Study bolsters findings that marathons increase heart stress. But what that means is unclear

By | December 4, 2018

A new “Research Letter” published Dec. 3 in the American Heart Association’s journal Circulation raises the old fear that running long distances – particularly the 42.2-kilometre marathon – could be bad for amateur runners. But according to several experts, including the paper’s author, would-be marathoners should not worry that they are on the road to a heart attack or heart disease, though it is smart not to attempt the marathon distance until you have trained sufficiently.

A group of Spanish physiologists reported that “the strain imposed on the myocardium by competing a full marathon is much greater compared with other distances such as the half-marathon or 10-km races.” They came to that conclusion by measuring the same proteins in runners’ blood that doctors look at to diagnose heart attacks. The biomarkers – cardiac troponins – were elevated in all 63 runners (39 women and 24 men, with an average age of 37) after completing their races, but particularly so among the marathon runners.

But the Spanish team made no claims about heart attack or heart disease risks among the marathon runners. Indeed, the Letter notes that “the release of cardiac troponins after exercise may not be indicative of any cardiovascular dysfunction.”

This is precisely the finding of other studies published over the last decade, including a handful in Circulation, a scientific journal published for the American Heart Association. “I don’t see anything new here, and the increased likelihood of a troponin bump with marathon vs. shorter distances has been well described before,” Malissa Wood, of Boston’s Massachusetts General Hospital, told me by email.

Support for the benefits of regular, even intense, aerobic exercise remains as strong as ever

Wood was a co-author of the first major paper on the subject, which appeared in Circulation in 2006. That investigation followed 60 nonelite participants in the 2004 and 2005 Boston Marathons. All had unmeasurable troponin before the marathon, but more than 60 percent had levels greater than 99 percent of normal post marathon. Still, the paper concluded: “There are no data to suggest that there are long-term sequelae to the increase in biomarkers.” In other words, no subsequent heart damage.

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Paul Thompson, chief of cardiology at Hartford Hospital in Connecticut, Paul Thompson, has been researching the exercise-heart connection for 40 years, including work with Wood and others on cardiac troponins. “We’ve long known that troponins increase after exercise,” he said in an email. “The new Research Letter’s small contribution is to suggest that long-term effects should be studied. We all agree with this, and lots of groups, including ours in Hartford, are already doing this.”

In 2010, a team of internationally known exercise cardiologists, including Wood and Thompson, collaborated on a “State-of-the-Art Paper” for the Journal of the American College of Cardiology. The authors noted the explosion in exercise-and-troponin papers “due to the development of highly specific cardiac troponin assays coupled with theoretical concern about the cardiovascular safety of prolonged exercise.” Yet they concluded: “Because most of these data involve healthy individuals with no underlying cardiovascular disease, it seems likely that exercise-induced cardiac troponin release is a benign process.”

In 2014, a systematic review of “High-sensitivity troponin after running” reached a similar finding. The authors could locate no “pathological studies” linking post-exercise troponins to clinical heart illness. A 2012 paper in the Journal of Applied Physiology had demonstrated that 14-year-old cross-country runners also developed high troponin readings after a 90-minute treadmill workout. But the teens had no adverse clinical symptoms, continued racing for their youth teams, and clearly represented a group with little to no coronary risk.

A 2012 paper in the Journal of Applied Physiology had demonstrated that 14-year-old cross-country runners also developed high troponin readings after a 90-minute treadmill workout

The Spanish team has been studying marathoners since 2011, according to lead researcher Juan Del Coso, from Madrid’s Universidad Camilo José Cela. When they noticed many runners walking in the final miles, they wondered about the runner’s training programs for the event. The researchers first studied skeletal muscle strain among runners and found that those who trained less produced more markers of muscle damage. This led them to wonder about heart muscle damage, which produced the Research Letter results.

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“I do not think the increased cardiac strain is going to produce a heart problem per se,” Del Coso wrote in an email. “If you’ve prepared correctly, which includes training, nutrition, and hydration strategies, then there is no reason to stop running marathons.”

However, Del Coso believes less-well-prepared amateurs should be more cautious when picking a race distance. “If you began training only a few months back, of if your busy life impeded your training, you should choose shorter races.”

Average marathon times have slowed dramatically in recent decades compared with the 1970s and 1980s, as slower – and presumably less-well-trained – runners have flocked to the marathon. However, there appears to have been no associated increase in marathon death rates, according to Bill Roberts, a physician who compiles such rates for the Twin Cities and Marine Corps marathons. (Amazing marathon stat: November’s New York City Marathon, with more than 50,000 starters from around the world, had a 99.8 percent finish rate.)

Meanwhile, support for the benefits of regular, even intense, aerobic exercise remains as strong as ever. A month-old Cleveland Clinic paper tracked the mortality rates of 122,000 patients for a median 8.4 years after they had undergone treadmill stress testing. Subjects at the highest level of fitness, termed “elites,” had an 80 percent lower risk of death than the lowest, most sedentary subjects. The elites, with aerobic capacities roughly equivalent to a 21-minute 5K race (or 3:20 marathon) even fared 23 percent better than the next-highest group.

“Current endurance athletes should not be worried,” said Hartford’s Paul Thompson. “They always live longer than their sedentary peers, and there remains no conclusive evidence that their exercise is dangerous.”

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Amby Burfoot is a freelance writer and editor and a member of the Running Hall of Fame. His most recent book is Run Forever: Your Complete Guide to Healthy Lifetime Running.

Health – National Post