Re: Aerobic Exercise

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Posted by Steve Giddings on October 24, 2002 at 07:33:18:

In Reply to: Aerobic Exercise posted by Bruce Bauer on October 23, 2002 at 14:42:51:

I've made a number of posts on this subject in the past. You can find them using the search feature on the web site.

By background, I have an academic background in and current research interest in exercise physiology, motiviation for exercise and its impact on chronic diseases, particularly diabetes. I've been a"compulsive" exerciser and for the last 10 years, a competitive masters athlete. (So sue me, I'm biased!)

It is very difficult to sort out the effect of chronic exercise in the pathogenesis of A fib. There are a number of misconceptions, however, the basic one being that aerobic training "damages" or "stretches" the heart muscle. That is simply not true. The heart responds to exercise by hypertrophying, growing bigger to accept the increased demands place on it. One might even argue the reverse, that the heart involutes when it is not used as it was originally designed to function. There is no evidence for scarring. In fact, there is the reverse, the heart muscle that is trained has a better blood supply and is better equipped biochemically to extract fuel and oxygen from the blood and convert it into contractile energy than the heart from sedentary individuals.

Are aerobic exercisers more likely to get atrial fibrillation? This is hard to say. They are certainly more likely to notice it and to do something about it because it limits their peorformance. It is quite likely that the same drive that led to many who post to this site to exercise, also drove them to do something definitive about their a fib when it occured. What I am saying here is that we are a preselected group.

Bigger hearts, however, are probably more likely to develop af if something else happens to damage them and set up the substrate for the electrical imbalance between adjacent areas of the heart that allow a fib to occur. Once the pattern has been set (an episode has occured) biochemical changes occur in the heart that make it more likely to happen again.

What I would argue strongly is that exercise is good. People who exercise regularly have less hypertension, less vascular disease, less diabetes, fewer strokes. They live longer and live better. Neither Paul Teague nor Kenneth Cooper have published anything anywhere in peer reviewed literature (ie that has a credible scientific basis) to support the contention that exercise per se causes a fib. There are 2 papers that report an apparent increased frquency in exercisers, one in the Lancet, the other I can't recall, but the findings in both can be explained by selection bias.
To prove exsercise causes af in humans would be quite difficult. You would need to do a prospective study in which individuals are randomized to exercise or no exercise and followed to a predetermined point that proves the null hypothesis (exercise does not cause af with a certain degree of certainty, damn those statisticians) or the difference in number of events diverges between groups significantly.

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