How does one distinguish between a grunt and a very deep breath? Must a grunt be “characteristic of a hog,” as one dictionary defines it? And what if there are no patrons around to take offense? What would happen if Monica Seles and Maria Sharapova, known for their noisy exertion on the tennis court, showed up wanting to work out?

Image At Planet Fitness, some members say, they are humiliated for taking their workouts too seriously. Credit... Susan Stava for The New York Times

At Planet Fitness gyms, grunters and other rule-breakers are treated to an ear-rattling siren with flashing blue lights and a public scolding. The “lunk alarm,” as the club calls it, is so jarring it can bring the entire floor to a standstill. (A lunk is defined, on a poster, as “one who grunts, drops weights, or judges.”)

Tim Gunther, a 6-foot, 200-pound firefighter in Poughkeepsie, said he and his colleagues were frequently harassed for “making noises that can’t be avoided” and compared the alarm to a nuclear war siren. “The first time I heard that thing it scared the heck out of me,” he said. “I thought there was a fire, and I’m a fireman. Without exaggeration, I’ve seen them set that thing off on people just for breathing too loud.”

At most gyms, etiquette battles are over loud cellphone conversations, the failure to wipe down machines after use, or standing too close to the treadmill while waiting for a runner to finish. “Telling someone they can’t grunt seems a little rigid,” said Sonny Kim, the general manager of the New York Health and Racquet Club’s branch on West 23rd Street in Manhattan. “I’m assuming most people who have worked out have grunted. I have as well; it’s about physical exertion.”

Several press agents for national organizations that represent health clubs said they could not think of any other gym that had anything resembling a no-grunting policy.

“I’ve never seen any gym that micromanages their customers like that,” said Bernhard Schroeder, a spokesman for IDEA Health and Fitness Association, a trade group. “If they see someone talking, are they going to tell that person they’re disturbing other patrons? It’s wild.”

Grunting can be a nuisance to anyone within earshot, sure, but does it serve any physiological purpose?