There are unquestionable benefits to "getting off the couch." 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.
Without challenging the undeniable evidence supporting low and moderate intensity exercise, the review published in the Canadian Journal of Cardiology by sports cardiologist André La Gerche, MD, PhD, provides a balanced discussion of the available data for and against the concept that intense exercise, particularly endurance exercise, may cause adverse cardiac changes in some athletes.
The paper conclude that there is growing evidence that high levels of intense exercise may be cardiotoxic and promote permanent structural changes in the heart, which can, in some individuals, predispose them to experience arrhythmias (abnormal heart rhythm).
"The answers regarding the healthfulness of 'extreme' exercise are not complete and there are valid questions being raised," says the author. "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 emege."