"This kind of slowing probably means the runner was shuffling or walking the last several miles," he said. Only 5 percent of women experienced the same slowing.
Aside from gender, the biggest pace predictor was overall finishing time. "For example, among those finishing in about three hours, the typical amount of slowing was 6.9 percent for men and 5.5 percent for women." For those finishing in about 5 hours, those numbers are 18.8 percent and 14.4 percent, respectively.
A separate study published in the Journal of Strength & Conditioning Research found much the same: In studying times of nonelite runners who finished in under 5 hours in the 2007 and 2009 Chicago Marathons, where runner times were recorded every five kilometers, women slowed less than men, especially between the 30 kilometer and 40 kilometer marks (a marathon is 42.2 kilometers).
The Medicine & Science in Sports & Exercise paper points to a few factors that could make for the difference in gender pacing. Men are more susceptible to muscle glycogen depletion and hyperthermia than women. Women have lower respiratory exchange ratio, which means that we burn more fat and fewer carbohydrates. Women also have more of the types of muscle fibers that are fatigue- resistant than men do.
But Deaner thinks that pacing differences aren't physiological.
"I suspect the biggest reason is that, in most situations, men are more likely to be overconfident and willing to take risks," he said. "In the marathon, that means that men are more likely to start off at a very ambitious pace. An ambitious pace will pay off sometimes with a great performance, but it also makes it more likely that a runner will crash."
Deaner, who has run three marathons, says that the study focused on the nonelite runners for their research because the pros and semipros pace themselves well, and the rest of us have not been studied much at all.