A runner died in the New York City Marathon. Have the risks changed as more people race?

She was just a few kilometres from the finish line.

A record-breaking 61,146 runners completed the New York City Marathon on Sunday. But Rachel Apa, despite being in what her father describes as perfect health, wasn't one of them.

The 24-year-old athlete collapsed near mile 24, or about 38.6 kilometres into the 42.2-kilometre race. Despite the life-saving efforts of bystanders, paramedics and then hospital doctors, she was pronounced dead later that night, her grieving parents told the New York Times.

"It's unfathomable," her father Steve Apa, who could not be reached by CBC News, told the news outlet.

Every year, more and more people vie for the chance to lace up their sneakers and push themselves 42.2 kilometres to cross that finish line. But every year, young and seemingly healthy people also die trying — typically of heart failure or cardiac arrest.

All told, including Rachel Apa, at least six runners have died racing in marathons and half-marathons around the world in the past six months alone. Still, experts say the incidence rate is very low, given that millions of people run them every year.

Marathons aren't any riskier than they were 20 years ago, but they are far more popular, explained Jack Goodman, a professor emeritus in kinesiology at the University of Toronto, and adjunct scientist of cardiovascular research at Toronto's University Health Network.

"When the population is so large, there are bound to be more cases, rare as they are," Goodman told CBC News.

Any time you have thousands of people in the same space, based on probabilities, one of them will have a cardiac event, Dr. Christopher Labos, a cardiologist and epidemiologist in Montreal, told CBC News.

"You just hear about it more in the news because