McDonald, 30, won his first Ironman triathlon — contested over a torturous 4km swim, 196km cycle and 42km marathon run — at Louisville last year.

He returned to defend his Louisville crown last month but fell just short, finishing a very brave second.

McDonald, and any other triathlete for that matter, would normally give himself at least a fortnight to recover from arguably the most arduous sport in the world.

But the Albury athlete, spurred on by a dare from a female competitor, did the virtually unheard-of and immediately began preparing to do it all again in Wisconsin seven days later.

“I spent the six days between (races) just getting the blood flowing in my legs and generally just chilin’ (sic),” McDonald wrote in his blog.

“A lot of people were asking me ‘Why?’ and I (would) say ‘why not?’.”

By his own admission, McDonald thought he was merely making up the numbers — but not for long.

He enjoyed his best swim of the season to emerge from Lake Monona with a short lead.

“I hit the shore of the lake with a huge grin on my face ... I now had the opportunity to make several decisions on how I would go about the day,” he wrote.

What he decided was to lead for the rest of race, winning the triathlon in a course record time.

“The person I have to thank the most is my number one supporter and loving wife Marilyn, this whole two weeks was a huge team effort,” he said.

McDonald and his wife live in the US for six months a year and come home to Albury for the off-season.

He become a professional Ironman in 2004.

Before going into full-time training McDonald tipped the scales at 113kg, 27kg heavier than his ideal race weight.