“You have to forget your last marathon before you try another. Your mind can’t know what’s coming.”

I can’t think of anything that sums up the mindset of the long distance runner better than that – pushing yourself to the very brink of physical exhaustion, then when it’s all a fading memory, going off and doing it all again!

Translating it into a language more might understand, marathon running could well be the physical equivalent of the big night out – wake up on Saturday morning with a monster hangover, declare “never again”, but by the end of the following week, you’re ready to strap the beer goggles back on.

Humans….we’re a curious breed.

For Brisbane business heavyweight Brett Clark, marathon running has gone beyond an exercise in “memory purging” – it’s now entered the realm of “what’s next?” Even more accurately, “what’s left?”

Clark has already run the “Big Six” – New York, Boston, Chicago, London, Berlin and Tokyo, which is why he switching his attention from cities to continents.

Next week he flies (rather circuitously) to Antarctica to “compete” in the annual “ice marathon”, a gut busting 42.2km trek across the barren Union Glacier in the Southern Ellsworth Mountains, a mere 600 miles from the South Pole.

Forget any notion of crowds lining the course, cheering competitors on, or water refuelling stations with clowns juggling Gatorade bottles to the keep the spirits of runners high – the ice marathon will be run in minus 20 degree temperatures, with the added impost of 20 knot winds.

And as opposed to Boston or London which attract fields of 50,000 (many lucky winners of a balloted entry system) the ice marathon starting gun will fire within ear shot of just 59 runners, all of whom have paid a handsome sum for the privilege of physical and mental torture.

“There’s already an extraordinary kinship among the group, even though we’ve not yet met,“ Clark, the current Chairman of Queensland Rugby and board member of the Brisbane Olympic Games Organising Committee enthused. “We’ve been in contact via What’s App – I expect through the shared experience of the run, some will become lifelong friends.”

Businessman and extreme marathon runner Brett Clark/ (mage: Supplied)

There’s a good reason for the hefty entry fee – the logistics associated with getting the runners to the starting line are extraordinary, headlined by the deployment of special four-engined Russian ice jets that can cope with landing on the blue ice runway carved into Union Glacier.

There’s also accommodation, meals and on ground transport to attend to – pretty simple in Tokyo or New York, far less so on the highest, coldest, driest, windiest continent on earth, some 4,500km from the southern tip of Chile.

“All up there’s probably 48 hours of travel to get there,“ Clark said. “But that all adds to the adventure. There’s nothing that’s remotely normal about running a marathon on a glacier, starting with the fact I’ve been training in 30 degree temperatures – 50 degrees hotter than it will be down there!”

Having crossed the finish line in the world’s six major marathons, Clark’s revised goal is to become just the 394th person in the world to complete a 42km event in all seven continents. (Yes, there’s a website that keeps a record – take into account all the joggers in the world, it’s a genuinely exclusive club.)

Antarctica will be his fifth continent, leaving Africa and South America as the only “unticked boxes” in his global quest.

“Running is an excellent way to explore the world,” he says. “Getting to see these wonderful places, all while challenging yourself physically and mentally is something I find very rewarding. Most people run while listening to music. I never do. I like to lose myself in my thoughts, to hear my heart beat, and the sound of my lungs gasping for air! It keeps me in the moment, even if sometimes, you’re better off not being there!”

In keeping with his strong philanthropic bent, Clark’s Antarctica run also has a heavy charitable component. He and his wife Maria have been long time financial benefactors of the Mater’s Little Miracles program – the funds raised through the ice marathon (currently in excess of $185,000) will be channelled into “Catherine’s House”, a new perinatal and mental health facility the Mater Hospital established to assist mothers, babies and families.

“There are so many worthwhile charities in need of support,” he says. “Having experienced challenges with our own family, Maria and I take great pride in giving back.”

As for a targeted completion time, Clark is only prepared to predict he’s unlikely to surpass his personal best of 3 hours 13 minutes!

“I had my first hit out in my special ice running shoes the other day,” he said. “They went pretty well around Queensland Uni, but I’m predicting a pretty tough slog in temperatures of minus 20. On the positive side, I’m not going to run out of daylight!

“Through the group chat, I did learn that one of the four other Australian runners found out last week he has a fractured ankle, but rather than withdraw at the last minute, he’s planning to walk!

“Now that’s what you call a tough day at the office!”

Yes… humans, they’re an interesting breed.

• To donate to Brett Clark’s fundraising quest, go to Brett Clark Antarctic Marathon . The Clarks are going dollar for dollar with any monies raised.