Running, Fitness and AF

I had thought about posting this in the General Discussion part of AF but have to think about it a bit more.
A while back there was a discussion and an article about the detrimental effects of long endurance high intensity exercise on the heart.  The article was from the Journal of the American College of Cardiology.  I've been reading some articles on this subject from the American Running Association, the non-medical newsletter for the public by the American Medical Athletic Association.A recent article in their newsletter, Running and Fit News (Jan/Feb 2015), summarizes conclusions from two large scale studies.  One was a study of "some 55,000 adults over 15 years—reported that runners (vs. non-runners) had 30% and 45% lower risks of all-cause and cardiovascular mortality, respectively, with a mean improvement in life expectancy of three years. Maximal benefit from running was not at the highest speeds or training volume, but the difference between the moderate and highest levels was close, and far less than the difference between sedentary and active."  "In another recent large analysis published in the Annals of Internal Medicine, researchers examined data from 47 studies that assessed the health effects of sedentary behavior adjusted for physical activity. Increased exercise blunted — but did not completely eliminate — the excess risks associated with sedentary behavior.""Given that this study found the ill effects of sedentarism will not be completely offset by even vigorous exercise, it seems doubly irresponsible for the media to suggest that vigorous exercise is no better than no jogging at all. Compare that with the Copenhagen study authors' original conclusion:“The findings suggest a U-shaped association between all-cause mortality and dose of jogging as calibrated by pace, quantity, and frequency of jogging. Light and moderate joggers have lower mortality than sedentary nonjoggers, whereas strenuous joggers have a mortality rate not statistically different from that of the sedentary group.” Nowhere is causation implied. "Finally, they had a word about the original study.  "As an observational study and not a randomized one, associations, not causes, are all that can be pointed out. The study authors do not actually imply that hard running increases mortality risk. And they acknowledge that the number of hard runners in the study was quite small: just 80 men and women. Any statistical information about death rates in this group must be viewed very cautiously.""Even more importantly, the researchers did not determine how and why the runners and non-runners had died. This makes it impossible to draw conclusions about what negative effects hard exercise might have on people. Combined with the decidedly vague definition of slow, medium and fast self-reported running, the study is a bit of a non-starter for uncovering useful relationships between running intensity and various health benefits."And this article from Medscape - http://www.medscape.com/viewarticle/844230?src=wnl_edit_tpal&uac=150732BNIt is a study saying that there is an inverse relationship between cardiorespiratory fitness and AF.  The study had 64,000 adults followed over a period of 5 years.  Their study concluded in part that even very high fitness levels were not associated with AF.  All of this information goes to the importance of being cautious in drawing conclusions about the various studies we see published in the media.  My reading from even respected medical journals needs to be done critically as the sample size, type of analysis and type of study may influence the apparent conclusions inappropriately.  My own view of the items I quoted above is only useful when looking at large populations of people for general recommendations and knowledge. They help the discussion but can't give the specifics of my own circumstances.My own feelings are that even if I knew that my exercise was going to lead to a worsening of my AF, I'd still do it.  The benefit for me, overall, far outweighs any statistical chance of problems.Todd