MAKENA, Maui — Two-time defending women's champ Julie Dibens of England and defending men's champion Ruben Ruzafa of Spain are among the triathletes entered in tomorrow's 28.5-mile XTERRA World Championship.

The field of 550 triathletes, ranging in age from 12 to 72 and hailing from 36 states and 23 countries, will begin the race with a 1-mile swim in the Pacific Ocean. They'll follow that by mountain biking 20 miles on a course that climbs 3,000 feet up and down the lower slopes of Haleakala.

The third leg is a 7.5-mile trail run on lava rock, forest paths and beach sand.

The 34-year-old Dibens, who swam for LSU in the 1990s, led wire-to-wire last year. In 2007, she dominated the field, finishing more than eight minutes ahead of the runner-up.

This season, Dibens won XTERRA Guam and finished second at XTERRA Saipan and the Ironman UK.

Ruzafa was 24 last year when he became the youngest winner of the XTERRA World Cha mpionship. He came out of the water two minutes behind the leaders and pedaled into the lead by the 14th mile on the way to victory.

He placed second at XTERRA Italy on May 31.

The XTERRA World Championship is the last in a series of nearly 100 off-road triathlons held in 12 countries and 32 states.