Running an event based on pushing forward doesn’t allow much time for looking back.

Over the past quarter century, Dr. Jim Barahal has overseen the Honolulu Marathon’s growth into one of the world’s largest races, and more than 20,000 are expected to congregate along Ala Moana Boulevard on Sunday morning for the start of the 39th annual event.

But even as he prepares for his 25th year as race president, Barahal is more concerned with the task ahead than the milestone he’ll pass on Sunday.

"We used to have a saying in running — you’re only as good as your last workout," Barahal said. "I suppose someday I’ll look back and realize I did this for a very long time and hopefully feel good about what we accomplished, but that’s not what we’re doing right now. We’re really focusing on Sunday, and on Monday we’ll start focusing on next year. I think that’s the mind-set you have to have."

The marathon hits the streets at 5 a.m. Sunday. The course runs through downtown Honolulu, into Waikiki and on toward Hawaii Kai, where the route turns back toward the finish at Kapiolani Park.

As of Monday, a little less than 21,000 had entered the race, with more expected to sign up at this week’s marathon expo at the Hawaii Convention Center. Last year, 22,806 entered and 20,268 finished the race.

"I think we’re on track," Barahal said. "We’re up in Hawaii, we’re up on the mainland, we’re up in Europe and we’re a little down in Japan. So overall we’re running the same or just a little ahead."

Last-minute entrants willing to pay the $260 fee can still register Wednesday through Saturday.

"Astonishingly enough, we always get about a thousand entries race week," Barahal said.

Barahal said it’s difficult to say whether the natural disasters in Japan in March had an effect on the entries from Japan, but "I suspect, looking back, it probably did."

The mass of runners will be led by a group of elite competitors headlined by both of last year’s champions. Nicholas Chelimo of Kenya returns to defend the men’s crown and will contend with a field that includes 2008 and ’09 champion Patrick Ivuti.

Belainesh Gebre of Ethiopia held off three-time champion Svetlana Zakharova of Russia to win last year’s women’s title. Both are back, with Zakharova making her 10th appearance in the event.