Marathoner's Heart: Functional and Structural Adaptations After Just 18 Weeks

February 13, 2015

BOSTON, MA — A new study suggests that marathon training is perfectly safe for middle-aged adults and that engaging in a structured training program translates into significant and healthy improvements in the heart's size and function[1].

After an 18-week training program that culminated in running the 2013 Boston Marathon, a group of men, some of whom had limited marathon experience, showed positive functional adaptations and structural remodeling in addition to improvements in exercise capacity and reductions in total-cholesterol, LDL-cholesterol, and triglyceride levels. The results, say investigators, suggest non-elite, recreational runners adhering to a standard training program undergo the same functional and structural changes that have previously been shown in elite competitors.

"We know from lots of studies of elite athletes that athletes develop remodeling," senior investigator Dr Aaron Baggish (Massachusetts General Hospital, Boston, MA) told heartwire . "Their hearts get bigger, they get more efficient. Now for the first time we're seeing that these changes—which are adaptive and healthy—can occur in average, recreational exercisers. That's what so exciting about it. These weren't Olympic athletes. They were middle-of-the-pack marathoners who ended up showing the same positive, healthy changes with 18 weeks of training."

The bottom line," said Baggish, "is that individuals who are interested in participating in the marathon at a recreational level should have absolutely no health concerns around it." Everything about the study, he added, "suggests they are going to make themselves healthier."

Your Average Marathon Runner

The study, which is now published in the February 2015 issue of Circulation: Cardiovascular Imaging, included 45 men who ran the 2013 Boston Marathon as part of the Dana Farber Marathon Challenge. The runners adhered to the 18-week training program, running four to five times per week (6 to 13 km), with one day devoted to a longer run that increased in distance over the course of the program (maximum distance 32 to 34 km at week 15). In the 2 months prior to starting the program, the runners ran approximately 22 km per week.

The men were recruited for the study because as charity runners they are more representative of middle-aged recreational runners than the typical Boston marathoner who qualifies for the event based on time, say the researchers. Approximately half the men had run more than five previous marathons (experienced cohort), while the other half had completed five or fewer marathon races. The experienced cohort were older, shorter, weighed less, and drank more alcohol than the less experienced group.

Compared with baseline testing, marathon training was associated with a significant increase in the size of the left ventricle (LV) measured by end-diastolic volume, end-systolic volume, and LV mass index. There was also a significant increase in the right ventricle (RV) size and left atrial volume. LV diastolic function, as assessed by early and late diastolic relaxation velocities, was also improved after marathon training.

"Everything really looked very, very good," said Baggish. "It's interesting, too, because seven of them actually had overt diastolic impairment before they started training. Their hearts just weren't relaxing efficiently. But this was just completely erased with training. All of them had normalized. I think one of the most important functional changes that we saw from a public-health perspective is that improvement in diastolic function. That underlies why exercise is really good for people in the second half of life."

There was no difference in the functional or structural changes between the experienced and less experienced marathon runners. In terms of physiological changes, all runners showed improvements in maximal exercise capacity and submaximal exercise performance, as well as reductions in cholesterol and triglycerides. HDL cholesterol was not affected with training.

"No matter which risk factor we looked at, marathon training made it better or didn't change it," said Baggish. "It makes it hard to implicate running as a cause of heart problems."

In an editorial[2], Drs Stefan Möhlenkamp (Bethanien Hospital, Moers, Germany) and Martin Halle (Technical University, Munich, Germany) say the study shows that the myocardial adaptation to high-volume aerobic exercise training can occur in as little as 4 to 6 months, even among recreational athletes with cardiovascular risk factors. In the trial, 64% of the runners had at least one cardiovascular disease risk factor, they note.

As for marathon running for the prevention of cardiovascular disease, the editorialists write that data from their own cohort of recreational runners have shown that despite a lower risk-factor burden than age-matched controls, individuals who ran marathons had a greater burden of coronary artery calcification. In addition, myocardial fibrosis has been observed in some marathoners. "These data cast a shadow of uncertainty on the health benefits of regular marathon training and competition, especially in persons with prevalent but unknown cardiovascular disease," they write.

Baggish, however, disagrees. "I think our study shows that [running a marathon] is extremely safe and that the type of marathon training most people do—20 to 30 miles to get ready for a run—improves health across the board."

Running and its benefits recently attracted a lot of media attention in the past couple of weeks, including a story by heartwire , when an analysis suggested the largest mortality benefits were observed among individuals who jogged easily, less frequently, and for shorter periods of time.

The authors and editorialists report no relevant financial relationships.

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