For the last two years, Raymond Wilburg, 27, has been training hard at Gleason’s Gym in Brooklyn. At first, it was for fitness. “It’s therapeutic,” he said. “All of the world’s problems, whatever I have outside of the boxing gym, it just falls away.”

Then the workouts grew more intense, and he began sparring more frequently. Soon Mr. Wilburg, who grew up in Crown Heights, Brooklyn, and works in a Verizon store, started fighting in amateur bouts, late start be damned.

In every corner of Gleason’s, men and women were sweating away. Trainers held mitts to fighters, swatting at them, egging them on. Two men in their 50s went at it in one of the three boxing rings.

Bruce Silverglade, who has owned Gleason’s for 35 years, said his membership is larger than it has ever been — and a majority has no interest in taking a jab to the face. Of the 1,200 people who pay the monthly $95 fee, Mr. Silverglade estimates that 300 are training to fight. The other 900 are there for the workout.