Is too much exercise bad for the heart?

High levels of intense exercise may be cardiotoxic and may promote permanent structural changes in the heart, which can predispose some people to experience abnormal heart rhythm, a new study has claimed.
There are unquestionable benefits to "getting off the couch," researchers said.
However, there is already fairly compelling evidence supporting the association between long-term sports practice and increased prevalence of atrial fibrillation, and the fact that this relates to chronic altered atrial substrate.
"Much of the discussion regarding the relative risks and benefits of long-term endurance sports training is hijacked by definitive media-grabbing statements, which has fuelled an environment in which one may be criticised for even questioning the benefits of exercise," said Andre La Gerche from the Baker IDI Heart and Diabetes Institute in Australia.

"This paper discusses the often questionable, incomplete, and controversial science behind the emerging concern that high levels of intense exercise may be associated with some adverse health effects," La Gerche said.
All available therapies, pharmacological or otherwise, have a dose-response relationship whereby benefits diminish at high doses and the risk of adverse events increases, he said.

A commonly held view is that adverse clinical events in athletes are explained by exercise acting as a trigger in individuals who are susceptible because of an underlying abnormality.
La Gerche focused on whether exercise may affect a change in the heart that may serve as a cause of arrhythmias - abnormal heart rhythm.

"The answers regarding the healthfulness of 'extreme' exercise are not complete and there are valid questions being raised," said La Gerche.
"Given that this is a concern that affects such a large proportion of society, it is something that deserves investment," he said.
"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 study was published in the Canadian Journal of Cardiology.