Explorer Ranulph Fiennes isn't one to shy away from a challenge. And that's putting it mildly.

Now aged 71, he's always looking for his next big adventure and plainly has no intention of ever slowing down. Over the last 48 years, Fiennes — a former SAS soldier who became the youngest captain in the British Army — has built up a CV that's full of extraordinary, world record-breaking achievements. He's made 22 major expeditions to the extremities of the globe, is the first explorer (with Mike Stroud) to cross the Antarctic continent unsupported and the only man alive to have travelled around the Earth’s circumpolar surface (more people have walked on the moon).

Five years ago he became the oldest Briton to scale Everest; and then, last April, the oldest Briton to complete the Marathon des Sables in the Sahara, running 156 miles over six days in 50-degree heat, and raising £2.5 million for Marie Curie Cancer Care in the process (in total, Fiennes' expeditions have raised more than £18 million for British charities).

Endurance

Naturally, Fiennes' age makes these record-breaking attempts more difficult, but another year on the calendar doesn't put him off trying, despite the toll it can take on his body. "Some hot expeditions have been excruciating, and some cold ones have been pretty lethal,” he admits. Take his six-day Sahara run, for instance, which has been called 'the toughest endurance test known to man'. “In the heat,” he notes, “age is more than just a number. Those over 65 are much more prone to heat stress than the young.”

Extreme cold is just as merciless — but it's also been a fact of Fiennes' challenge-seeking life. In the Antarctic, for example, wind-chill temperatures can drop to as low as -90C, which makes the most severe British winter seem balmy in comparison. “Each foray I've made into the Arctic and Antarctic has confirmed that low temperatures without the wind are relatively bearable,” says Fiennes, “providing that your clothing is sufficient. In Antarctica in particular you have high altitude to deal with, which lends itself to being very windy. In the polar regions, even the smallest of holes in your warm clothing can have major implications on your core temperature and survival.” The biggest danger in the cold is complacency, so you need to be constantly alert to freezing temperatures, even if you have experienced them many times before. “The cold can affect you in strange ways, mentally and physically,” he points out.

Challenge

Fiennes insists he's always been 'incredibly lucky' with his health, although his medical record says otherwise. Down the years he's suffered two heart attacks — one while he was 8,500 metres up Everest — undergone major bypass surgery and been treated for prostate cancer. Plus, during a North Pole expedition in 2000, frostbite claimed part of his left hand; and, despite his Everest and Eiger challenges, he suffers from vertigo. Hasn't he he ever thought about relaxing into an easier life away from the sub-zero mountain tops or blistering heat? The thought clearly appalls him.

“Retirement holds no allure for me,” he says. “Golf and fishing are for when you’re half-dead.” Remaining active is, it seems redundant to say, a crucial component of his life. Put it like this: in 2003, three months after a massive heart attack, three-day coma and double bypass, Fiennes (with Mike Stroud) had achieved the first-ever 7x7x7: seven marathons in seven consecutive days on all seven continents. Two years later came the Everest climb (“If you decide to have a go, whatever your age, you will have a one-in-12 chance of not coming back”); and two years after that he climbed the North Face of the Eiger. Retirement would, he worries, merely make him depressed. “It’s a sort of background shadow, a sort of fear, the thought of not having a challenge,” he says.

We can't all push ourselves to the limits like Ranulph Fiennes, of course. Yet, overall, his advice for staying young and keeping fit is refreshingly simple: “‘Staying young’ is a question of doing your best to do all the well-known medical 'dos' — and avoiding the 'don’ts',” he says. And rising to a challenge plainly doesn't hurt, either.