Inside Barry's Bootcamp, the Gym That Kim Kardashian Built

Dim lights. Loud music. "You are beautiful" proclamations. Kim Kardashian.

This is not your average workout.

Welcome to Barry's Bootcamp, the Hollywood exercise program that's taking hold all over the world, merging the gym and the nightclub into one massive, mind-body sweat session. Actors and actresses have relied on founder Barry Jay's combination of interval training and resistance routines for years, including Sandra Bullock, Jake Gyllenhaal, Julia Roberts and Christina Applegate.

Then came Kim.

"Kim has had the most powerful effect out of anyone we've ever had," said Barry's Bootcamp COO Joey Gonzalez. "She's just a walking advertisement. There's mass appeal now. I'm grateful to her."

PHOTOS: Inside Kim Kardashian's Favorite Gym.

The reality TV personality has been photographed leaving Barry's Bootcamp studios in Los Angeles and New York City dozens of times, most frequently in the run up to her August wedding. If her legendary backside encased in spandex isn't endorsement enough, there are her tweets:

Sept. 16: "Just had the best workout at @BarrysBootcamp! My arms are shaking! U know that feeling when u work out so hard...love that feeling!"

Sept. 14: "I am sooo happy that Barry's Bootcamp just opened in NYC! This changes everything!!!"

For the 13-year-old chain of gyms, Kardashian changed everything. Barry's Bootcamp's fifth club, its first outside of California, opened in New York City in June. Studio No. 6 landed in Bergen, Norway soon after. Gonzalez has just signed a deal that will bring Barry's to Nashville, Tenn. He plans to head to London, England next. With nearly 40,000 members in the U.S., Barry's reach extends beyond celebrities.

"I've trained people that have lost as much as 140 pounds doing this," Gonzalez said. "Most of our members are coming to be put in a position where they wouldn't otherwise find themselves. They're mostly type-A personalities. If they did the research and they knew more about fitness they could easily do this on their own, but they don't have that time or discipline."

Kardashian declined to comment for this story through her publicist. But one need only Google photos of her in her strapless Vera Wang wedding dress and honeymoon two piece to see why she evangelizes the workout. Four to eight minute long treadmill intervals followed by the same amount of resistance training repeated two to three times in one hour will whip anyone into red carpet shape, if they can get through the ordeal without face-planting on their mat.

"It's similar to a caveman workout," Gonzalez said. "We used to sneak up on prey and sprint and grab a rock and smash it. The human body never ran long distances for five miles, which most people will do -- they'll turn on the treadmill or go to the park and run at 6.5 miles per hour for an hour. That's great, but that's not what's going to make you ripped."

Beyond the workout, Barry's emphasizes atmosphere. Purple and red lights flood the NYC studio. Locker rooms are stocked with Malin + Goetz beauty products. Rihanna, Britney Spears and Beyonce cry out at levels so loud, the front desk offers earplugs. Beaming instructors bounce around the room as if fueled by IVs of espresso and sunshine. Instead of a militaristic barking of orders, they coo instructions and encouragement into their concert quality headsets: "You can do this! You rock! Just 10 more seconds! Are you feeling it? I know I am!"

Clients respond -- at a recent New York City session, one member began belting out the chorus to Kelly Clarkson's "Since U Been Gone" while doing a set of skull crushers.

"A big part of what we do is fun," said Gonzalez. A former actor, Gonzalez, now 33, began working for Barry's in 2004 after he attended a class and "fell in love with it." "We look for entertainers," he said. "Often times, the personal trainer who has the best reputation and might have a ton of knowledge just falls flat, isn't fun and can't carry a class."

Fun, yes, but at a price: Barry's New York location charges between $32 and $19 per class. While many NYC gyms range from $50 to $100 a month, Barry's monthly membership currently costs $450.

And then there's the physical toll. All the top 40 hits, celebrity work out partners and cheerleader instructors don't make sprinting at nine miles per hour at a 10-percent incline any less grueling, as this reporter attempted to do at a New York City class last week. But then, that's the point.

"I've done about 120 marathons, and if you're doing a 10-percent grade at nine miles per hour, there are world class athletes that would have a problem with that," said Michael Dupper, an assistant professor in the department of health at the University of Mississippi. He's never been to Barry's Bootcamp but noted, "the premise seems pretty sound."

"These people are going to get a tremendous workout," he said, "if they can survive."