Temperatures approaching 90 degrees forced an early end to the 30th annual Chicago Marathon.
The New York City marathon this Sunday comes on the heels of a dramatic Chicago Marathon, in which two people died and the course was shut down because of record heat.
The number of people running marathons has quadrupled since the year 2000, and, if statistics bear out, an average of eight people will die from cardiac arrest while running a marathon in the United States this year.
So why are all these people signing up, and who should be running them to begin with? Malissa Wood, a cardiac specialist and marathon runner, talks about the marathon phenomenon and the toll it takes on a runner's body.
On our blog, an open thread: Are too many people attempting the marathon?