On May 7, Debi Hazelden became the first person to complete an "Iron Century", swimming, cycling and running 100 half Ironman distances in 100 days.

The previous best, set by a man, was 30.

Hazelden endured a Groundhog Day well beyond anything Punxsutawney Phil could conjure.

The Sydney-based Kiwi began her quest on January 28 with a 1.9km swim at Prince Alfred Park pool before whisking the family campervan to Centennial Park for a 90km cycle around a 3.8km loop and finishing with a 21.1km run. That tallied to 113km per day or, to give the sport's more familiar terminology in miles, an Ironman 70.3.

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The 36-year-old completed that task for 94 days from summer to autumn before travelling to Port Macquarie to prepare over days 95-99 for a full Ironman race as a finale.

Tapering was not her forte.

Eight pairs of running shoes, five sets of goggles and three flat tyres later she had closure. Hazelden was the 18th female overall in 11 hours 16 minutes.

She raised A$39,763 for the Red Cross with the support of partner John Mergler and nine-month-old son Ryder. They are still hoping to break the A$50,000 threshold.

"We planned it about 18 months out but I managed to fall pregnant in that time, which made the training harder," Hazelden says with a chuckle. "It was about doing something crazy and showing people they can push their boundaries. [The feat] was way tougher than I imagined. There were some dark moments; I was by myself quite a bit. You ask yourself 'why am I doing this?' and self-doubt creeps in.

"You've got to push those thoughts aside. It's more to do with mental than physical strength."

Change became an elixir to the monotony of completing loops.

"The best part of the day was when people popped up to say 'hello' running the reverse way after you'd been feeling sorry for yourself."

Her journey included occupational hazards. She faced 42-degree sun-cream smeared days in February, followed by rain on 16 of the first 18 days of March which saw water lap around her bike axles.

She considers herself fortunate to suffer just one injury.

"The laces were too tight on a new pair of running shoes which rubbed over the top of my foot. It was a case of getting the inflammation down. I endured a painful eight days, and thought I'd have to stop at 60 [days]. After a couple of acupuncture sessions it got better ... so I had to keep going."

That setback was tempered by basing her daily milestones on heart rate and time rather than speed and distance.

"I worried about that going into the race at the end, because I'm competitive. My heart rate averaged about 125 [beats per minute] on the run every day, and 110 on the bike.

"I knew if it was like that, I wouldn't be fatigued. If I worked the muscles too hard in the day, it would take too long to recover.

"The lack of physical toll it's taken is a complete surprise. I need downtime, but there is no obvious wear and tear. You don't have to do what I've done, but everyone is capable of a lot more than they think. It doesn't need to be endurance."

However, that's where it tends to lead for Hazelden, despite completing 11,412.9km in 100 days. Her next assignment is to qualify and return to Kona in Hawaii for October's Ironman world championships.