JAMA tally puts race-day cardiac death near one in 500,000 US distance-race finishes

Every unit in the JAMA denominator is a finish ^[2]. Discover's write-up states the arrest rate per participant ^[3]. A finish, though, is one runner completing one race, so someone who enters six half marathons a year is counted six times. One in 500,000 is a per-race figure, and a runner's own exposure grows with each race entered ^[3].

Spread over the 14 seasons from 2010 through 2023, the totals come to roughly 2.1 million finishes, 13 cardiac arrests and four cardiac deaths a year across all US marathons and half marathons combined ^[15][17]. Deaths were about a third of the arrest count, 59 against 176 ^[16]. Most of the runners whose hearts stopped in this data set survived ^[16].

The American Heart Association describes sudden cardiac arrest as the heart no longer pumping effectively, often because of a dangerous electrical rhythm ^[4]. Strenuous exercise, it says, can trigger one in a person with an underlying heart condition, including one that was never diagnosed ^[4]. On that account the race sets off a problem the runner already had ^[4]. Inherited disorders of the heart muscle or its electrical system fall in the same group, and they can leave athletes who look healthy vulnerable ^[6].

Early on, a cardiac arrest can look like the other causes of a runner going down. Discover calls prompt medical assessment essential for that reason ^[8].

Discover does not report a cause of death for either runner who died on Oct. 4 ^[1]. It cites a New York Post report on the Milwaukee runner, headlined as a Wisconsin father of four who collapsed near the finish line in his first half marathon ^[13]. For Cardiff it cites a Sunday Guardian report that organisers confirmed a runner had died after the race ^[14]. Two deaths on one day cannot show whether the underlying rate has moved. The 14-year US average of about four race-day cardiac deaths a year is the comparison the evidence supports ^[15].