With spring just weeks away and as people begin training for upcoming marathons, research shows men and women are naturally conditioned to run the endurance races differently. 

In a study published in the journal Medicine & Science in Sports & Exercise, scientists who researched runners in 14 marathons found that women who tackle the 26.2-mile (42-km) race paced themselves more evenly than men.

But whether this reflects a difference in nature, nurture or a combination of the two remains an open question.

"We need to find out why women are pacing differently," said Dr. Sandra Hunter, professor of exercise science at Marquette University in Milwaukee. "Is it the physiology, or is it a risk-taking psychology for the men?"

Hunter is one of several researchers who compared the sex differences in marathon pacing among 92,000 performances. While the extent varied, the sex difference in pacing occurred at all 14 marathons studied, the study showed.

Successful distance running requires appropriate and almost even pacing, so the findings suggest that women are superior to men in this way, Hunter said.

"The better runners tend not to slow dramatically," she said. "Among the slower runners, the sex difference widens."

One explanation is that men are naturally more competitive and risk-taking, going harder and slowing dramatically, Hunter said. But that theory ignores the physiological differences between the sexes.

"The best women will never outrun the best men," she said.

“Physiological differences explain that men will always be faster: Women have smaller hearts, more fat to carry, less hemoglobin, less muscle mass."

Exercise physiologist and running coach Tom Holland tells his marathoners it is not who goes fastest, it is who slows down the least.

Holland, author of “The Marathon Method,” preaches negative splits, or the strategy of running the second half of the race faster than the first.

“For the first eight to 10 miles (13-19 km) you have to run at an intensity that feels almost too easy, but for the average person, that takes a lot of discipline,” he said, adding he has seen many men hitting the wall at about mile 20 (32 km).

“As a racer I like to get behind women,” he said, “because historically they’re more even-paced.”

Hunter believes too much about exercise performance is based on men alone.

“The assumption is that women respond the same," she said. "Sometimes they do; sometimes they don’t.”