@skins64 It's something I'm currently doing. I am an avid cyclist and have done many 100 mile rides all in around 5 hours. Probably what gave me arrythmia. Now I'm riding 45 minutes at about 80%. fortunately my left atria is not enlarged. Marathoners and long distance cyclists as well as cross country skiers have high incidence of arrythmias as do basketball players. I understand Larry Byrd struggles with AF. My local EP is also a cyclist. We've both scaled it back. Too much exercise isn't the best for your heart over time. I'm coming up on 75.

When you do endurance activity for many hours the adaptation is atria and left ventricular hypertrophy. This gives more chance for ectopic foci to develope. What is unique with cardiac muscle is that each muscle cell can develope it's own electrical current. So imagine having multiple distributors in your car firing out of synch with the main distributor.
There's the arrythmia. As the heart hypertrophies there are more chances for ectopic foci.

My goal now is to maintain good fitness but my 100 mile ride days are over.