The past year, 2006, wasn't a good one for marathoners who believe that running improves their heart health. In fact, it might have been the worst since 1984, when Jim Fixx died of a heart attack while running in Vermont. At least 6 heart-related deaths occurred in U.S. marathons last year, and several research studies conducted at the Boston Marathon seemed to indicate that marathon running could harm the heart.
However, that's not the correct interpretation of those studies, says cardiologist Malissa J. Wood, M.D., the head researcher and a 4-time marathoner herself. In fact, Wood believes strongly in the health benefits of vigorous exercise. She merely cautions that marathoners should train seriously for the 26.2-mile distance before attempting it.
Two of Wood's Boston Marathon studies have been published in highly respected medical journals in the last 6 months, one in the European Heart Journal and the other in Circulation: Journal Of The American Heart Association. The first found that the marathoners' hearts had temporarily depressed pumping and relaxation efficiencies after the marathons. The second found that their hearts leaked proteins that indicate cardiac cell injury.
The studies sounded bad, and that's the way they were generally reported in the press, particularly a December article in the New York Times that lumped Wood's studies together with reports of the six marathoner deaths during 2006. However, Wood, co-director of the Women's Health Heart Center at Massachusetts General Hospital and an instructor at Harvard Medical School, begs to differ.
"The first study showed no evidence of long-term harm to the heart," she said in a Runner's World interview in early 2007. "Six weeks after the marathon, the runners hearts were pumping in a completely normal, healthy manner. Their heart relaxation phase was still lower that before the marathon, but I really, really think this resulted from the decreased training they did after the marathon."
The results of the second study, she added, "have no relationship to reports of heart attacks or sudden deaths among runners. The runners we saw in the Boston Marathon medical tent had no health problems and required no medical attention. But many of them showed evidence of heart fatigue or energy delivery problems. Their cell membranes leaked troponin, which is what cardiac muscle does when it is stressed."
According to Wood, other studies have shown that the healthy heart quickly repairs these cell membranes, stems the troponin leakage, and suffers no permanent damage. She likened the troponin leakage to the leg muscle pain runners feel when they increase their training mileage. At first, there's considerable soreness. With more training, however, the muscles get stronger and the soreness diminishes.
Nearly the exact same thing happened in the her troponin study. The Boston marathoners who had trained on less than 35 miles a week exhibited nine times the troponin leakage as those who trained over 45 miles a week. In fact, the latter group had almost no troponin leakage, according to the report in Circulation. It commented, regarding this group's troponin levels: "No appreciable change from baseline was noted."
Wood is a cardiologist specializing in echocardiography who sounds a lot like a marathon coach. Her training philosophy is clear and similar to what many runners have heard before, only this time it's coming from someone far more interested in heart health than in fast performances. "When runners are doing 45 miles a week or more, that means they're usually getting in a weekly long run of 15 or 18 or 20 miles," she notes. "They're not just running 6 miles-6 miles-6 miles every day. And I think it's the long runs that give the heart exposure to the kind of prolonged, continuous stress it needs to deal effectively with the marathon."
Of course, your training does affect your performance. In Wood's Circulation study, based on the 2004 and 2005 Boston Marathons, she divided her subjects into those who had trained <35 miles a week for 4 months, from 35 to 45, and >45 miles a week. In addition to the different troponin levels in their blood, they had different average finish times: 4:28, 4:05, and 3:45 respectively.
With more and more people getting interested in marathons, including those who don't have a long athletic history, Wood sees a public health message to her findings. She thinks it's fine for veteran runners with consistent training programs to continue entering marathons without giving any special thought to potential heart risks. But new runners, and the overweight, and those who have lost a lot of training time, and those making a comeback, and those with warning signals like high blood pressure or diabetes–they should first check in with their physicians. At the very least, they should build up their training slowly, gradually, and sufficiently to the marathon challenge. It is, after all, a challenge, to the heart as well as the mind.
Wood, who has a marathon PR of 3:40 and still runs 40 miles a week at age 46 with four children and a demanding career, listened to her own advice last fall. She was running strongly after the birth of her fourth child, and felt ready to get a Boston Marathon qualifier in the LaSalle Bank Chicago Marathon. Then, in late September, she received an unexpected invitation to China, where she spent several weeks at 15,000 feet without time for any training. "It was stressful, and I didn't do any running, and I wasn't in my best physical shape when I returned," she said. "I could have run Chicago, but I thought I ought to listen to my own message and practice what I preach. I can always get a Boston qualifier this year."
Or the year after, or the one after that, or maybe in the next decade or two. "Unless something comes along to stop me, I expect to be running until I'm 75," said Wood. "When you look at as many echocardiograms as I do, you get to really appreciate the youthful appearance patterns of the echos of the 70-year-olds who are regular exercisers. They look as good as most people in their 40s."
The benefits of exercise can extend all the way to the marathon distance. At the end of their paper in Circulation, Wood and coauthors stressed the importance of "appropriate preparation" (ie, training) for those interested in endurance activities like the marathon. With this training, they concluded: "There are no data to suggest that there are long-term sequelae to the increase in biomarkers and echocardiographic evidence of injury in this setting. In contrast, many studies suggest that endurance exercise is associated with a reduction in cardiovascular risk and an increased life expectancy."
Wood and colleagues were able to perform their research thanks to the recent invention of lightweight, portable tissue Doppler echocardiogram units. Earlier echo machines weighed 800 pounds apiece, not exactly great for moving them to a marathon finish line. And prior to the tissue Doppler machines, which can "see" actual cardiac muscle contraction and relaxation, earlier units could only image blood flow through the heart. Technicians had to use the blood flows to make assumptions about cardiac muscle function.
Wood's research, which has been conducted at the last 4 Boston Marathons and is scheduled to continue, also required the full cooperation of the Boston Athletic Association organizers and the runners who volunteered to be studied, about 30 a year. That was all the investigators could handle efficiently. Wood was most impressed that her team was able to identify their subjects in the finish-line chutes and guide them into the medical tent. "In the big crowds and chaos of a marathon finish area, you'd expect to lose some people," she said. "Or maybe they wouldn't finish. But we've been extremely lucky with both the marathon organizers and our subjects."
Persistent and reversible cardiac dysfunction among amateur marathon runners. (European Heart Journal, May 06)
Myocardial injury and ventricular dysfunction related to training levels among nonelite participants in the Boston marathon. (Circulation, Nov. 06)