Marathon running puts heart under strain, say researchers, who urge sufficient training
- Strain imposed by running 42km race is much greater than when running shorter distances, Spanish study shows
- Researchers find no evidence of increased risk of heart attack or heart disease, but say runners should make sure they train enough for the longer distance
A new “Research Letter” published in the American Heart Association’s journal Circulation raises the old fear that running long distances – particularly the 42.19km 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.
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A group of Spanish physiologists reported that “the strain imposed on the myocardium by competing in a full marathon is much greater compared with other distances such as the half-marathon or 10km 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 versus shorter distances has been well described before,” Malissa Wood of Boston’s Massachusetts General Hospital, said.
Wood was a co-author of the first major paper on the subject, which appeared in Circulation in 2006. That investigation followed 60 non-elite participants in the 2004 and 2005 Boston Marathons.
All had unmeasurable troponin before the marathon, but more than 60 per cent had levels greater than 99 per cent of normal post marathon. Still, the paper concluded that there was no data to suggest that there was subsequent heart damage following the increase in biomarkers.
Paul Thompson, chief of cardiology at Hartford Hospital in Connecticut, 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.
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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 shown 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.
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 programmes 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.
“I do not think the increased cardiac strain is going to produce a heart problem per se,” Del Coso said. “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, or 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 doctor 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 per cent 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 per cent 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 per cent better than the next-highest group.
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“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.”
