This weekend, 500 endurance enthusiasts are signed up to participate in a “virtual” marathon, which is being held for the first time by the New York Road Runners organization. The registrants, each of whom has paid $100 ($120 for nonmembers), range from age 21 to 67. They’ll be running in 28 countries and 39 U.S. states, from Florida and California to New Jersey and New York.

Once they finish the mileage, logged through the Strava app (it must be outside, not on a treadmill), the runners will earn a real medal, specially designed for the virtual race. Even better, they’ll receive guaranteed entry into the 2019 race.

The existence of such virtual races underscores the rising global popularity of running as a sport—according to Statistica, the number of overall participants in the U.S. has risen 44 percent since 2006, to 55.9 million people last year. Because races through major cities are capped for security and logistics reasons, however, trying to get a spot in any of the popular marathons has become more about luck than speed.

About 50,000 people will run the New York City Marathon this Sunday, but most of those spots are earned through charity fundraising or running other races to qualify. Only 15,500 spots in the race are designated for general entry, and roughly 105,000 people applied for the lottery this year. Likewise, the 2019 Tokyo Marathon, to be held in March, received more than 330,000 general entry applicants for its 27,370 available spots. The London marathon, held next April, received a record 414,000 applications for 40,000 slots, according to Ryan Goad, a spokesman for the event.

The virtual marathon is organized through Strava Inc., whose app began in 2009 as GPS-tracking software for cycling but now counts runners as its fastest-growing group of users. With 35 million participants, it’s become the platform of choice for New York Road Runners as well as Lululemon Athletica Inc., which has the largest running club on the service.

For Lululemon’s Ghost Race series earlier this month, the brand held virtual runs in 12 cities across America and registered 35,000 people, up from 1,200 who joined in when it premiered in 2016. Lululemon spokeswoman Erin Hankinson says the brand is teaming up with Strava in January to host its third annual 40/80 challenge, where participants can choose to run 40 or 80 kilometers over a two-week period.

Going virtual is a new way to get interested marathoners involved, says Michael Capiraso, chief executive officer of New York Road Runners. “We continue to look at how we can engage with people outside of New York City,” he says. This year has been the “beta year” for testing virtual races: In all, the organization has 10 virtual races on the schedule in 2018, and more than 15,000 people have finished the first seven so far. Last week the nonprofit added another first: the Virtual Turkey Trot 5K, to be held on Thanksgiving Day.

According to Strava, this is the first virtual marathon of its kind. Participating runners will have the first four days of November to complete the distance in a single shot. After it was announced, the virtual race sold out in a “matter of hours,” says David Lorsch, Strava’s vice president for strategy and business development. “We haven’t done anything like this, where you have to run a marathon in a single session.”

Boston’s marathon, which selects runners based on qualifying times, has reduced those times in response because of high demand and growing interest, says Lorna Campbell, spokeswoman for the Abbott World Marathon Majors, which runs a series promoting the “big six” marathons. But the company hasn’t seen anyone else follow New York’s lead in offering a virtual race as a qualifying factor.

At least not yet. But the Road Runners are adding more virtual options next year, starting with another New Year’s challenge, Capiraso says. And Strava is already talking to other running outlets about expanding their virtual offerings. “I think this concept has legs,” Lorsch says.