Allen at the 2008 Summer Olympics.
From an early age her parents encouraged her to run, and she used to frequently jog to primary school some 3 kilometres from home. At the age of four Allen began participating in Little Athletics at Landy Field in Geelong. She competed in junior athletics until the age of 14, winning a number of championships over 1500 m and 'cross-country' distance. Allen also enjoyed gymnastics in her early years, a sport that would prove important to her coordination skills during her triathlon career.
Allen graduated from Ballarat University as a nurse at age 20. She then travelled overseas. During one of her trips she met Marcel Diechtler in Kitzbühel, whom she married in 1999, who was a triathlon competitor for Austria. Diechtler encouraged Allen to take up triathlon, beginning in 1996.
After some years of successful racing around Europe Allen received Austrian citizenship in 2002 and started racing in the World Cup. She took silver in only her third World Cup in Hamburg, Germany and won silver at the European Championships in Valencia, Spain.
Just eight years after beginning the sport, Allen won the 2004 Olympic triathlon in Athens. At the end of the swim leg Allen was in 44th place in the field of 51. After the bicycle leg she was in 28th. During the run she progressively overtook twenty seven competitors to power past then-leader Australian Loretta Harrop just 150 metres from the finish line, winning the race in emphatic style.
Alongside her Olympic distance triathlon career, Allen showed several strong performances in racing at the Ironman distance. In 2002 she recorded the fastest Ironman debut time ever, completing the course in 8:58:24. She topped her performance in 2003, finishing in 8:54:01 hours, a personal record that still stands.
After the Olympic Games in Athens it was Allen's plan to only race at Ironman distances for 2005-2006, with the aim of winning the Ironman World Championships in Hawaii. After finishing 7th in 2002, Allen placed 5th in both 2005 and 2006.
In 2004, Kate Allen received the "Decoration of Honour in Gold for Services to the Republic of Austria" (Goldenes Ehrenzeichen für Verdienste um die Republik Österreich).
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