Year after year, tens of thousands lace up to take part in the Ottawa Race Weekend. Some are first-timers, but many, like Eric Gillis, come back time and time again to take part in the course.

"It's just an amazing event," Gillis says. "I really enjoy being here. It's top-notch. I've been to a few marathons in North America, and this is just right up there."

The sold-out event has 38,799 runners registered this year. It's a fast course with few hills -- a Boston Marathon qualifier. And, say the runners, the crowd support is outstanding.

"Most of the people know me and applaud for me," says Lioudmila Kortchaguila. "They cry 'Mila, go, go!' It's just nice."

Adds Rick Ball, "Honestly, when you're just about ready to give up and you have nothing left in the tank, it's that crowd support that gets you across the finish line. Ottawa is the best in the country for crowd support, I find."

As the marathon grows, Run Ottawa -- the organizer -- takes a wait-and-see approach about how many participants it can accommodate. This year, it's taking a new approach with the half marathon: a wave-start time.

"The wave start is designed to put the runners out on the course, with a bit more space," says John Halverson of Run Ottawa. "Hopefully that will alleviate some of the congestion and hopefully at the finish line as well."

Other factors to consider for long-term growth: volunteer availability, road closures and congestion.

"I think we'll manage some small growth every year, but we're not going to go gangbusters," says Halverson.

With a report from CTV Ottawa's Karen Soloman