The New Workout: Muai Thai Without the Bruises

The music is clubby and pop-centric (Rihanna, Miley Cyrus), and the crowd is heavily female. A recent weekday class was sprinkled with men, who, Mr. Glazer said, are increasingly in attendance.

One of these guys was Michael James, 41, a personal concierge. Mr. James said he started working out at Shadowbox NYC shortly after it opened, hoping to lose weight, and he has gone there twice a week ever since.

“In 45 minutes, I get a workout that could take easily three hours to do elsewhere,” Mr. James said. “The first 5- or 10-minute warm-up here, by the time that’s done, I’m almost drenched.”

He said he has lost eight pounds since making the commitment, and results like his are drawing a crowd. Shadowbox NYC has signed a deal to open a second location in Dumbo, Brooklyn, practically around the corner from Gleason’s Gym.

Gleason’s got its start in the Bronx in 1937 and has been in Dumbo since 1984. Name a fighter of any regard and if they have trained in New York, they have likely trained at Gleason’s: Muhammad Ali, Mike Tyson, the two Sugar Rays (Leonard and Robinson).

Gleason’s is dusty. There is no music. The soundtrack is the whirring of jump-ropes and the whomp, whomp, whomp of fighters laying into heavy bags. There is no Pabst Blue Ribbon, no kale juice. If you need refreshment, hit the snack bar for the beef patty or a bag of Cheez Doodles.

Mr. Silverglade said he is happy to welcome the fitness-centric boxing gyms into the fold. “These gyms, as far as I’m concerned, are a good thing,” he said. “The more people that know about boxing, the more people that come into a boxing gym, the better off we are.”

He reasoned that some of those interested in boxing-as-workout will get more serious about their hobby, and that is when they find Gleason’s.

“I have people come in and say, ‘I want to get in shape, but I don’t want to hit anybody, and I don’t want to get hit.’ And the reason why I laugh at them” — he smiled — “is because boxing is a very, very addictive sport.