Starting August 31, Mr Brockman will clock off his work as an apprentice electrician each day and pound the pavement for 42km to raise funds for the Australian Red Cross.

Running is something the Forbes boy has only picked up since his relocation to Sydney to take up his trade - but he's fast developing a passion for it.

"I reckon it might be my life after this, I love it. I just absolutely love it," he said.

And now he's decided to run to raise funds for the Australian Red Cross to help them help people in need.

"Every Tuesday when I venture into the city for TAFE I always see homeless people doing it tough and sleeping rough," he said.

"I feel like I'm really in a position where I should be able to help.".

Day to day, Mr Brockmann will reach for something immediate such as food, or his hoodie, but he's hoping his marathon effort will draw support to provide shelter to the homeless and support to families living in poverty as well.

"I'm a bit of a nut," he admits, "but I want to see how far I can challenge myself."

The 21-year-old knows the mental challenge could well be the biggest part of it.

Earlier this month he challenged himself to a 100km run, from Randwick to Palm Beach and back, and 58km into that he was really starting to question his reasoning.

"If your why is bigger than your reason to quit, then you won't quit," he said.

And this fundraising challenge is a pretty big "why" for Mr Brockmann.

"I know what I'm up against," he said. "I've been training a lot to get a base to work off."

He has several 42km tracks he'll rotate, ranging from doing 12 laps of Centennial Park to powering out 42km on the treadmill.

Mr Brockmann added he'd already run 14 half marathons in 14 days, but was planning to continue his heavy training for another week and then back off until his official start date.

To support Nedd, go online to https://fundraise.redcross.org.au/fundraisers/neddbrockmann