Rob Greaves (top left), Sean Greaves (top right) and Steve Boswell (bottom)

Rob Greaves, his brother Sean and their friend Steve Boswell are training for the fourth annual North Pole Marathon.

They will be swapping trainers for snow shoes for the April event.

"When I saw it I thought it was a really good challenge," said Mr Greaves, an Army PT instructor at St Athan, Vale of Glamorgan.

"I came across a website about the North Pole marathon when I was searching for a different sporting event," he said.

"I thought it would be a good way to raise money for charity too," he said.

As far as the climate goes... it'll just be a case of wrapping up warm Rob Greaves

After telling Sean and friend Steve, who are also in the Army, they signed up too and they are hoping to raise cash for The Royal Star and Garter - which provides nursing and therapeutic care to ex-service personnel - and the Stroke Association Cardiff.

"Like me, my brother is really into skiing and running too and we always said we should do an event together, so this is it," explained Mr Greaves, of Llantwit Major.

"And I believe this will be the first time two brothers will have competed in the race."

Although living in different parts of the UK, the trio have been undertaking gruelling training runs since signing up to prepare themselves for the challenge ahead.

NORTH POLE RACE FACTS The first marathon was run solo by Richard Donovan in 2002 in strong winds, with wind chill temperature dropping to -60C The following year, it became a race with 10 competitors Polar explorer Sir Ranulph Fiennes was among 15 runners in the 2004 marathon The 2006 race involved all 54 runners finishing and 500,000 euros being raised for charity England's Alison Hamlett set a new women's record in 2006 in 5:52:56.

"We've been doing conditioning training along the same lines as what you would do if you were training for a normal marathon," said Mr Greaves.

"But as far as the climate goes, well we can't train for that, it'll just be a case of wrapping up warm.

"We are probably going to have to wear snow shoes for the run, which are a bit like wearing a tennis racket under your shoes.

"I am still waiting for mine so I haven't had a chance to practice running with them on yet," he laughed.

The race course in the North Pole will be run entirely on ice but even so, Mr Greaves is hoping to finish the run in under five hours.

"I've read that some people can take up to 20 hours to complete the race because the wind can make it difficult," he said.

"But one person did it in three hours 45 minutes.

"If I can do it at around the four-hour mark I will be a happy man."