The arm regarded by many as the strongest in New York measures 39 inches from neck to wrist, with biceps the circumference of a football and skin spray-tanned to a similar leathery brown. Even in repose, its snaky veins swell to the surface, masked only by a tangle of tattoos. Six days a week, the arm spends two hours in the gym, sculpting itself to perfection. It can curl 100-pound dumbbells with ease. It requires specialized tailoring. It has saved lives.

So the man attached to the arm, a 6-foot-5, 275-pound behemoth named Mike Ayello, was more than a little surprised one Saturday afternoon in August to see his prized limb pinned against the table of a Long Island sports bar in a matter of milliseconds.

Mr. Ayello works as a New York City firefighter for Ladder Company 135 in Glendale, Queens, but for seven years, he has moonlighted as a professional arm wrestler. The pursuit is no mere hobby: Arm wrestling has become big business. Capitalizing on AMC’s 2014 reality television show “Game of Arms,” the World Armwrestling League signed a broadcasting deal with ESPN. The popularity of the sport has been growing ever since, attracting a burst of fans and corporate sponsors. Many of the game’s top “pullers,” as arm wrestlers are called, now train with the urgency of Olympic athletes for tournaments that can net them tens of thousands of dollars in a single day. Still, for a great many competitors, the money is hardly the point.

“There’s no feeling like taking a guy down with my arm,” Mr. Ayello, 39, said. “It rips their soul away. It emasculates them. I like doing that to people.”

Even as arm wrestling’s financial stakes have risen, the sport’s central appeal remains the same: the chance to capture a moment of personal glory, no matter how fleeting. Like Mr. Ayello, most pullers balance more traditional jobs with training and tournaments. But unlike Mr. Ayello, many buck the sport’s typecasting.

Competing with the firefighters, police officers and gym owners are accountants like Steven Green, high school math teachers like Heidi Cordner, psychotherapists like Ron Klemba, musicians like Henry Bliley, organic farmers like Barbara Schlegel, programmers like Greg Arnold and stay-at-home mothers like Kristen Kent. Among arm wrestling’s most intimidating female competitors is Joyce Boone, a home health aide and grandmother with diabetes and hypertension.

Not all arm wrestlers bear the honed physique of a typical athlete. Weighing around 400 pounds is Shawn Lattimer, a mechanical engineer from southern New Jersey who has the word “Power” tattooed across his right forearm.

And Kaue Teixeira, a construction worker with the lanky build of a fashion model, said his colleagues were stunned to discover his weekend avocation. “I like taking down guys who are bigger than me,” said Mr. Teixeira, 27. “It’s the best part of my week.”

With his cartoonishly hulking physique and swaggering machismo, Mr. Ayello has become something of an ambassador for arm wrestling, earning a Top 5 ranking nationally, according to the World Armwrestling League, and titles like King of Arms.

The event on Long Island, which was held in Farmingdale, was Mr. Ayello’s first attempt at staging a competition of his own. He brought in dozens of amateurs and pros from across the country and fashioned a set of medals emblazoned with a caricature of his upper body, shirtless and flexing. The marquee match pitted him against another firefighter: Casey Coley, a 260-pounder from Alabama nicknamed King Kong.

Falling behind 1-0 in a best-of-five contest, Mr. Ayello grimaced but did not despair. Mr. Coley was able to take him down so quickly in the first round as a result of finer technique, not superior strength. Though brawnier pullers tend to fare well, success largely rests on strategy — the angle of the tug, the timing of a surge, the precise positioning of each finger.

In this bout, the difference between an advantageous grip and an unfavorable one came down to millimeters, prompting a negotiation between the pullers that rivaled the Yalta Conference. Four solemn referees were brought in to scrutinize the clenched hands before each round. Growing restless, the beer-swilling crowd urged on its local hero. “Rip his arm off!” one yelled at Mr. Ayello.

He refused to surrender. All week, he had been preparing for the match, doing static holds with a series of exercise bands tied to a pole in his backyard. To maximize his energy, he spent the previous day gorging on pizza, pasta and pancakes — 20,000 calories total.

Carbohydrates and adrenaline surging through his body, Mr. Ayello reconsidered his positioning and mounted a purposeful comeback. Three takedowns (and several heated disputes) later, he was declared the winner, by a score of 3 to 1. The spectators erupted in applause, and Mr. Ayello indulged them with one last flex of his champion arm.

The next day it would be hidden under the sleeve of his firefighter’s uniform.