KAILUA-KONA, Hawaii » Australian Craig Alexander isn’t ready to give up his throne as he seeks his third straight Ironman World Championship title today.

"It’s never been a heavy crown to wear," he said. "I live for this race."

Alexander and Britain’s three-time defending champion Chrissie Wellington are among nearly 1,800 triathletes entered in one of the world’s toughest endurance races, which includes a 2.4-mile swim, 112-mile bike ride and 26.2-mile run in punishing conditions.

Each of the 121 professionals and more than 1,600 amateurs will test their mettle against the elements and each other.

"I know I’ve done everything I can to do the best I possibly can," said the 33-year-old Wellington, who set the women’s course record last year. "I am stronger, faster and fitter. I definitely feel I am capable of lowering the course record. But you never know what (volcano goddess) Madame Pele will throw at us."

The cannon blast will ring across Kailua Bay at 6:30 a.m., sending swimmers 1.2 miles into the swells of the Pacific Ocean and back again. On Kailua Pier, they jump on their bikes and speed north along Queen Kaahumanu Highway to Hawi, the tiny town that serves as the turnaround.

Australian Chris McCormack is looking to add to his 2007 world title, as is two-time champion American Tim DeBoom (2001-02). The field also includes a trio of former winners from Germany in Normann Stadler (2004, ’06), Faris Al-Sultan (2005) and Tomas Hellriegel (1997).

Among those looking to deny Wellington a fourth crown are Australian Mirinda Carfrae, 29, who set a women’s run record last year in what was her first ever marathon.

Other standouts include Spain’s Virginia Berasaegui, who was third last year, former six-time champion Natascha Badmann of Switzerland and 1995 champ American Karen Smyers.