Exercise level ,cardiovascular risk reduction and risk of atrial fibrillation

 Six years ago  after I had recovered from my pacemaker implantation and the subsequent complications  (pulmonary emboli and pocket hematoma)  I mentioned to my EP cardiologist that I believed that I could run a half marathon. I had abandoned thoughts of completing a full marathon  because for  the proceeding two years I had barely finished in under six hour which was the cut off time to be officially counted as a finisher. for the full marathon.

The EP doc said that is not a good idea and when asked why he mentioned the risk of atrial fibrillation. I thought he was wrong but let the mater drop. I did not doubt that there is a relationship between running and AF but felt sure that the level of exercise sufficient to train for a half marathon was not in the range where there would be worry about AF.

The irony of recently seeing the EP doc's picture posted by him on a social medium site showing him with the half marathon medal along with his finishing time  did not go unnoticed. 

This is a good time to review the current recommendation for exercise to reduce cardiovascular risk,at what level of exercise  does it becomes too much or a good thing,and at what level does there appear to be an increased risk of atrial fibrillation. 

Currently the widely accepted view  and the WHO recommendation is that as a minimum one should exercise at a  level of 8 met hours per week.This is equivalent to 1/2 hr of moderate exercise for five days a week. Moderate is defined at a 3-6 Met level.8 met hours per week can also be achieved by vigorous exercise ( defined at greater then 7 mets) for 1.25 hours per day for five days  per week.

8 met hours per week is good but it is widely believed that at least a bit more is better, for example exercise at twice the minimum level would be better in term of cardiovascular risk reduction.This would be exercising at a moderate intensity for one hour a day for five days a week. 

So it seems in terms of cardiovascular risk reduction more is better but there must be limits to that.Is there a level of exercise beyond which there is no further improvement in risk reduction?

Eisvogel's data analysis suggest that that level is around 41 met hours per week. That is five times the minimum or 2.5 hours of moderate exercise per day five times a week . Interestingly the risk reduction exercise volume curve flattens out at a much lower level for vigorous  exercise, at 11 Met hrs per week according to Eisjvogels analysis data from Wen and from Aren.    

At what level of exercise can we expect an increased risk of atrial fibrillation?

Data from Ricci 2018 suggests that level may be about 55 met hours per week or 7 times the minimum recommended dose which would be 3.5 hr moderate exercise per day five times a week 

The level of exercise sufficient to train for a half marathon is definitely less than the estimated threshold for increased risk of atrial fibrillation. Check out any of the numerous half marathon training program and you will see the volume suggested is much less than 7 times the minimal WHO recommended exercise level.