Jennifer Lopez's Trainer Explains How She Got Her Incredible Body: 'She's Got Crazy Discipline'

How does Jennifer Lopez get that incredible body — at 48? A mix of excellent genetics and serious dedication.

“She’s amazing at everything,” her trainer David Kirsch, the owner of Madison Square Club, tells PEOPLE. “She’s genetically blessed, she’s physically gifted with an incredible amount of physical energy, but also this beautiful amount of mental and emotional energy.”

“She’s very connected to her body, and she’s got crazy discipline. And I’m not just saying that — it’s a pleasure to work with someone who is as dialed into her overall wellness as Jennifer is. When she shows up and I get 500 percent. There’s no phoning in the workout.”

Kirsch puts Lopez through a full-body circuit workout when they train together a few times a week at his New York City studio, utilizing stability balls, resistance bands and medicine balls.

“I’m not going heavy on the weight with her, but I keep the circuit up and the intensity up and the cardio up,” Kirsch explains. “It’s about shaping and toning and sculpting. So it’s not a traditional strength workout and it’s not a pure cardio workout. It’s sort of a mix of both of them.”

“And Jennifer’s in great cardio shape,” he adds.

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Kirsch thinks of a rough plan for their workouts before Lopez arrives, and changes it up to fit her needs. Each class starts with a warm-up, and then Kirsch goes through a few of his “signature moves” like the platypus walk she did on Friday.

“I love that one for Jennifer because it focuses on her inner thigh, works on her butt, there’s a cardio element there because of the pace at which you’re going back and forward gets your heart rate up. So it’s a move that delivers right away,” he says. “You’ll feel it immediately.”

And when Lopez comes in, she’s not terribly picky about the music.

“She goes with what I have,” Kirsch says. “A little hip-hop, some beats, some energy. Every now and then we laugh when one of her songs come on, and I promise we don’t pre-arrange it!”