Too much of anything — even a good thing — can be bad for you. Even exercise. Well, specifically high levels of intense exercise, which may be cardio-toxic and promote permanent structural changes in the heart.
According to a review published this week in the Canadian Journal of Cardiology, these disturbing findings can predispose some individuals to experience arrhythmias, or abnormal heart rhythm. The review explores current controversies and makes the case for investing in large prospective research studies into the effect of intense exercise on heart structure and function.
Don’t drop your workout routine just yet. Sitting on the couch and adopting a sedentary lifestyle is not the answer! The point of the review is to look at the association between long-term sports practice and increased prevalence of atrial fibrillation — and how it relates to chronic altered atrial substrate. The review doesn’t challenge the benefits of low- and moderate-intensity exercise. Rather, it takes a look at the available data for and against the concept that intense exercise, particularly endurance exercise, may cause adverse cardiac changes in some athletes.
"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 fueled an environment in which one may be criticized for even questioning the benefits of exercise," explains André La Gerche, MD, PhD, head of sports cardiology at the Baker IDI Heart and Diabetes Institute, Melbourne, 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."
As Dr. La Gerche points out, all available therapies, pharmacological or otherwise, have a dose-response relationship whereby benefits diminish at high doses and the risk of adverse events increases. An open mind would consider that this may even be possible for exercise, he suggests.
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. Dr. La Gerche excludes inherited conditions from this discussion, focusing instead on whether exercise may affect a change in the heart that may serve as a cause of arrhythmias in its own right. He reviews the following emerging controversies:
Many of these controversies are based on small cross-sectional cohort studies and small mechanistic studies that are dwarfed by the large population studies supporting the benefits of exercise, albeit in doses of exercise less than those commonly practiced by elite sportspersons, notes Dr. La Gerche.
"The answers regarding the healthfulness of 'extreme' exercise are not complete and there are valid questions being raised," continues Dr. La Gerche. "Given that this is a concern that affects such a large proportion 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."
While researchers continue looking into the ramifications of intense exercise on the heart, remember to take it easy, never overdo it, always listen to your body and make sure to stay on top of annual checkups.