Starting on April 30, the Mirrim Wurnit Back Paddock Ultra, held near Romsey, was a race that had no specific distance - it ended when just one runner was left competing on the 6.706km course.

Backyard Ultra is a form of ultra marathon race where competitors must consecutively run the distance of 6.706km in less than an hour.

When each lap is completed the remaining time within the hour is used to recover before re-starting the loop the following hour, with the race ending with only one competitor left after all others have been eliminated.

McPhee won the Mirrim Wurnit Back Paddock Ultra - a mix of a trail and cross country course - after completing 31 laps of the circuit for a total distance of 207.886 kms.

Classified as one of five "silver ticket" events, 46-year-old McPhee's win has secured him one of 15 spots on the Australian squad for the Backyard Ultra World Team Championship to be held in October.

"Running 6.7kms in an hour is relatively easy for a good runner, but it's all about the attrition over time and obviously becomes harder the longer you go," McPhee said.

"It's a bit of a case of do you opt to run a bit faster and get more of a break inside the hour, or do you go a bit slower to be less fatigued, but also have less break time?

"I was getting about eight to 10 minute's break after leach lap where I'd be able to sit, have something to eat and then go back to the starting pen... if you don't make the lap within an hour or you're not in the starting pen when the next hour starts then you're eliminated."

McPhee started running at 11am on Saturday, April 30, and ran through until 6pm the following day.

"I went into the race expecting that I'd probably have to go about 48 hours to have to win it, so I got quite lucky to get away with 31 hours," McPhee said.

"After 31 hours I was getting sick of running at times, but I was still feeling physically comfortable had I had to keep going."

"With this sort of a race, as much as the 6.7kms doesn't feel too hard to get around in an hour, if you get anything wrong with your nutrition, hydration or shoes then you can very easily fall away because if you start to struggle you're in trouble.

"So I spend a lot of the time planning about what I need to do at the end of each hour to make sure I've got myself right for the next hour and I'm focused."

As well as winning the Mirrim Wurnit Back Paddock Ultra, a highlight for McPhee was the chance to meet revered endurance race designer and director Gary Cantrell, who traveled from America for the event.

McPhee on average runs about 100 to 120kms a week training for ultra marathon, the bulk of which is done at One Tree Hill.

Australia will be one of 43 "satellite events" competing at the World Team Championships in October.

Each team will have 15 runners, with the winning team to be the country whose 15 competitors combine for the most laps of their course.

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