October 29, 2010 (Montreal, Quebec City) — Running 26.2 miles takes its toll on even the most physically fit athletes, but new research reveals that the ultimate endurance event is most detrimental to the hearts of runners with less aerobic endurance. Investigators showed that less fit runners, assessed by VO2max testing, had signs of inflammation, swelling, and decreased perfusion assessed by MRI three months following the race, while those who were better trained were less likely to experience such damage.
"This is an observational study, and what we observed was that the lower the fitness levels, the more cardiac injury after the run," lead investigator Dr Eric Larose (University of Laval, Quebec City) told heartwire . "When you train somebody, you increase their fitness levels, and you decrease the amount of harm done."
The good news, said Larose, who presented the results of the study during the Canadian Cardiovascular Congress 2010, is that even those less physically fit runners who showed signs of cardiac distress bounced back three months after the race. "The damage that we're seeing does seem to be temporary and reversible," he said.
Apparently Healthy But Drops Dead During a Race
Speaking with heartwire , Larose said that regular exercise significantly reduces the risk of cardiovascular events two- to threefold, but during exercise that risk actually increases, "something most people have a hard time wrapping their heads around." Over the long haul, however, the benefits of exercising far outweigh the short-term risks.
The purpose of the study was to assess any physiologic changes that occurred over the course of 26.2 miles. Larose explained that he had his scientific curiosity piqued in 2001 when, while he was still out on the course of a marathon he was running, an individual collapsed near the finish and was unable to be resuscitated. As a cardiology resident at the time, Larose said he started looking into deaths occurring during the marathon and was surprised to discover it was a "fairly common event," and while some deaths were attributed to structural abnormalities of the heart or to underlying coronary disease, the cause of death was unknown in many individuals.
"We wanted to know why somebody who is apparently healthy and is running a marathon can suddenly drop dead," said Larose.
Larose and colleagues reached out to a number of running clubs in Quebec, eventually including 20 amateur runners of varying running experience, including one veteran of 30 marathons, in an MRI study designed to examine their hearts six to eight weeks prior to the race and two days and three months after the event. In addition, all individuals underwent VO2max testing in order to determine their level of fitness prior to the race. The average age of individuals in the study was 45 years, and 70% were male. All were considered healthy, with "normal" hearts at baseline assessed by MRI, as well as by VO2.
Results of the MRI examination at three months showed that there was no permanent necrosis observed in the runners. There was, however, injury to the heart observed in the two days following the race. The MRI showed an increase in inflammation and swelling and decreased perfusion in segments of the left ventricle. Larose explained that the left ventricle when screened by MRI is divided into 17 segments, as recommended by the American College of Cardiology (ACC)/American Heart Association (AHA), and 53% of these segments had decreased function immediately after the marathon. As a result, the other segments of the ventricle are forced to work harder, he said.
"When we see this, we consider it a sign of trouble," Larose told heartwire . "Inflammation can be associated with arrhythmia and other cardiac events."
As noted, the fitter runners, those with a VO2max that exceeded 50 L/min in this trial (although Larose stressed this was not a predefined threshold and is not meant to be a goal for runners), had less damage to the left ventricle. The runner with the best aerobic endurance had no segmental dysfunction, while the less fit runners, those with lower VO2max scores, were more likely to have some damage to the heart.
The bottom line is that clinicians shouldn't assume there is no cardiac risk involved in individuals who run the epic 26.2 miles. "To sweep this under the rug and say, they're marathoners, they're good, is not okay," said Larose.
Larose said that future prospective studies will need to address whether endurance training designed to increase VO2max reduces the amount of segmental damage to the left ventricle. It is unclear whether the damage observed is simply an adaptive response to the marathon, although there are no current data suggesting that it is. The data, he added, are preliminary, so it is too soon to make any recommendations on who should run a marathon or who might end up with cardiac damage.
Heartwire from Medscape © 2010 Medscape, LLC
Cite this: Marathon Running Hardest on the Hearts of Those Less Physically Fit - Medscape - Oct 29, 2010.