The Tenzing-Hillary Everest Marathon is held annually on May 29 to commemorate the first successful ascent of the world's highest mountain by New Zealand explorer Edmund Hillary and Nepalese Sherpa Tenzing Norgay in 1953. It's the world's highest marathon, starting from Everest Base Camp at about 5,400 metres above sea level.
Extreme elevations put the body under tremendous physical exertion. Reduced air pressure and lower oxygen levels at altitudes higher than 2,500 metres can lead to altitude sickness. Symptoms include headaches, fatigue, nausea, dizziness, lack of appetite and poor sleep. In some cases, further complications can develop, and the condition can become life-threatening.
Apprehensive about what lay ahead, I tried to persuade a couple of running and trekking buddies to join the race with me. One said it was too serious, the other said he would die if he tried it - this from two guys who had conquered Kilimanjaro (Africa's highest mountain at 5,900 metres) and finished the 100-kilometre Oxfam Trailwalker in Hong Kong in a respectable 16 hours.
So in May, I found myself as Hong Kong's first and sole representative among 150 international runners who set off on the slow journey to the marathon starting line. Over the next 11 days, and under medical supervision, we trudged about 80 kilometres with a net ascent of 2,500 metres, and altitudes close to 5,550 metres.
A number of athletes were hit by altitude sickness on the way up and had to rest. One seasoned runner who had completed marathons on all seven continents had to be evacuated. Other participants battled with severe coughs and bronchitis.
I experienced shortness of breath and a tight chest. In keeping with my surroundings, I moved at a glacial pace and frequently stopped to rest. Two nights before the race, I woke up with a splitting headache.
Given the tough conditions, I had moments of doubt as to whether I was being foolish undergoing such suffering for a race. I resolved these by telling myself it would be a life-enhancing experience just to reach the start line at Base Camp and enjoy the majesty of the mountains. Prayer and a family photo in my rucksack provided further strength.
High-altitude running is more demanding than normal road racing, as "your heart rate, breathing rate and exertion level will be higher", says Dr Raymond So, sports science and medicine co-ordinator at the Hong Kong Sports Institute.
He says it is much more difficult to run at the Everest Base Camp level because the atmospheric pressure and inspired oxygen pressure are only about half that at sea level. This means a runner who is not acclimatised to the altitude will lose 30 to 35 per cent of his or her VO2max ability [or maximal oxygen uptake] at 5,400 metres.
"Endurance athletes are no less likely to experience attitude sickness than sedentary individuals," he says, adding that given the challenges, completing the Everest Marathon should be considered a "marvellous achievement".
Kenyan Paul Tergat, holder of the world's fastest marathon time from 2003 to 2007, recalls his high-altitude training at Kaptagat near the Great Rift Valley in Kenya: "My body was not used to an altitude of 2,300 metres … The training was exhausting. Every evening I was very, very tired."
The Everest Marathon is certainly not an event for anyone hoping to set a new personal best. The arduous conditions of the race are reflected in the clock, with most runners doubling or even tripling their usual 42.195-kilometre time. The top finishers over the past 10 years have all been Nepalese; this year's winner was Phurba Tamang in three hours, 41 minutes and 31 seconds. I clocked 13 hours, 15 minutes and two seconds.
Bikram Pandey, president of the race organising committee, says that when they started the marathon 10 years ago to commemorate the golden jubilee of the first successful ascent of Everest, they made it known it would be "very special in many ways".
While the number of participants in this extreme event remains relatively small, participation is growing. There were only 29 runners in the first year, but more than 150 runners - including 90 from 15 countries - took part this year. Pandey says the Everest Marathon is steadily gaining in popularity as it is "a unique tourism product".
Retired British auditor David Vaughan, who has completed 280 marathons worldwide, rated it the most exciting run of his life. Race event manager Shikhar Pandey says: "We want to promote Nepal as one of the best destinations for adventure sports."
Leveraging the growing interest in extreme sporting experiences, the Everest Marathon team launched the Annapurna Marathon (which starts at 4,395 metres) this year. Next year, they will hold the first Winter Everest Marathon in December.
High-altitude running appears to be on the rise. An online search shows that in Nepal and India alone, there are at least eight races held at higher than 3,000 metres elevation.
Having completed 22 marathons on five continents, I believe that more runners in Hong Kong are looking overseas for challenging race experiences.
Whether in Nepal or elsewhere, I hope to see more athletes run out of their comfort zones. Expect the unexpected and you'll have the experience of a lifetime.