February 26, 2016 2:38 pm

Reality check: Is intense exercise ‘toxic’ for your heart? Here’s why Canadian docs say no

Athletes run during the women's marathon at the Pan Am Games in Toronto, Ontario, Saturday, July 18, 2015.

AP Photo/Felipe Dana

You train for marathons, swim laps at the pool and cross-country ski for hours. While working out is good for your health, an alarming new study is warning that high levels of intense may be “cardiotoxic.”

Australian researchers warn that endurance athletes may be altering the structure of their hearts, leaving them at risk of irregular heartbeat.

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But Canadian experts are hoping these findings won’t dissuade people from working out – the risk is specifically for elite athletes who spend hours of their days and years of their lives pushing their physical boundaries with training.

Headlines circulated: “Intense exercise can be bad for heart,” “Could too much exercise be toxic?” and “Too much of intense exercise unhealthy for the heart.”

But don’t give up your gym membership and hang up your cross-country trainers yet. Global News looks at the study’s findings and the verdict from Canadian experts.

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The study’s findings: For their research, sports cardiologists out of Melbourne reviewed studies that zero in on long-term sports training and risk of atrial fibrillation, which is when you have an irregular heart rhythm.

The scientists made sure they left out people who were already predisposed to heart conditions because of their family history, for example. They note that heart attacks in athletes are typically tied to underlying issues, but they wonder if structural changes to the heart from over-exercising could be the culprit.

Research has suggested that marathon running increases cardio risk by seven times. Other findings point to marathon running scarring heart muscles. But it’d take about 100 or more marathons for the damage to set in.

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The Australian doctors say that there are “unquestionable benefits” for getting off the couch and getting active. But they suggest the medical community and the media have shied away from looking at how too much exercise could be bad for your health out of fear of being “criticized for even questioning the benefits of exercise.”

Sound bite: “The answers regarding the healthfulness of ‘extreme’ exercise are not complete and there are valid questions being raised,” lead researcher, Dr. Andre La Gerche, said in a press release.

“Given that this is a concern that affects such a large population of society, it is something that deserves investment. The lack of large prospective studies of persons engaged in high-volume and high-intensity exercise represents the biggest deficiency in the literature to date, and although such work presents a logistical and financial challenge, many questions will remain controversies until such data emerge,” he said.

The counter-arguments: Doctors want those who love to work out to know that the study is zeroing in on elite top-performing athletes, not everyday Canadians who go to the gym daily for cardio, weights and other training.

Sound bite: “We’re not really talking about people who engage in marathons, triathlons, things about that sort. Many, many hours of very intense training and endurance,” Dr. Nesochi Igbokwe, of New York University’s Languone Medical Center, told U.S. outlets.

“We’re not talking about people who are working out two or three times a week for an hour or two,” Igbokwe said.

Canadian experts weigh in: The findings are accurate, according to Dr. Mark Tarnopolsky, a researcher at McMaster University Medical Centre, and Dr. Jack Goodman, a kinesiology professor at the University of Toronto.

Top sport endurance athletes have an increased risk for both atrial fibrillation and atrial flutter, but this applies only to a small segment of the population dedicated to elite, long-term training.

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“These are people who are training for hours a day, doing 30-kilometre trail runs, adventure racing, cross-country skiing. These folks when they get into their 50s, you start to see the increased risk of [arrhythmia],” Tarnopolsy said.

With atrial fibrillation, the electrical signal isn’t synchronized throwing off the rhythm of your heartbeat. You end up feeling short of breath, light-headed and lethargic.

It’s unclear why endurance exercise tampers with the heart. Doctors say the stress on the heart muscles could cause scarring.

“It’s this interaction between chronic and endurance exercise training superimposed on the normal aging effects on the heart. That’s why we see it coming out after years in their 30s, 40s and 50s,” Tarnopolsky said.

Atrial fibrillation affects about 350,000 Canadians, according to the Heart and Stroke Foundation. It increases an average person’s risk of stroke by three to five times.

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But keep in mind, there are so many benefits tied to exercise and a healthy lifestyle, Goodman says. It could be that long-term exercise habits cancel out any negative repercussions on your heart from working out.

He’s had to reassure patients that they should continue training for marathons, for example. Research could be taken out of context and turned into a “gross exaggeration,” he worries.

“The vast majority of people who exercise have a lower risk of heart disease, they’re healthy and they tend to live longer. To make a global statement that exercise is bad for your heart is unfounded and isn’t based on strong evidence,” he cautioned.

“The bottom line is it’s much more dangerous to be sedentary than it is to exercise,” Goodman said.


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