Christian Stangl, the Skyrunner

Decked out in just training clothes and cross-country shoes, Austrian alpinist Christian Stangl didn't look as if he was about to embark on an expedition to climb Mount Aconcagua, the highest peak in the Americas, in 2003.

On the morning of his ascent, he met some other climbers preparing for a conventional three-day expedition. Bewildered by his dressed-down appearance, they asked him his plans. "I want to go up and down in five hours," he told them. Stunned, they turned away without a word.

"They must have thought I was mad," Stangl muses. In the end, he needed only four-and-a-half hours.

Three years later, carrying just a ski pole and a small backpack filled with carbohydrate gels, salted cookies and rosehip tea, Stangl summited the tallest mountain of them all, Everest, in under 17 hours, a new speed record.

Stangl's climbing ethos has been described as pure mountaineering, but he calls it skyrunning. With hardly any equipment, no supplementary oxygen and no company, his approach is to insure against the grave dangers of high-altitude climbing by traveling light and getting up and back down the mountain before the weather deteriorates or his body begins to struggle from oxygen starvation.

Stangl is preparing to scale a mountain fewer than 300 people have ever scaled

Not only is the speed at which he climbs unprecedented, but this revolution in Free-Solo mountain climbing which he has brought about also has environmental advantages. Where traditional methods often leave the remnants of camps, oxygen tanks and other hardware on the mountain - a problem particularly bad on Everest - the skyrunner leaves only other climbers in his wake.

In December 2007, he completed his Seven Summits Speed Tour, to the highest peaks on every continent, in just over 58 hours. By way of comparison, other climbers take an average of 500 hours. To climb so quickly, the Austrian takes on a training regime which requires he maintain a pulse rate of 164 beats per minute for 20 hours straight.

To do that, he drags 'the beast', a 40kg truck tyre behind him while running uphill. His most important endurance test though, is one of concentration and Stangl finds reciting foreign languages to be a useful tool - Russian for the strength and energy to tackle heavy snow; English to focus the mind in potentially fatal situations.

Now, Stangl is preparing to scale a mountain which fewer than 300 people have ever scaled, and which has claimed a life for every four successful summits. K2, the world's second-highest peak, has been dubbed 'The Savage Mountain' for its hideous difficulty and ferocious weather. Even now, years go by without anyone reaching the top.

Stangl did try to climb K2 in August last year, but he had to abandon his attempt at 8,200m after the worst climbing disaster this century claimed eleven lives. Arriving 30 minutes after the avalanche that caused the tragedy, Stangl helped co-ordinate a rescue effort in which two sherpas died.

A year on, and a hundred climbers have gathered at K2's base camp with a wave of expectation that somebody could be about to complete the first ascent since that tragedy. Stangl intends to be the first man up, and to do so quicker than anyone has in the past.

But already, only last week, an Italian skier was killed on the mountain. This meant that Stangl's Italian teammates, who he met in Islamabad and then traveled with to base camp returned home, making him the first one-man group ever seen on K2.

If the risk is too great, Christian will have to find his own route to the top

His task has been made even harder by what caused last year's disaster - the splitting of the serac, an overhang of glacial ice, in a steep corridor near the summit known as 'The Bottleneck'. This split destroyed the fixed ropes which help climbers up the normal Abruzzi Spur route, and it may have blocked the route entirely.

This means that, to determine the condition of the serac, Stangl will either have to climb to 8,000m on Broad Peak, the mountain opposite K2, to get a full view of the ice-cliff, or climb up directly beneath it to assess, in his own words, "whether she will let me pass". If the risk is too great, he'll have to find his own route to the top.

Speaking before he left, Stangl admitted to a nervous excitement, and seemed to suggest K2 was like a tempestuous and unpredictable mistress. Questioned about his prospects on the mountain, he replied simply: "It's up to her."