Reigning Ironman world champion Chris McCormack has accepted an invitation to compete in the Hy-Vee 5150 U.S. Championship Elite Cup triathlon on September 4 in Des Moines.

McCormack – or Macca, as the Australian is known in the triathlon world – will line up next to some of the world’s best 5150 triathletes to compete for a share of the largest prize purse in the history of the sport. More than $1.1 million will be up for grabs in the men’s and women’s professional races, with $151,500 going to the winners and an additional $51,500 in lap bonuses available in each race.

“HyVee Triathlon here we come. Registered and looking forward to racing. Need to build some bike power. Boys will be strong! Should be fun,” McCormack said in a Tweet to his fans on July 28.

Although he’s specialized in Ironman races in recent years, McCormack started his career in 1986 at the international distance (51.5 kilometers, or 5150), becoming the first and only athlete to be ranked Number 1 in the world and win the Triathlon World Championship and the ITU World Cup Series in the same year. After shifting his focus to the longer distance, he won Ironman Australia five years in a row (2002-2006) and triumphed at the Ford Ironman World Championship in Kona, Hawaii in 2007. Last year, he grabbed the lead 11.5 miles into the marathon in Kona and fended off a late challenge from Germany’s Andreas Raelert to capture his second Ironman world title.

McCormack recently returned to his 5150 roots, competing in ITU events in Kitsbühel, Austria and Hamburg, Germany this year and showing steady improvement as he eyes a possible bid for a spot on Australia’s 2012 Olympic team. His new book, I’m Here to Win: A World Champion’s Advice for Peak Performance was published in May.