle and valves following a case of rheumatic fever.
So, while A-fib can lead changes to the heart muscle that increase cardiovascular mortality, A-fib is not a direct cause of heart failure, explains Singh.
More good news: A recent report published by the American Heart Association and American Stroke Association, which Cornwell co-authored, researchers outlined a large analysis of Swedish cross-country skiers, which showed that exercise is able to decrease stroke risk factors well enough that those benefits offset the increased stroke risk associated with atrial fibrillation.
The Bottom Line: What to Know About Atrial Fibrillation and Exercise
Ultimately, it’s essential to pay attention to and treat A-fib, so see a doctor if you suspect you have it, but don’t sacrifice your workouts unless you are told to do so.
“High-intense, high-volume exercise slightly increases the risk of A-fib—but that’s not a reason to stop participating in a sport,” says Singh. “A-fib can be managed, and the benefits of exercise far outweigh that risk, especially because cardiovascular disease is the number-one killer of men and women in United States.”
Morgan Tilton writes about the outdoors with a focus on travel, industry news, and human endurance. Her work is featured in more than 70 publications, and she’s a recipient of many North American Travel Journalists Association awards, including double-awards for the essays, “Wild & Broken: A First SUP Descent of Utah’s Escalante River” and “A Wild Space.” Morgan grew up mountain biking, hiking, and playing in Colorado’s San Juan Mountains before moving to Crested Butte, in the adjacent range.