Contrary to concerns raised by some cardiology experts, people who exercise an “extraordinary” number of hours per week are not damaging their hearts, according to a new report presented Monday at the annual meeting of the American Heart Association in Philadelphia.

 A group of Dallas-based researchers shared health and mortality data for 54 men and 12 women who regularly engaged in 35 hours per week of leisure-time physical activity. No one had previously investigated more than a handful of similar individuals.

Despite their unusual regimens, the extraordinary exercisers, who had an average age of 53, suffered no heart-related deaths in 10 years of follow-up. In addition, they differed in no significant way from a comparison group of 2,088 exercisers who reported about 1.5 hours a day of activity.

Americans have long been advised to exercise consistently. But beginning eight years ago, some cardiologists started warning about excessive endurance exercise. The Dallas study seems to counter those fears.

“Our findings tell avid exercisers that their habits don’t put them at an increased mortality risk,” says first author Laura F. DeFina, president of the Cooper Institute, where the data was gathered.

The extraordinary exercisers reported that they had been active for 26 to 28 years. While their total training in many ways mimicked that of Olympic distance runners, they appeared normal by many measures. They had an average BMI of 26.3, slightly into the “overweight” category that begins above 25, and an average total cholesterol of 196 mg/dl, barely below the 200 mark that is considered “borderline high.”

The researchers cannot say why the subjects exercised so much, as the question was not asked. “We can only infer that they were endurance exercisers who appeared to do a variety of exercise,” DeFina says. On a questionnaire, many noted their participation in running, bicycling, swimming and other exercise, mostly at an intensity equivalent to a very fast walk or a very slow jog — that is, effortful but not exhaustive.

“Some might have been training for an Ironman triathlon, some for multiple marathons, and many simply for optimal cardiovascular health over time,” says senior author Benjamin F. Levine, from UT Southwestern Medical Center and Texas Health Presbyterian Hospital in Dallas.

The 2018 “U.S. Physical Activity Guidelines for Americans” recommend 150 to 300 minutes per week of moderate exercise (such as walking), or 75 to 150 minutes per week of vigorous exercise (such as running), plus two days a week of strength training. The guidelines note that the benefits extend well beyond longevity to also include lower rates of cancer, high blood pressure, diabetes, depression, cognitive decline and serious falls in older individuals.

Beginning in 2011, however, a small group of physicians began to raise alarms about too much exercise. In a TED talk video viewed more than 1 million times, cardiologist James O’Keefe of Kansas City, Mo., spoke about “startling new insights that seem to be emerging about exercise.” A runner himself, O’Keefe continued: “I’m worried I might have made a lethal mistake.”

The next year, O’Keefe and colleagues wrote a paper that argued against more than 2.5 hours of running per week. By doing more, they claimed, runners might “substantially diminish the remarkable gains in longevity conferred by moderate jogging.” This contrarian claim — which I challenged at the time — made headlines for the same reason that a single runner death in a marathon attracts more attention than 25,000 successful finishers. However, it has never been confirmed by well-conducted epidemiological research with a sizable sample of heavy exercisers.

Meanwhile, papers have shown that Tour de France riders live longer than noncompetitors, and that those who complete a famous 56-mile cross-country ski race (the Vasaloppet) in Sweden likewise outlive controls. More importantly, large-data meta-analyses and systematic reviews have confirmed the benefits, or at least the lack of harms, accrued by serious exercisers.

Just three months ago, the British Journal of Sports Medicine published a report pulling results from 48 papers on exercise and health outcomes. It concluded: “Mortality risk was lower at physical activity levels well above the recommended target range. Further, there was no threshold beyond which lifespan was compromised.”

Levine is no exercise zealot. Like most fitness advocates, he’s primarily interested in getting more people to begin moving more and sitting less. But he also believes in supporting those who are passionate about their serious exercise regimens.

“Our paper, based on far more data than previous papers, is essential to counter the idea that the streets are littered with the bodies of dead runners,” he notes. “We studied the most strenuous exercisers ever, and there were no heart deaths in 10 years of follow-up.”

For those seeking a less-extreme program, Levine offers this 3- to 3.5-hour weekly “exercise prescription for life,” based on his decades of reviewing exercise and health research. On one day, do an hour of something active and fun. On another day, do an interval workout that includes four minutes at high intensity, followed by three minutes of recovery. Repeat four times for a total of 28 minutes. On two or three days, do 30 minutes of moderate aerobic activity. On any day, do 30 minutes of strength training.

 Levine also cautions: “Exercise is not magic, particularly not for those trying to overcome a lifetime of bad habits. Even high-volume exercisers who are strong and fit are vulnerable. Anyone who develops symptoms while training should consult their doctor.”

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.”

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