No longer a man's race

Researchers analyzed data from more than 400,000 runners who participated in 10 of the largest 10km (6.2 mile) races in the U.S. from as early as 2002 through 2011.

Other findings from the study, the first to analyze performance trends among the nation's 10km runners, include:

• The top groups of men and women appear to be getting faster
• The fastest men are also increasingly younger
• There are more sub-hour finishers, with increasingly more women accomplishing this feat compared to men
• An increasing percentage of finishers, however, are completing races in more than one hour

The study was published online in the Journal of Strength and Conditioning Research.

"It seems that as these large races have more people participating, we have slower runners, but I see that as a positive thing," said Dan Cushman, M.D., lead author of the study.

"It's not just elite runners or former high school athletes running today's 10km races, there are more everyday people running this distance," Cushman said. "One of the best things we can do to improve our health is exercise and taking on a 10km race is a great goal."

Cushman is a clinical instructor in physical medicine and rehabilitation at Northwestern University Feinberg School of Medicine and chief resident at the Rehabilitation Institute of Chicago.

Ten-kilometer races have become increasingly popular in the U.S. over the past decade with 1.3 million people participating in such races in 2010. Women began outnumbering men in the 2006 and 2007 timeframe and today make up the majority of runners who participate in these 10 large 10km races in the U.S., Cushman said.

"Coaches and trainers can use this information to develop more women-specific 10km training programs to accommodate this surge of female middle-distance runners," Cushman said.