Marathon running isn’t easy. The mileage, the terrain, the weather and many other factors present challenges for runners who have spent months preparing for the race.

But some runners are trying a different kind of marathon, one that requires them to run hundreds of laps to reach their goal.

There are many variations on these circuit marathons, whether run around an indoor track or at a sports stadium.

Next month, a group of 75 runners will run the 2nd annual Fenway Park Marathon (https://www.redsoxfoundation.org/event/fenwayparkmarathon/), which requires entrants to run more than 100 laps around the famed ballpark. And on Sept. 28, 100 runners (who each must raise $5,000 for charity) will take on the marathon distance at inaugural Gillette Stadium Marathon, held at the home of the New England Patriots (https://www.dmsesports.com/events/inaugural-gillette-stadium-marathon). Both events are organized by Dave McGillivray Sports Enterprises.

Mental strength is crucial for any marathon, but it is especially put to the test when running a circuit marathon, said Thor Kirleis of North Reading, who ran the first Fenway marathon last fall. He finished sixth overall with a time of 3:51:52; the race had 50 finishers.

“The biggest difference in running a traditional road marathon vs. running one on a tight circuit, such as on a track or in a stadium or ballpark is the mental grind later in the race,” he said. “If you thought a road marathon was a mental challenge after mile 18, you’re in for a battle on a tight circuit.

“The way the mental game unfolds is a bit of a roller coaster. You start the race feeling good and fresh and more excited than normal because you know you’re doing something different and even special, as it was for the Fenway Park Marathon last year and the Arena Attack Marathon in the XL Center in Hartford a few years earlier for me.”

At first, a circuit race seems easy. “Laps seem to go very quickly. Before you know it you’re already on lap 20. Laps go so quickly you start thinking the 116 laps of Fenway are too short to make marathon distance,” Kirleis said. “Making it easy to think this way is the fact that you are looping by the exact same point over and over and over, maybe once every two minutes or less, which means you get to see your family and friends so often. At this point you’re so in the moment you’re not even thinking about how many laps you have left.”

That feeling doesn’t last, however.

“But then it changes as you near the halfway point. Suddenly each lap feels as if it is dragging slow and this happens even if you are not slowing down,” Kirleis noted. “Mentally, each circuit of the course feels long. You still see family and friends each lap, and you hear them cheering and shouting; as you slow, there’s no escaping them. You cannot suddenly hide or slip into a zone to pass the miles.”

The repetition can be difficult to handle, especially as the hours wear on, Kirleis said.

“It is easy to check out, to not focus, because you have the draw from your family and friends. Although they give you support, if you are mentally not engaged, it is easy to slow down or even walk or drop out,” he added. “But there’s also a positive to this: If you are mentally engaged, having that support every two minutes upon completion of each lap, this gives you so much motivation to continue on and a reminder to hold onto your pace. That support helps you dig deeper and for longer…so while it is mentally much more taxing than a standard road marathon, the nature of the loops and getting constant motivation can make you dig so much deeper — though this also means it can hurt that much more. To me, that’s the prize—battling through steep hurt and coming away a victor.”

In March, seven runners upped the ante at the 2018 Armory NYC Indoor Marathon World Record Challenge, running 211 200-yard laps at Manhattan’s Armory. Both the men’s and women’s world indoor records were set at the event; Malcolm Richards finished in 2:19:01 (compared to the standard marathon world record of 2:02:57 by Dennis Kimetto) and Lindsey Scherf won in 2:40:55 (compared to Paula Radcliffe’s standard marathon record of 2:15:25).

Compared to traditional marathons, these circuit races comprise a very small niche. But if you’re looking for something different, maybe running a lot of loops is the next challenge for you.