Most often, they run alone, sometimes only hearing the steps of the racer ahead of them and the huffing of the runner behind.
There are no scenic vistas, no cheering crowds, no fresh breezes and certainly no rock 'n' roll bands to provide a boost down the home stretch.
When tower runners (aka stair climbers) race, it's often up gray, windowless, concrete silos where one step leads to another and another and another -- into the hundreds or thousands -- a gauntlet of pain for the lungs and legs.
"It really is pretty desolate and dusty," said Kristin Frey of Schaumburg, Ill., who was the top-ranked U.S. stair climber and No. 2 in the Towerrunning World Cup standings in 2012. "It's not really all that scenic. I think I like that it comes down to being me against the tower. It's myself going as hard as I can for the entire time. Mentally, you really have to focus. You have to be strong because you have no idea where you are in terms of competition."
To PJ Glassey of Seattle, the vice president of the USA Stair Climbing Association (stairsport.com), tower running is the toughest sport he has ever tried.
"It's probably 85 percent mental," said Glassey, 47, who ranks No. 5 in the U.S. this year and was 39th in the world in 2012. "The pain of an endurance run of a marathon or ultramarathon is for sure intense, but it's spread out over a long period of time. With tower running, it's the most intense pain condensed down into eight to 12 minutes."
Yet he gets a high and sense of accomplishment from climbing stairs that he hasn't experienced from anything else.
In fact, Glassey and his girlfriend recently planned a short getaway to Las Vegas not to gamble, drink or see shows, but to run up as many towers as possible in search of that endorphin rush that he calls "way more addicting than real drugs."
"Tower runners are a strange breed," he said.
The first big tower run in the United States was held in 1978 with the Empire State Building Run-Up in New York City. That event now continues as the country's granddaddy race on America's most recognized skyscraper. In February, Australian Mark Bourne pumped his way up 1,576 steps and 86 floors in 10 minutes, 12 seconds -- 39 seconds off the record -- to best a field of 600 runners from 18 nations.
But tower running was born in Europe and it spread more quickly -- and has attracted a bigger following -- across the Atlantic. In Europe, the top runners are pros and can make a living running up stairs. In the U.S., it's an amateur sport where most of the events are fundraisers for charities and just a few award anything more than medals.
The European Towerrunning World Association (TWA) governs the annual Towerrunning World Cup (towerrunning.com) system that incorporates nearly 200 races across the globe and has overseen a ranking system since 2009. Last year, more than 100,000 men and women participated in races, according to Sebastian Wurster of Germany, president of the TWA. In 2013, races will be run in 33 countries.
The USA Stair Climbing Association is aligned with the TWA and ranks U.S. runners and organizes a U.S. Towerrunning Championship in Las Vegas at the Stratosphere Casino, Hotel & Tower. The annual Scale the Strat is a vertical marathon of 108 floors and 1,455 steps that American Kevin Crossman won last year in 7 minutes, 5 seconds -- almost 11 minutes faster than the slowest finisher.
There are a variety of races within tower running. There are the long vertical climbs such as the annual Skyrise Chicago, a race up the Willis Tower (103 flights and 2,109 steps) that draws more than 2,000 runners, and the Hustle Up the Hancock (94 floors), also in Chicago.
But there are sprints, too, such as the 417-step race up the inside of the Revolutionary War monument in Bennington, Vt., that can be done in less than a minute and a half by the elite. Other events, like the San Diego TOWERthon, can be done two ways, either as a 25-floor sprint up the Columbia Center or as a two-hour race in which racers do as many flights as they can.
In recent years, the number of events in the U.S. has almost tripled to about 150, said Glassey, in large part because of the involvement of the American Lung Association, which uses the events as fundraisers. In July and August, three events were on the U.S. schedule: the Fight for Air Climb in Charleston, S.C. (July 20), the Step up for Cancer in Commerce City, Colo. (Aug. 11) and the CF Climb for Life in Raleigh, N.C. (Aug. 24).
"It's amazing how many stair climbs we have to choose from now," said Glassey.
Almost anywhere there are stairs, there can be a race.
Near Spiez, Switzerland, climbers do the Niesen Treppenlauf, racing up the longest staircase in the world. It's 11,674 steps up a service staircase that runs adjacent to a funicular to the top of Mount Niesen. At Radebuel in Germany, competitors in the Mount Everest Stair Marathon do 100 trips up and down 397 stairs (supposedly the equivalent of climbing the mountain).
Frey, who has done races in the U.S., Europe, South America and Taipei says every venue has its challenges.
Steps can be different heights. A few have mass starts -- such as the Empire State Building Run-Up -- with thundering herds and hip checks (though most races send off runners staggered, one-at-a-time). Occasionally, routes will zig down hallways, or there will be a short sprint of 100 yards or so at the start to the stairwell door.
"All the towers are completely different whether you turn to the right or the left," said Frey, 29. "When I did the climb in Taipei, the steps were so steep. I've never climbed in a building like that. … These steps were just huge. That definitely makes it harder."
She did OK, though, finishing third (14:32) in the race up 91 floors of Taipei 101, the city's 1,671-foot downtown tower.
Thomas Dold of Germany is the king of stair climbing with four straight World Cup titles. Australia's Suzanne Walsham is the reigning women's champion, outpointing Frey. Both were also first last year on the Vertical World Circuit, a separate ranking of racers based on eight designated tower runs around the world.
Frey, a runner from her high school days, did 12 marathons between 2005 and 2010 when a friend coaxed her into doing the run up the John Hancock Center tower in 2010.
"It was something totally different and it gave me a new challenge," said Frey, who qualified for Boston 10 times and has a PR of 3:14. "During the actual race, I found out I really didn't push myself as much as I could have."
Frey looked online and discovered there were tower races everywhere.
"I was finding races all over the country and all over the world that I had no idea even existed," she said. "It was like this whole new sport to me."
Since then, Frey has done 10 to 15 races per year. In 2012, thanks to the sponsorship of the company she worked for (which paid some travel costs). Frye tried to win the World Cup championship by competing in some of the biggest races, doing two in South America, two in Europe and the one in Taipei. She finished second in the global standings, but, in the process, earned a victory in the Hancock tower race, a special prize because it had been her first race.
Glassey did his first race in 2007. It was the Big Climb, a longtime annual race up the 69 flights of the Columbia Center in Seattle that draws as many as 6,000 participants. Glassey owns and operates the X Gym in the city and does some intense workouts, so he wanted to test himself.
"When I got to the top, I was really pooped and thought, 'Wow, this was really hard,' " Glassey recalled.
It spurred him to train for it the next year and to put a team together from his gym. He cracked the top 10 in 2008, and his team finished third (it has now won it several times). In 2009, Glassey met a runner from Los Angeles at the Big Climb who suggested he do other races.
"At that time, I didn't know there were any other climbs. I thought that was the only one in the world, like it was just a Seattle thing," Glassey said, laughing.
Since then, Glassey has averaged 12 to 15 races a year. He does it not only for the challenge, but for the exposure for his gym and his training methods, which feature short, intense workouts.
"It's sort of proof my protocols actually work, and they're not just for show," he said.
But, it's an expensive pursuit. It costs him about $15,000 per year.
"It's like any expensive sport, like skiing or scuba diving," Glassey said. "You're going to pay a ton of money to do it. But if it's fun enough, it's worth it, and to me, it's fun."
Ask anyone who has ever run stairs, and they'll tell you it's a killer. Legs turn to rubber, lungs burn and each thigh feels as if it weighs 200 pounds. On long climbs, Frey says she doesn't so much run the stairs as fast-walk them, taking two at a time while using the handrails, too, to pull herself along (as most tower runners do).
New Zealand's Melissa Moon once said that a stair racer's biggest asset is "your ability to tolerate pain."
Even breathing can become difficult, with many regulars fighting "track hack," a condition where breathing comes so hard that throats become irritated, causing coughing and other difficulties. Glassey wears a mask, allowing him to breathe in warmer, moister air and halt the "hack."
Glassey, in explaining what it's like to do a long run such as the 103-flight Willis Tower, breaks it down in detail. By the 10th floor, the legs start to tire. By the 20th floor, the heart hits its maximum rate. Climbers hit their "first wall" at the 40th, but he says it's the "false wall" of the lactate threshold that can be pushed through. From about 50 to 70, the endorphins kick in, and it's cruising time until climbers hit the "second wall."
"And you've got 33 more floors to go," Glassey said. "That's where it separates the experienced runners that are in great shape from the non-experienced runners that are in great shape. The non-experienced runners have to fall off and slow to a crawl and get a crappy time. The experienced runners gut through it and endure the suffering because they know how."
It sounds brutal, but for those who are hooked, they keep coming back. They like the climbs, but they also love the camaraderie with the other climbers, who they meet for dinners and sightseeing trips.
And they even rope their friends and family to join them.
That's what Frey did with her 57-year-old father, Steve, last year for the 94-floor Hustle Up the Hancock climb. They trained together, and he made it to the top.
"I had won the race, but for me, it was more emotional seeing him reach the top and be able to do that," Frey said. "That meant a lot having him there. I was kind of more excited about that."