For models, the former boxer Michael Olajide Jr. is the heavyweight of trainers — the go-to guy for girls who have to get runway-ready in a hurry.

For this fashion week, he trained some 15 models needing to “sleekify,” as he called it, to squeeze into sample sizes. (Most common problem: the hips.) In preparation for last September’s shows, roughly another dozen catwalk hopefuls hit Aerospace High Performance Center, the spare, airy gym in the West Village that Mr. Olajide owns with the former ballerina Leila Fazel.

Mr. Olajide’s not-a-dry-shirt-left-in-the-room workouts feature rapid-fire choreographed punching sequences (clients punch the air, not one another’s lucrative faces), mixed with jump-rope intervals not seen on any playground. One example: a riff on speedskating that requires landing with one heel crossed behind the opposite leg. Classes can sound like hailstorms, the red jump ropes thwacking the floor. The three-quarter-pound ropes are nicknamed the Rainmaker, for their sweat-inducing potential.

“I like to say there’s no such thing as cold fusion,” said Mr. Olajide. “You’ve got to get your body hot if you want to burn calories and lose that weight.” He contends that jumping rope gets the body moving faster than it can with any other exercise, turning the metabolic oven “up to grill.”