The hot, dry African air scorches my lungs as I start to run uphill; the sand underfoot makes it hard for my feet to keep their grip. I have to ask myself what on earth I am doing here, competing in one of the world's toughest races.
In my teens, I suffered from chronic fatigue syndrome and was largely bedridden for seven years. I have always looked at runners with awe; I never thought I'd join their ranks. Particularly not in an event such as the Lewa Marathon, which takes place in a wildlife conservation area in north-east Kenya, complete with armed guards and spotter aircraft circling to keep the lions at bay. It is a runner's nightmare: a combination of sharp inclines and shingle descents, made even more punishing by thin air and fierce heat. Yet for better or worse, this is where I chose to start my running career.
We meet at the start line at six, under a cold, pink dawn. As I wait, I meet Kenyan marathon legend and former world record holder Paul Tergat. "I always come to Lewa," he tells me. "It is a great marathon, through a marvellous landscape. More than that, it brings people together from across the country. Running is very important to Kenya."
The atmosphere at the start is electric. The Europeans and Americans, decked with iPods and dry-fast Lycra, squat and lunge to stretch their muscles. Of those that have flown long-haul to be here, most arrived early to spend a week acclimatising with gentle jogs and non-alcoholic sundowners. The locals seem more relaxed, loafing around the edge chatting, a few in sandals improvised from tyres. Many of them walk or jog to the race on the day. To raise his bus fare into Lewa, the winner, Benson Kaptikou, had to sell his goat.
There is a short delay while we wait for word that the course is free from game. The gun suddenly goes off and the 750 runners crash over the line. The track goes into a gentle rise, and we soon spread into an ant-like column, bright against the tawny grass.
The first few kilometres are relatively easy. The race director, record-breaking 1960s athlete Bruce Tulloh, has warned me against starting too fast. "The easiest mistake to make is to tire yourself out too soon," he said. "Enjoy the first part; you'll need all your energy when you reach the hills at the 5km mark."
Tulloh was right. There are two long ascents, and they are heart-burstingly tough. Above the soft pat of feet hitting the track, I can hear the breath of the runners around me as they strain to get oxygen into their lungs. A couple of months training in Hyde Park was scant preparation. By the time I crest the second ridge I am panting like a dog. I have never been more eager for glucose: there are water stations every 2.5km, with music, dancers and spectators handing out sponges, and at each I slug back water and Lucozade.
As we run, the sun becomes stronger, making it less comfortable and, crucially, looser underfoot. My trainers start to skid. I'm overtaken by two guys from the British army. One shouts to the other: "There is no way I'm finishing this without you. I'll carry you if I have to." He smiles at me as we pass. "Brutal, isn't it?"
Brutal it may be; it's also spellbindingly beautiful. The savannah is dotted with thorn trees and impala. In the distance are the jagged peaks of Mount Kenya - no snowcap this year; it is hotter than usual - and the Samburu sacred mountain of Lolokwe. As I toil past the halfway point I recognise the spot where, on a game drive the previous day, we had seen a cheetah laze in the sun with her cubs.
The marathon, which is organised by conservation charity Tusk, has raised $1.3m since it began nine years ago. The money is distributed to wildlife and community projects across the country, including Lewa. This year part of the money will also go to the Kenyan Red Cross, after post-election violence at the start of the year left hundreds dead and thousands homeless. The conflict was also damaging to Kenyan athletics. Among those killed were Olympic relay finalist Lucas Sang, and marathon runner Wesley Ngetich, who was shot with a poisoned arrow near the Maasai Mara game reserve. Many others were too afraid to train.
I had no such excuses, but in my training runs I had never managed to run the full distance of the race. Three kilometres before the end, as I run through swampland, my legs become unsteady; I trip and fall. A ranger puts down his G3 rifle to pick me up. My hands and knees are cut. He offers disinfectant, but I am loath to lose time. Instead he goes to help another European runner who has fainted.
I'm still enclosed in the swamp when I hear cheering. Turning into the final straight, I'm greeted by a huge crowd gathered around the finish. Maasai warriors stalk the edge in red shukaa and beads, carrying spears. There is whooping, shrieking and the syncopated beat of a dance tent in the background. I crash over the line, a sweating mix of euphoria and exhaustion.
The first 39 runners on the results board are Kenyan, with the top 10 coming in under two hours 27 minutes, amazing at this high altitude. Despite their convoluted preparations, the last 10 to finish are all from the US. No matter what their time, everyone is in celebratory mood, and after having my knee dressed I join the other runners for a post-race Tusker beer.
Before the partying properly kicks off, the Tusk team offers me a ride in the race helicopter. An elephant, one of 3,000 that have found refuge at Lewa, has been sighted near the track and we must shoo him away. We hover low and close. The great beast turns to face us and flares his ears, but eventually backs down and tramps away. The helicopter lifts, and we watch him rejoin his herd.
Original article published in Financial Times, in August, 2008