Three days to run 135 miles in 50C Death Valley heat. And he's 75

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Few places are more deserving of their name than Death Valley at the height of summer. The Californian desert is blasted by the sun and temperatures that regularly climb to 50C in the shade.

Incredibly, it is into this furnace of sand and peril that a 75-year-old grandfather from Rochester will run next week as he lines up for one of the toughest tests of endurance on the planet.

Jack Denness will take just three days to run 135, stamina-sapping miles in the Badwater Ultramarathon, billed by its American organisers as the "world's toughest foot race". And Denness knows what he's letting himself in for, having completed the punishing route almost a dozen times.

"You have to be mad to do it," says the school caretaker from his home, where he lives with his wife, Mags. "It's one of the conditions of the race. You just can't explain to people what the heat is like. Imagine opening your oven door and facing that all day long. The road temperature gets up to 140 degrees [fahrenheit] sometimes."

Denness, who is running to raise money for Cerebal Palsy Care, already holds the record as the oldest man to complete the course, securing it as a sprightly 70-year-old back in 2005.

Having completed "ultras" in Mauritania, India, Niger and Morocco, he's qualified to call the Badwater event the "hardest one on the planet".

Each of the 90 competitors from all over the world mad enough to make the journey to Death Valley must arrive with a support team, which trails runners with energy drinks and cold water sprays.

Runners must complete the course within 60 hours to be in with a chance of bagging a medal, but the clock doesn't stop for nightfall. Denness will usually sleep for no more than five hours during the entire race, keeping his energy levels up with dried fruit, nuts, energy bars and sports drinks.

Before long, the mind starts to play tricks and hallucinations are common. Denness says he looks forward to them, as they "break the race up a bit".

He adds: "One time, I was totally knackered from heat exhaustion and I could hear this fellow behind me. I looked round and it was the Devil.

"He was all red, he had the horns and the tail and the trident. I looked at him, he looked at me, and we laughed at one another. Then he'd jump behind a rock or a tree. It kept going for about half an hour. It was great!"

The Devil rarely dogs Denness in the course of his everyday life, spent working at St William of Perth primary school. He retired ten years ago but quickly became bored.

Despite the rigours of the race, Denness says he takes care not to over-train. "I'm a firm believer that you should leave the mileage until the actual week," he says. "Save your energy for the race." So, every Sunday for the past nine weeks, Denness has run "only" a full marathon, fitting in two-mile jogs here and there during the week "when he's in the mood".

Some participants acclimatise by wearing five layers of clothing or jogging on the spot in a sauna in an attempt to simulate the heat of the desert. Denness doesn't bother. "Some people do those things but I think that weakens you. When I first started I used to do heat training, but I found I was exactly the same once I got out there. You've just got to go and do it."

Nor does he have a special diet, professing to "love a good fry-up" and primarily living on dinners of curries or fish and chips. "People say I must be eating pasta all the time but I don't like the stuff," he says. Instead, Denness puts his fitness down to his slim frame and taking cod liver oil since he was a boy. As for relaxing once the Badwater 135 is over, Denness says he'll crack open a few beers.

He won't be resting for too long, though: he has already booked for the 150-mile Sahara Race in Egypt in October.

To follow or support Denness, go to: www.facebook.com/deathvalleyjack