Nearly two decades ago, Britney Spears had one goal — to be, quite literally, stronger than yesterday. Celebrity trainer Bobby Strom, who worked with Britney in her late teens and early 20s, can attest.

“Right off the bat, she was like, ‘Hey, this is what I’ve got to do: I’ve got a Pepsi campaign, I’ve got the VMAs, I’ve got the cover of Rolling Stone coming up. I really want to get into the best shape that I can in this amount of time,’” the seasoned fitness guru tells Life & Style in an exclusive interview. “And she was in it to win it from day one.”

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Bobby (center) with Britney and her then-boyfriend, Justin Timberlake, in the early 2000s. (Photo Credit: Courtesy of Bobby Strom)

After meeting Bobby through a mutual friend, music producer Brian “BT” Transeau — the mastermind behind ‘NSYNC’s “Pop” and Britney’s “Before the Goodbye” — the iconic entertainer, then 18, started breaking ground on what many consider to be her best body ever. Just months later, the superstar unveiled her insanely fit physique (expertly sculpted by Bobby) at the MTV Video Music Awards in September 2000.

During a particularly sizzling medley of “(I Can’t Get No) Satisfaction” and “Oops!…I Did It Again” at the annual awards ceremony, Britney made the world collectively gasp when she tore off her tuxedo to reveal a skin-baring, sparkly nude ensemble. Images of the pop princess (and her enviable abs) from that performance remain the definition of #bodygoals to many modern gym enthusiasts.

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(Photo Credit: Getty Images)

Bobby admits that clients still ask for a mid-section like Britney’s from time to time. “I just entertain it with a smile,” the bodybuilding champ tells Life & Style, adding that his famous trainee’s taut tummy was the result of hard work and dedication. “If you really want to be as fit as Britney was when I was working with her, you’ve got to put in the work like she did. She wasn’t messing around.”

Over the next year, the blonde beauty continued to work harder than ever during her hour-long sessions with Bobby. While she proudly flaunted the fruits of her labor during her memorable Pepsi campaign and on countless magazine covers, Britney wanted to turn up the heat for a very special — and sexy — project: the music video for “I’m a Slave 4 U,” the lead single from her self-titled third studio album. And, of course, she wanted to make sure she was snatched AF when she performed it for the first time (with a snake!) at the 2001 VMAs.

“When Britney was going to do the ‘Slave 4 U’ video, it was all just sweaty and sexy and she killed it because she was really confident about her physique. She wasn’t apprehensive or holding back one bit. She knew she looked incredible,” Bobby tells Life & Style of the chart-topper’s increased self-esteem. “In the months leading up to the performance and video for ‘Slave,’ she was totally dialed in. You saw her confidence in her mannerisms. Like, when she danced with the snake — you could see the fire inside her. She felt fierce. She was fearless.”

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(Credit: Giphy)

Indeed, during her 2001 episode of MTV’s Diary, Britney said that breaking a sweat with Bobby always left her in the best of moods. “When I get up in the morning and I work out, I have more energy throughout the day,” the Mickey Mouse Club alum explained at the time. “I just feel better about myself.”

So how exactly did Britney achieve such a breathtaking belly? “We did somewhere between 750 to 1,000 variations of crunches a day. We would do intervals. We’d start off on the treadmill running, and then she’d go to the mat and do bicycle crunches, hitting the transverse abdominal wall, engaging the obliques,” Bobby tells Life & Style of Britney’s core-focused workouts. “So we’d do a combination of crunches and in between, we’d focus on light weight training. For instance, I’d have her do bicep curls, kickbacks for the triceps, and lateral raises.”

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(Credit: Giphy)

“We never did anything crazy weight-wise because she also had the genetics where she could build muscle very easily, and she didn’t want to get bulky. With Britney, it was all about tightening it up,” the former NYPD detective — who’s trained a myriad of stars, including Scarlett Johansson, Ryan Reynolds, and Jessica Biel, among others — adds. “Before the acronym HIIT came around, which is high intensity interval training, I realized that I’ve actually been doing it for years. And I really kind of perfected it with Britney. It was what we did every day. Britney was a great athlete.”

If you’re brave enough to give Britney’s ab routine a try, follow along with Bobby’s wife and business partner, Alicia Strom — together, they operate Strom Fitness and Massage and regularly share exercise tips on their YouTube channel — in the video below.

Bobby tells Life & Style that your body can transform in as little as 90 days if you remain committed and consistent à la Brit-Brit. “There are three things that play a big part in it: genetics, how strict and dedicated you are with the nutrition part of it, and then also how consistent you are with working out,” he says. “If you stay consistent, say you do it five days a week, and then you eat relatively well, I would say you’ll start seeing results in 90 days.”

Although Britney, a practiced dancer and one-time competitive gymnast, had no problem hitting the gym seven days a week, Bobby says that he had to help the athletically inclined singer adjust her eating habits. The hard-muscled hunk stresses that nutrition and exercise are equally important — which Britney soon figured out after teaming up with Bobby.

“Britney came from Louisiana. She was used to home-cooking — gravy, biscuits, fried foods. So, at that time, she was like, ‘What do I do? My mother, [Lynne Spears], does all the cooking.’ So I had to go over all the cooking with Britney’s mom and say, ‘You’ve got to cut out the gravy and cut out the biscuits and go with this. No mashed potatoes. Replace those with steamed vegetables. Let’s incorporate salads with just oil and vinegar,’” Bobby recounts. “Instead of putting her on a strict and rigorous diet, it was just about making changes and preparing the food differently. I tried to make the foods she was used to eating healthier or more complex. It was just cutting down on the calories and the fat calories, which made all the exercise worth that much more.”

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Britney may not do 1,000 crunches in one sitting these days, but it’s obvious that she’s still a slave for fitness. The now-36-year-old mom-of-two — who shares sons Sean Preston, 12, and Jayden James, 11, with ex-husband Kevin Federline — frequently puts her eternally toned figure on display via Instagram. Bobby tells Life & Style that he couldn’t be more thrilled to see that the Grammy winner, who’s currently dating 23-year-old fitness model Sam Asghari, is prioritizing her health again.

“I’m glad to see how well Britney is doing. Her body looks incredible, but she also looks really happy. She truly is a nice person, a great person, a talented person — and it’s so great to see her back on course and reel it back in and get back to the level she was at before she kind of got all sidetracked. It’s nice to see someone get back on the right track and get back to something that makes them feel good,” he says of the Las Vegas headliner, who wrapped her four-year Piece of Me residency on Dec. 31. “When I trained Britney, I knew that performing and working out made her feel good, and it looks like she’s been doing a lot of both lately.”