According to the Journal of the American College of Cardiology, the risk of dying from a cardiac arrest is about 1 in 50,000 for endurance athletes who exercise for three hours or more.
“I went to a fight the other night, and a hockey game broke out.”
– Rodney Dangerfield
That is, if you run marathons or participate in other forms of exercise which last for three hours or more, that distressing number is the approximate risk of suffering an acute heart attack or sudden cardiac death during – or within 24 hours of – the strenuous effort.
The sad truth is that for every 50,000 athletes, one will be stricken during such prolonged activity. Therefore, running a marathon or cycling intensely for three hours is riskier than taking a commercial airline flight.
In fact, any athlete who participates in a strenuous test of endurance lasting about three hours or more has an increased chance of dying during – and for 24 hours following – the exertion, even when the athlete’s chance of a sudden death is compared with the risk incurred by a cigarette-smoking, couch potato who spends the same 24 hours drinking beer and watching television. This is what is known as a U bend phenomenon, in which one extreme is equal to the opposite.
“Hobbes: Jump! Jump! Jump! I win!
Calvin: You win? Aaugghh! You won last time! I hate it when you win! Aarrggh! Mff! Gnnk! I hate this game! I hate the whole world! Aghhh! What a stupid game! You must have cheated! You must have used some sneaky, underhanded mindmeld to make me lose! I hate you! I didn’t want to play this idiotic game in the first place! I knew you’d cheat! I knew you’d win! Oh! Oh! Aarg! [Calvin runs in circles around Hobbes screaming “Aaaaaaaaaaaa”, then falls over.]
Hobbes: Look, it’s just a game.
Calvin: I know! You should see me when I lose in real life!”
– Bill Watterson
Knowledge Guild 