By Linda Carroll

(Reuters Health) – Exercise, like most things in life, is good in moderation for most people, but extremes can hurt the heart, experts caution in a scientific statement from the American Heart Association.

While promoting regular exercise, the statement published in Circulation warns against extreme endurance sports and against couch potatoes trying to get fit too quickly.

“In many respects exercise is like medicine,” said lead author Barry A. Franklin, director of preventive cardiology and cardiac rehabilitation at Beaumont Health in Royal Oak, Michigan. “Like medicines, exercise comes with indications and contraindications. And overdosing and under-dosing are both possible.”

For most Americans, the issue is under-dosing, Franklin said.

But there are also issues with overdosing on exercise. Studies in ultra-endurance athletes show extreme exercise can result in scarring of heart muscle, irregular heart rhythms and build-up of coronary calcium, which can contribute to atherosclerosis, Franklin said.

“More and more people are engaging in extreme exercise because they think if some exercise is good, more is better,” he said. “That is not necessarily the case.”

It’s not just endurance athletes who risk damaging their hearts.

“The biggest risk is with people who have been inactive for years, such as the person who may have been a track athlete 40 years earlier and wants to start up again, running around the block,” Franklin said. “A major take home message is that anybody middle aged or older should start with a walking program and should not start with running. But most can start a walking program without a stress test.”

Start slowly, in the range of 2 to 3 miles per hour, Franklin said. “Then you can move up to 3.5 to 4 mph and if you’re on a treadmill you can increase the grade, provided you experience no symptoms,” he said. “But, if you develop pain or discomfort anywhere from the belly on up, it could be (a sign of angina) related to a blockage of one or more arteries.”

People starting to exercise should consult their doctors if they experience left arm, neck or jaw pain, an unusual, extreme shortness of breath, dizziness, or heart palpitations. “These all signify that something is wrong,” Franklin said, adding that most people who suffer a heart attack or cardiac arrest had symptoms in the preceding weeks and ignored them.

After reviewing more than 300 studies, Franklin’s team concluded that physically active people, such as regular walkers, had a 50% lower risk of heart attack and cardiac arrest. On the other hand, they found, while the risk of heart attack and cardiac arrest was low overall among participants in marathons and triathlons, it rises over time.

The important message is that regular exercise, that is, 30 minutes a day five days a week, is beneficial, said Dr. Annapoorna Kini, director of the cardiac catheterization lab at Mount Sinai Hospital in New York City, who wasn’t involved in the scientific statement.

Kini advises people who are thinking about exercising to choose something they’ll enjoy, whether it’s biking, working out on a treadmill, dancing or Zumba. “It’s got to be something you look forward to,” she said. “And you have to put some effort into weight training as you get older. After age 40 you start losing muscle mass.”

Kerry Stewart, who studies exercise physiology at Johns Hopkins University School of Medicine in Baltimore, said there’s a point beyond which health benefits don’t continue to increase with increasing time spent exercising.

In fact, benefits begin to decline past a certain point, said Stewart, who wasn’t involved in the statement.

SOURCE: Circulation, online February 26, 2020.