How Much Running is Too Much Running

I ran a Halloween race today. This guy captures the
spirit of the event. Source

I ran a 5K today, and after the race I met an old guy who ran 80 races this year so far, and plans to do two more this week. There was a woman there who does more than he does.

I have always thought of running as healthy, in part because I feel it should help me lose weight, but sadly the data does not always support that. One has to exercise a lot to receive weight loss from exercising -- 6-7 hours a week.

I keep looking for data that shows a graph of miles run against life expectancy, and I am certain nothing like that exists. It seems that very long races can weaken the heart, and the heart adapts by changing shape: enlarging here, thickening there.  On the other hand, running clearly helps; it is just that too much running stops helping -- and there may be a best point.

Too much exercise can be damaging to the heart as well as the joints, and it can lead to atrial fibrillation, something that I am worried about. Atrial fibrillation is five times higher in endurance athletes.

Thus site discusses the changes in endurance athlete's hearts after an event -- for example a professional cycling race. The athlete's right ventricle function decreased, but it self-corrected after a week. This may reinforce the benefit of rest to prevent permanent scarring.