The Carlsbad 5000 is billed as the world’s fastest 5K and rightfully so. Sixteen world records and eight U.S. records have been set on the course that overlooks Pacific Ocean waves breaking on the beach. But if you’re Tracy Sundlun, the event’s executive race director, you’re always tinkering, always looking for ways to improve.

For Sunday’s 31st edition of the race affectionately known as the ’Bad 5K, Sundlun has tinkered some more. For the second year in a row the course has been significantly altered for the professionals.

A year ago, Sundlun introduced two loops along Carlsbad Boulevard, giving the thousands of spectators more opportunity to cheer the elites. This year, the start is being moved from Carlsbad Village Drive to Carlsbad Boulevard. Plus, mimicking track and field, the professionals will run the two loops on Carlsbad Boulevard counter-clockwise.

“Even for those athletes as beautifully efficient as Bernard Lagat, they backed off before every turn,” said Sundlun. “They went into them running clockwise, which is not what they’re used to doing on the track. They’ve spent all their lives running counter-clockwise.”

The new layout is only for the pro runners and wheelchair athletes. Age-groupers will still run the course that essentially has stayed the same since the race’s 1986 inception.

The changes were incorporated for two reasons—to enhance the spectator experience and create a course and environment that’s more beneficial for the elite runners.

The start will be just south of the Carlsbad Boulevard and Carlsbad Village Drive intersection, amid the heart of the spectators.

For last year’s 30th anniversary the start of the professional races was moved to where the race finishes on Carlsbad Village Drive. After consulting with runners and coaches, it was determined that the runners didn’t have enough of a build-up before the turn on Carlsbad Boulevard, where the runners were quickly met with a slight elevation gain.

“It didn’t help the athletes,” said Sundlun.

Paul Greer, head coach of the San Diego Track Club, likes the changes.

“What moves athletes to break records or run great times is tremendous spectator participation,” Greer said. “The advantage Tracy gave the athletes this year is putting them in the midst of the crowd. I think it’s going to have a stadium feel to it. The runners, they’ll actually feel the crowd as well as hear them.”

As usual, elite athlete recruiter Matt Turnbull has pulled together a deep set of pro runners. Defending champion Lawi Lalang of Kenya returns to defend his title. The ageless Lagat, 41, is back after setting the masters 5K road record last at Carlsbad, finishing in 13:40. A young runner to keep an eye on is 19-year-old Debeli Gezmu. Meseret Defar’s cousin, Gezmu has been clocked in the 5,000 on the track in 13:29.81.

On the women’s side, Defar is back. The two-time Olympic 5,000-meter champion set the women’s course record at Carlsbad 10 years ago, running 14:46. Defar is expected to be pushed by 21-year-old Kenyan Caroline Kipkirui, who owns a 5,000-meter track best of 15:24.66.

Sunday’s racing begins at 7 a.m. with the masters events.

On Saturday, the Junior Carlsbad 5000 1-mile races begin at 7:20 a.m. Added to this year’s schedule is an adult one-mile race offering $3,000 in prize money.