LOS ANGELES — The first sign of what is to come at Nerdstrong Gym in North Hollywood is the red welcome mat: It’s in the shape of a Dungeons & Dragons 10-sided die. The equipment inside includes 25-pound steel clubs (for the potions class portion of a Harry Potter workout, among others). A gray concrete wall is painted with pixelated Space Invaders from the 1970s video game. And the gym’s handbook reassures members that workouts can be scaled from Padawan to Jedi Master (that’s Star Wars for pretty easy to really hard).

Since this gym opened in 2013, members — many driving an hour across crowded freeways to get there — have kicked down dungeon doors, defeated the Death Star, raided ancient temples with Indiana Jones and battled Coily alongside QBert, the 1982 arcade game. An Eye of Sauron workout, drawn from “The Lord of the Rings,” features step-ups (Frodo and Sam had to climb a lot of stairs) and sandbags (evoking Sam carrying Frodo up Mount Doom). Every three minutes, when the Eye of Sauron sweeps across the gym, everyone has to drop into a plank position until it passes.

“If I Google ‘God of War workout,’ I get a bunch of workouts that make you look like the God of War,” said Andrew Deutsch, 45, the gym’s founder, referring to a series of video games. “I want to do movements that make you feel like you’re in the game.”

It’s this unabashed enthusiasm for fantasy that has lured, and made regular gymgoers of, geeks whose biggest sweat before joining may have been a strenuous argument about which Teenage Mutant Ninja Turtle is best. It helps that Nerdstrong’s spirit is collaborative. Among the workouts that belly-flopped was a Star Wars one in which the Rebels ended up helping the Imperials because neither side could bear the thought of being responsible for the other having to do 30 extra push-ups for losing.

Since joining Nerdstrong, which costs $20 per class or $150 per month, Derek Housman, 33, has lost more than 65 pounds and can do over 100 strict push-ups in a workout.

Housman walked into the gym depressed and weighing 315 pounds, having been dragged there by a friend he had met while making short films for the internet. Now Housman attends classes five or six days a week, sometimes twice a day, and recently went with another friend to get matching tattoos of Nerdstrong’s logo: a silhouette of a caped hero triumphantly lifting a barbell overhead.

“I didn’t ever think I’d get a tattoo,” said Housman, who is Jewish and grew up believing that his religion forbade such marks. “This is a permanent change I’m doing to my body, but so is Nerdstrong and so is having a community of people who won’t give up on me.”

There are no elaborate sets for workouts; few who attend this gym have trouble summoning the images to mind. Props are used only for athletic benefit. Space Invaders painted on the wall, for example, are set at 8 feet and 10 feet high. They are designed as targets at which to throw weighted balls, for an exercise that may be used as a way to gain entry to the Death Star, or as bull’s-eyes for the boulder supposedly crushing class members in an Indiana Jones workout.

“Some of these younger kids have not seen ‘Indiana Jones,’ and it just drives me batty,” Deutsch said.

Mostly high-intensity interval training, the “gamified” workouts also attract lifelong exercisers who have never felt at home at any other gym.

Lili Wyckoff, a lawyer and onetime college fencer, called Nerdstrong “my version of Disneyland — you’re surrounded by people who are excited by the same things as you.”

Wyckoff, 29, whose workout gear included black yoga pants topped with a bright blue, red and yellow Captain Marvel jacket, said she struggled to motivate to exercise on her own and found the role-playing aspect made her look forward to sweating.

“You end up doing more because it’s not, ‘I have to run 5more meters,’” she said. “It’s, ‘Oh, I have to save this villager.’”

Like many of his disciples, Deutsch is a recent convert to fitness. At 38, he got tired of being out of breath climbing two flights of stairs at work, and began doing CrossFit. He liked some elements — “barbells are really cool,” he said — but after three years became increasingly disillusioned with both coming in last in competitions and what he saw as the program’s one-size-fits-all approach to motivation.

“The onus was kind of on me to enjoy it,” he said. “They’re just running through a system.”

He took to exercising in his garage. Soon after, his Dungeons & Dragons master, whom he had been trying to persuade to exercise, was going through a divorce and came to stay. “I’m not going to do this,” the friend said, looking at Deutsch’s equipment.

So Deutsch, a graphic designer, coaxed him with a dungeon workout, sketching it out on a whiteboard. (“You bust down the door, you fight the monster, you get two minutes to fight the monster, it’s so many reps, and if you don’t win you stay and fight again. If you do, you go into the next room.”) The friend began posting accounts of the workouts on Twitter, and people started showing up at Deutsch’s, wanting in.

“I was like, ‘I don’t understand why you’re at my house when you could be at some of the greatest gyms in the world, but OK,’” Deutsch said.

In spring 2013, he cashed in his 401(k) and with the $40,000 founded Nerdstrong. It is one of several fitness options thriving in this somewhat improbable niche; Nerd Fitness, the online self-described “community of underdogs, misfits and mutants,” says it has more than 40,000 paying members.

During nerd workouts, there is no talk of feeling the burn — only powering up, defeating the enemy or, in the case of the yoga class the gym offers, “filling your mana stores.” Trying to make sure everyone had enough space for a recent workout, Deutsch told the class: “It’s like physical Tetris.”

Let other gyms claim Olympians or movie stars as clients; Nerdstrong’s members handbook insists that Dr. Richard Feynman, the theoretical physicist, “would certainly have been a Nerdstronger and you cannot convince us otherwise.” This may be the only gym on the planet that closes for Comic-Con, and where a workout was paused for the announcement of the newest actor to play the doctor on “Doctor Who.”

Getting dressed up for the gym takes on new meaning at Nerdstrong; it can involve face makeup, hair dye and props. For a Guardians of the Galaxy workout, Andrea Letamendi, 37, dressed as a character named Gamora, complete with red streaks in her hair and green eye makeup. She brought a hat and whip to the Indiana Jones workout, but didn’t wear them to exercise.

“People do get really creative, but we’re here to work out and to work out hard, so you don’t want to wear anything that would compromise your workout,” said Letamendi, a psychologist who hosts a podcast during which she analyzes Batman. “The dressing up is more like a nice punctuation.”