It can be long, tiring and painful, but studies show many more females are starting to take on a previously male-dominated activity: running.

The number of female runners and joggers has increased by 14.2 percent during a five-year time period from 2000 to 2005, said Larry Weindruch, spokesman for the National Sporting Goods Association (NSGA).

"One of the things we look at in a sport or activity is if it's a mature sport or a new sport. Running is a mature sport," Weindruch said. A mature sport always stays in the same range, he said. It can grow if the population is growing, it may go up one year or down the next, and sometimes there is no explanation for the growth, he said.

In 2000, there were 22.8 million total participants, of which 11.3 million were females. In 2005, there were 29.2 million total participants, of which 12.9 million were females, Weindruch said.

"A participant is defined as a person age seven or older who takes part in the sport or activity more than once in a calendar year," Weindruch said.

The numbers come from published surveys conducted by the NSGA, he said.

Many popular shoe companies seem to be aware of the growth in women's running. In 2001, Nike created separate footwear department and designed running shoes exclusively for women. This year, the company teamed up with Apple to make a running shoe with a small sensor in it for music and data collection, among other features, according to Nike's Web site.

"I think overall we've seen an increase in fitness activity for women, and running is a popular way to do that," said Chip Harrison, head strength and conditioning coach at Penn State. He said he thinks many people enjoy running because they can do it outdoors and not be tied down to a time and location; they like the flexibility of the activity.

"We put together a beginner's running group, and it's probably 60 to 80 percent women," said Martin Mazur, Nittany Valley Running Club's webmaster and newsletter editor. He said the group puts together many group runs, and in the past, it was all guys, but he noticed now that there are many more women involved.

"More women are getting into running and being athletic," he said. He said he has not only noticed an increase in college-aged students running, but also middle-aged women as well.

"It's healthier, a great way to lose weight and can be a social thing too," he added.

For women who want to get into running, it is best to start out slowly, Harrison said.