Why marathons are bad for you

Running or even just walking a modest amount a few times each week was still associated with solid health benefits. There does seem to be a point of diminishing returns with exercise. Many marathoners, however, are not running Cancer survivor Ethan Zohn has competed in four marathons and one ultra-marathon.

He says he runs to be a part of something bigger than himself. It was a way to get myself back to health after cancer. I started by walking half a mile, then moved on to jog half a mile, then run a few miles. Meeting daily goals helped me build my strength back. Zohn also runs on behalf of GrassRootsSoccer , a charity he co-founded. Studies have shown that people who volunteer to help others are happier, have greater self-esteem, less depression and lower stress levels than those who don't.

Marathons are massive events that attract millions of people throughout the world. But he stopped in , after he said research showing the potential dangers made them not worth the risk. He'd like to see more research, such as a widespread registry of athletes involved in endurance sports and eventually a clinical trial that includes MRI results.

McCullough was part of the study that used MRIs to identify the long-distance runners whose right atrium and ventricle dilated immediately after a marathon and up to 24 hours later. It also included blood tests that showed an elevation in biomarkers that are indicators of heart stress and injury. A smaller subset, he estimates about 1 percent, could be prone to scarring. Myocardial fibrosis, or scarring of the heart, can lead to heart failure.

A study published in on triathletes showed that 18 percent of the male participants, those who trained and competed the most, had more heart scarring than the other athletes. Meyer, who has finished 16 marathons tries to keep a daily running streak going, even if it's a few miles a day. He said federal guidelines of at least minutes of moderate-intensity exercise a week or at least 75 minutes at a vigorous intensity "are reasonable and promote heart health for the long-term.

He pointed to a Stanford University study published in that focused on runners and non-runners in their 50s. Researchers tracked them for more than two decades.

At the beginning of the study, the runners ran an average of about four hours a week. After 21 years, their running time declined to an average of 76 minutes a week, but they were still seeing health benefits.

Nineteen years into the study, 34 percent of non-runners had died compared with 15 percent of runners. David Sabgir, a cardiologist with Mount Carmel Health Systems in Columbus, Ohio, said he doesn't want studies that apply to one segment of hardcore long-distance runners to dissuade others from getting into exercise.

Over the decade, 59 of the runners had a cardiac arrest - where the heart stops working - and 42 of these people died. Dr David Oxborough, who has studied how marathons affect the heart, says when deaths during marathons do happen they tend to occur in people who had undiagnosed heart problems, either in older people or in those with inherited conditions.

While these deaths are rare, Dr Oxborough says they underscore why it is important for people to get a health check-up from a doctor before doing a marathon. While marathons are a big challenge for our bodies, ultimately any of the health risks are more than outweighed by the benefits, experts say. But experts say the key, particularly for inexperienced runners, is to not do too much too soon, follow a good training plan, and "listen to your body".

Sophie Everett has not run since her first and last marathon because of the ongoing pain in her feet, but Barry Trott has since gone on to complete several marathons.

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