Trainer Stephen Pasterino first called his signature class “Thigh Gap Thursday” as a joke.

The founder of Bowery fitness studio Bodies by P had been trying to figure out how to best market his leg- and butt-focused workout, which he claims can give his clients a gap between their legs when they stand with their feet touching — a controversial social-media trend and a near requirement for the scores of models whom Pasterino trains.

“It’s now my busiest class,” he says. “Every Thursday is packed.”

Word of the class soon spread beyond his downtown, in-the-know client base, he says. “We put it on social media, and now we have girls around the world who message us and say, ‘I just want a thigh gap, how can I get one?’”

The thigh gap became a point of obsession around 2013, the year that a book called “The Thigh Gap Hack” was published. Instagram was just blowing up at the time, and the term took off, with scores of women and teen girls tagging their pictures with #thighgap. Model Cara Delevingne’s thigh gap even had its own Twitter account.

Far more disturbing, though, were the women commenting “goals” on pictures of particularly hollowed-out legs.

The thigh gap soon became synonymous with body dysmorphic disorder. Instagram disabled the #thighgap hashtag in March 2014, and more body-positive messages have since become in vogue on the site, such as #effyourbeautystandards and #everybodyisbeautiful.

Now, with the popularity of the class, the term has reared its ugly head again.

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“None of these girls are happy with what they’ve got,” says Pasterino. “But I can see where their bodies can go.”

Given that most attendees are model-like in physique, the messaging behind “Thigh Gap Thursdays” is in stark contrast to the “strong, not skinny” ethos promoted by workouts such as high-intensity interval training and CrossFit.

“When you’re pursuing something unattainable, it’s just going to lead to low self-esteem and beating yourself up,” says Kimberly Hershenson, a Midtown-based therapist who specializes in eating disorders. “Working out should be about wanting to be healthy. If your goal is to be fit, toned, muscular, a thigh gap is not going to help you reach that goal.”

Hershenson warns that a class solely focused on the creation of a thigh gap can lead to perfectionism and, in turn, eating disorders. “Where’s it going to end?” she asks. “When you have the biggest thigh gap in the class?”

Pasterino, 30, says he’s gotten some flak for his social-media posts, which usually include the hashtags #thighgap and #thighgapthursday, along with, bizarrely, #lovemyself and #allbodytypes.

“We get negative stuff like, ‘Oh, that’s bulls--t. Body image and stuff,’” he says of the Instagram comments and direct messages he’s received.

Despite the blowback, Pasterino insists he’s simply giving his clients what they want.

“I’m so focused on butt and thighs because that’s what everybody wants. I ask the girls what they want to do before every class, and they all say, ‘I want to tone my inner thighs, I want my butt lifted.’ ”

When you’re pursuing something unattainable, it’s just going to lead to low self-esteem.

 - Kimberly Hershenson, a Midtown-based therapist
Julia Kudryashova, a 24-year-old former college swimmer who works in insurance, is one such client.

“I’ve felt so much taller and longer and leaner, and I’m seeing so much definition,” says Kudryashova, noting the idea of a thigh-gap workout was “definitely” appealing. “That’s every girl’s draw — you have to have a thigh gap!”

Pasterino hit upon his method while studying physical therapy. He realized that small, stretch-like movements could target leg muscles that other workouts leave untouched, and that opening up the hips was the key to firing up butt muscles that would otherwise be frozen in place.

After two years of teaching classes — and building up his model client base, which includes Dree Hemingway, Maryna Linchuk and Blanca Padilla — at downtown’s modelFIT, Pasterino left to create his own physical-therapy-influenced studio, Bodies by P, in May 2016. Classes cost $36.

Most of the women whom Pasterino trains are trim already, but feel like their legs could be slimmer and their stomachs and arms tighter, all in the pursuit of perfection.

“Often, I’m going in and trying to help these girls lose weight when it seems like there’s no more weight to lose,” he says. “So I say, all right, let’s go in and see if we can dig up a few pounds. And it makes an amazing difference.”

Take Megan Dalke, a 23-year-old Wilhelmina model who started training with Pasterino in November. “I noticed within three weeks that my legs looked longer, and not as swollen as they’d usually be [from working out],” she says. “I look like I grew an inch ... I swear by it now, and I tell all models, you have to come try it.”

But despite the lanky limbs on display in his class, Pasterino insists his method works for anyone.

“I need more overweight people,” says Pasterino. “That’s something I need to work on.”

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