Yes, the name is an overt nod to Jim Jones, the sect leader who steered more than 900 people to suicide in 1978. No, the couple that owns the gym, Lisa and Mark Twight, don’t see anything obnoxious about that. “We knew some people would call us a cult,” Ms. Twight said, “so we decided to own the joke.”

The zealous devotion clients have toward the gym and its fitness philosophy, which turns as much on psychology as it does on physicality, can indeed be a little frightening. Picture Scientologists, except with really big biceps.

One prominent fan is Zack Snyder, the Warner Brothers director whose testosterone-turbocharged “300” became a global smash in 2007. It was Gym Jones, using a mix of power lifting and military-style calisthenics, that whipped Gerard Butler, the star of that film, into loincloth shape.

Superman himself has recently been training here. Henry Cavill, hired to play the title character in Mr. Snyder’s coming “Man of Steel,” arrived with eight-pack abs, or close to it, from training for another film. But Warner brought on Mr. Twight to mold the British actor into a true superhero; the two have been working together since April. “It’s not just about muscles,” Mr. Snyder said. “In fact, that’s the least of it. They have a way of making you find things in yourself, and it’s fantastic.”