It was when the organisers of the Jungle Marathon briefed the competitors on the dangers of the rainforest that Sophie Collett began to worry that she had bitten off more than she could chew.

“Six months beforehand, I’d run the Marathon des Sables,” she says. “That was 151 miles across the Sahara in Morocco, in temperatures which regularly topped 40C. So I thought I knew a thing or two about physical challenge.

“But then they got one of the guides, Gil Serique, to talk us through the nasties that lurked on the trail up ahead, and my blood ran cold.”

The Jungle Marathon is 125 miles, and is run over seven days through the Amazon rainforest in Brazil. Its founder, Shirley Thompson, set out to create “the toughest event in the world”, but, as Collett discovered, as she sat with 87 other competitors on a sandbank by the river, it was not just exhaustion she had to worry about.

“For a start, there are the spiders,” she says. “Then the scorpions, and the jaguars and the piranhas. But perhaps the worst part of the briefing was when we were told about the poisonous snakes.

“Apparently, there’s a kind of snake that sits coiled on the forest floor and can jump forward [10ft] to attack its prey. Serique told us that if we were bitten by such a snake, we’d have only eight hours to get to a hospital,” remembers Collett. “The thing was, it had taken me two days of continuous travelling to reach that part of the jungle. I had my doubts about making it out in time.”

It is at this point that most people would probably have packed their bags and decided that discretion was the better part of valour. But then most people don’t sign up for a race like this in the first place. The Jungle Marathon, which was filmed for a documentary to be shown on ITV4 on December 4, is just the latest addition to the booming sport known as ultramarathons (see below) that has swept across Britain and other countries over the past five years.

At a time when plain old marathons and even Ironman competitions have become run of the mill, an increasing number of super-fit competitors are looking for ever more demanding challenges. There are races across deserts, over ice and up mountains. But it is hard to argue that the craze has not reached its zenith with this race through a rainforest.

Competitors must stump up €2,400 (£1,975) plus their travel expenses. The race itself follows the watercourse of the Tapajos river, and is broken down into six stages: 10 miles, 15 miles, 19 miles, 12 miles, 54 miles and 15 miles in length. Once it was under way, it became clear that the biggest hazard Collett faced wasn’t the animals. It was the plants.

“I hadn’t appreciated how ‘in the jungle’ the race was going to be,” says Collett, who works as a physiotherapist in a London hospital. “I thought most of it would be on tracks. But at times we were just blundering through the forest, following little ribbons the race organisers had put on the trees to show the route.”

Her progress was made even more difficult by the fact that, like the other competitors, she had to carry her own food and camping equipment. This included large quantities of energy drinks, rehydration electrolytes, freeze-dried food such as beef stroganoff and apple pie and custard, plus a change of running clothes - all packed into a 30-litre ruck-sack. “I just barged through it all, and by the end of the race my legs, arms and stomach were completely shredded.”

While the physical punishment was intense, Collett found the arduous route helped her mental state. “It actually helped to pass the time,” she says. “Because you have to concentrate so hard on what you’re doing. It was also nice to feel your whole body working, whether you were climbing over fallen tree trunks or wading through a swamp. I’d be looking at my watch and constantly being surprised at how much time had passed.” In that respect, it was much easier than the Marathon des Sables. “There, I had to run across a salt flat for 20 miles,” she says. “In places like that it’s hard to find the motivation to keep running.”

That’s not to say the Jungle Marathon was easy. With the temperature regularly topping 30C, and humidity above 90%, Collett and her fellow competitors faced the danger of heat exhaustion. Under such conditions the body is no longer able to keep itself cool, and the core temperature continues to rise until the brain starts to cook. At this point, the victim will lose consciousness and can slip into a coma.

A first aid hut was established at the end of each stage, helping runners with IV drips for exhaustion. With her medical experience, Collett volunteered to assist when she could. Of the 88 runners who started, 63 finished. Two were evacuated for hospital treatment.

For most of the field, the penultimate stage was the worst - 54 miles of tortuous hills, jungle, two water crossings, and a hot, sandy finish. If anything, Collett suffered more than most, as she had caught a powerful gastric bug.

“I think I got it from swallowing water when I was wading through a swamp,” she says. “About three hours into the longest day I started to feel really queasy, and at one of the medical points a doctor told me I looked awful. I tried to eat and drink, but I couldn’t get it down, and as soon as I left the checkpoint it hit me. I was just running along being sick.”

It’s a measure of Collett’s determination that she kept going for several more hours before she was forced by the organisers to stop. Eventually, they let her carry on. “The last three or four miles were the worst,” she says. “It was dark, there was no one around, and I was running through soft sand. It felt like it was never, ever going to end.” It took her 23 hours to complete the stage.

Not surprisingly, the end of the race brought a powerful sense of achievement. “We were just over the moon,” she remembers. “But also a little sad that it was over. Looking back, I realise I actually loved being in such a remote place, and I loved the camaraderie generated by such an extreme environment. At times like that, you make good friends really quickly.” It’s also likely that she has cured her long-standing fear of spiders. “When I went there, I had a massive phobia, but of course spiders are all over the place in the jungle. On one day there was a huge tarantula in our camp that was larger than my hand. And on one of the stages, at night, I found myself crawling under a log that clearly harboured an awful lot of insects. But there was no question of getting freaked out - I was concentrating so hard on the race, I just got on with it.”

A jog around the park will never seem the same again.

TOUGHER THAN THE REST
An ultramarathon is any race longer than the Olympic distance of 26 miles, 385 yards. There are hundreds each year - these are the toughest.

Marathon des Sables www.darbaroud.com A six-day, 151-mile run through the Sahara in temperatures that regularly top 40C. This year’s event - the 23rd - was the longest and largest, with a field of 801 competitors, including more than 250 Britons.

Gobi March www.4deserts.com Run 155 miles across the Gobi desert in China in six days. The race is one of a series of four desert ultramarathons held each year. The others are the Atacama Crossing in Chile, the Sahara Race and the Last Desert (Antarctica).

Badwater Ultramarathon www.badwater.com This is 135 miles nonstop, starting in Death Valley, California (280ft below sea level), and ending at an elevation of 8,360ft on Mount Whitney. The invitation-only field must endure temperatures of up to 55C and climb a total of 13,000ft.

The 3100 Mile Race www.3100.ws The world’s longest foot race - and it’s around one block in Queens, New York. Competitors have 51 days to complete 5,649 laps of the 0.5488mile course, averaging over 60 miles a day.

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