The number of extreme trail runners is on the rise, particularly in Asia.
CNBC attended HK100, an annual race in Hong Kong, where participants from around the world gather to run 100 kilometers, slightly more than 62 miles.
If that sounds like a lot, it is. Even the fastest runners took around 12 hours to complete the course, with the cut-off time being 30 hours.
John Ellis, an investment manager based in Hong Kong, has formed an obsession with ultramarathons, running in 17 races in the past year alone. He said that's amounted to running more than 870 miles just in competitions – which is greater than the distance between New York and Chicago.
"You get this sense of euphoria. I love the challenge. You're one with nature," he said. "It just grounds me and centers me. It's my meditation."
He's so obsessed with the sport, he even co-founded, T8, a Hong Kong start-up which makes running gear for long races like ultramarathons. One of its products, for instance, is a pair of shorts with an integrated running band for storing necessities like a phone and keys.
Ellis is one of about 1,800 runners who competed in HK100, which has grown massively since it started. In its first year, organizers said they struggled to get 200 runners to compete. This year, however, they received more than 8,000 applications for the less than 2,000 spots available.
The demand for extreme races has surged over the past decade. The number of trail races in China, has gone from just two in 2009, according to Sina Sports, to 457 by 2018.
"It's a relatively new sport in Asia and people are discovering all this different landscape," Janet Ng, the founder and organizer of HK100 said. "It is growing exponentially."
Ellis, meanwhile, attributes much of the ultramarathon growth to rising interest in fitness.
"The world's trying to get fitter. You have all these people looking for the next sport and trail running, for me, is just the next logical place," he said.