Running with Heart: Analyzing the Effects of Ultrarunning on Cardiovascular Health
Exercise, particularly endurance sports such as running, has often been compared to a drug. There is little question today that the benefits of regular physical activity are many, from reduced risk of coronary artery disease and diabetes, to longer life expectancies and improved psychological well-being (Patil et al., 2012). This is truly a medicine that targets all aspects of health, both physical and mental. But, like any drug, there is an upper limit where consequences may exceed known benefits. And, of course, drugs can be deceptively addictive.
The sport of ultra-endurance running, or UER, has exploded in popularity over recent decades, with over 7,000 events around the globe in 2019, and more than 669,000 competitors taking part (Scheer et al., 2021). UER events, which involve running longer than a marathon distance, or 26.2 miles (42.195 km), can range from “beginner” 50ks to multi-day races that cover hundreds or even thousands of miles. Given its relatively recent increase in participation, few studies have analyzed the long-term effects of running so far, instead examining acute impacts, such as bone injuries or nutritional concerns (Scheer et al., 2021). Yet a growing number of researchers are seeking to understand how chronic multi-hour or multi-day runs restructure and reshape the human body – for better or for worse. And while there is much to celebrate about UER, including the positive effects and adaptations described above, there are also findings that raise alarm. Specifically, the cardiovascular system has been found to respond to ultrarunning, oftentimes profoundly, and the effects can be far from beneficial.
In 490 BC, Greek messenger Pheidippides was sent on several long missions during the Persian War to relay information for the Greek military. After covering approximately 150 miles in a matter of days, all on foot, the runner died suddenly following a message of victory, which he traveled 26 miles from Marathon to Athens to deliver (Patil et al., 2012). His death, and its apparent cardiac origins, led to the coining of the term ‘Pheidippides cardiomyopathy’ centuries later, an affliction resulting from chronic excessive endurance exercise (EEE). Indeed, studies have suggested that EEE can cause a long-term restructuring of the heart’s ventricles, allowing them to enlarge, sometimes by over 40% (Malek et al., 2019) and thicken (Patil et al., 2012). This reshaping of the ventricles has long been considered an expected characteristic of the “athlete’s heart,” and research has shown that over half of endurance athletes will undergo enlargement in the right ventricle (Scheer et al., 2021). When they undergo long periods of physical exertion, the heart stretches, eventually adapting to the increased shape after years of excessive exercise. But while a big heart isn’t really something to worry about, it is the subsequent evidence of aortic stiffness and calcification that is truly a cause for concern.
It has been suggested that the “shear stress” of chronic EEE causes “fibrotic changes” in the walls of the atria, eventually leading to “decreases in compliance” (Patil et al., 2012). A study of runners who had completed over 25 marathons in 25 years or less (defined as “long-term marathon runners”) demonstrated more calcification and plaque in the coronary arteries. Subsequent studies showed that long-term marathoners had levels of plaque similar to individuals with known coronary artery disease (CAD), and much higher than their non-runner counterparts (Patil et al., 2012). These cardiovascular adaptations can increase the risk of arrhythmias and atrial fibrillation, as well as other conditions such as ventricular tachycardia and fibrotic scarring. A 2014 study of male ultrarunners with more than five years of EEE experience showed decreased arterial compliance (increased stiffness) associated with longer distances, a phenomenon that indicates a heightened risk of a “cardiovascular event” (Burr et al., 2014). Indeed, a U-shaped curve has been observed when comparing accumulated endurance training and cardiovascular trouble, specifically atrial fibrillation (Scheer et al., 2021). Researchers tested the concentration of serum troponin, a marker of cardiac injury, in athletes, and found it to be the greatest immediately following a UER event, though changes were “temporary” and didn’t lead to “irreversible myocardial injury” (Malek et al., 2019). However, the restructuring of the heart was still observed in veteran UER competitors, possibly increasing their susceptibility to cardiac events. And though these cardiac events are rare, even among longtime UER athletes, the reshaping of the heart takes place without noticeable symptoms, happening gradually over a long period of time, and cardiac events and fatalities happen suddenly (Patil et al., 2012).
Yet the association between UER, the reshaping of the heart, and the subsequent risk of a cardiac event is not all so doom and gloom, at least according to more recent research. A 2020 study of an elite 36-year-old Polish UER athlete, who was tested 1-2 and 10-11 days after a victory at his country’s 24-hour national championship race, showed no “permanent adverse effects” on his heart, leading researchers to conclude that after “years of professional training,” adaptation had taken place (Gajda et al., 2020). Furthermore, and perhaps even more convincingly, the American Heart Association issued a statement in 2019 that, “extraordinary levels of physical activity” are not, in fact, directly associated with “greater risk of all-cause of cardiovascular disease mortality (American Heart Association, [AHA] 2019). However, it was acknowledged that “extreme joggers” can exhibit higher mortality levels, and the relationship between “very high volumes of long-term physical activity” and mortality is still questioned (AHA, 2019). Yet the results of this study are overwhelmingly positive, with no statistically significant results observed indicating a heightened cardiovascular mortality risk for UER athletes. A follow-up study from the Cooper Institute in Dallas indicated that, while athletes who trained at a high level did exhibit greater arterial calcification, this didn’t appear to impact risk of heart disease (DeFina et al., 2019). But not all professionals are so confident. In 2012, cardiologist Dr. James O’Keefe told Today that when the heart goes from pumping 5 quarts per minute (at rest) to 25 to 30 (while running), overstretching and muscle fiber damage are simply unavoidable. “The heart wasn’t meant to do that for hours, day in and day out,” (Carroll, 2012) he infamously said.
So, what’s a runner to do? In reviewing the literature, it is clear that the most recent studies are quite positive, indicating that, while UER does put a strain on the heart, as it certainly does the rest of the body, that stress isn’t necessarily indicative of an increased risk of cardiovascular troubles. However, previous studies cannot be ignored, and it is worth proceeding with caution. More research is needed on the long term effects of this emerging extreme sport, and athletes should take care to listen to their bodies, especially during strenuous events. It doesn’t take an expert to realize that UER is tough on the body. But is it a recipe for premature mortality and heart failure? In the words of American marathoning legend Amby Burfoot, “if you think you’ve got something, show me the bodies in the streets” (Burfoot, 2011). Until concrete evidence proves otherwise–and perhaps even if it does–endurance junkies will continue to plug away at dozens, hundreds, and thousands of miles, running with heart every step in more ways than one.
