CRAIG Robinson, Michael Sheridan and Simon Turnbull will test themselves to the absolute limit in August when they head overseas to take on Ultra Trail Mont Blanc.

The three mates will travel between France, Italy and Switzerland over two nights in a single, unsupported mountain race which includes running through passages at high altitude.

They'll see what their mental toughness is like when they start the race in the late afternoon before darkness descends and they have to keep pushing through the 166-kilometre trail.

It is expected to take between 30 and 40 hours to complete.

"I've done overnight trails before, but not two nights in a row so it's going to test me quite a lot mentally to stay alert, stay motivated and keep going because I've been out there in the early mornings before and it's just you and your head torch in the middle of nowhere," Robinson said.

"That's where you get to face your demons."

Robinson, Sheridan and Turnbull will occupy three of the 35 positions which Australians will occupy in amongst the total of more than 2000 competitors.

No other town or city in Australia has that many from a similar geographic location.

The trio gained selection in the race after amassing a total of nine points from similar races over an 18 month period. They were then successful in a ballot, but not before Robinson had already started training for Ironman.

It has proven to be the ideal lead-up.

"Out of the ballot last year there was 6000 entrants but only 2000 names drawn so if you miss the ballot you get a second entry the year after. But you have to re-qualify. Most of us have gotten in on our second entry," he said.

"You never know whether you're going to get in and I'd already booked to do Ironman and was pretty focussed on achieving a good time which I did achieve and it was just fortunate that in January I got the ticket to Mont Blanc.

"But I'd already come so far down the Ironman path that it was a bit hard to stop training for Ironman and start focusing solely on UTMB but the good thing is I've now got a good training base."

Robinson said he was looking forward to testing himself in conditions he enjoyed.

"I always loved running and being out in the bush is just something I enjoy doing and to have the opportunity to get over there is not something everyone gets," he said.

"That's one of the things about trail running that's so good; you get to test yourself and it's not until you're in those circumstances that you learn if you can keep pushing or not."