On January 5th, personal trainer Kayla Itsines put out a call for women everywhere (or at least women on Instagram) to join the #KaylaMovement. The 24-year-old had been selling her workout, the Bikini Body Guide , or BBG, as an e-book for the past year and using her Instagram account to motivate current clients and attract new ones. She decided to kick off 2015 by formally inviting her massive Instagram following , which currently tops out at nearly 3 million, to do her personalized, rigorous workout routine along with her.

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"There is no competition here, there are no winners or losers," Itsines wrote in the caption. "We are all here to support each other and show our progress. We as a team are going to not only motivate each other, but inspire the world. If there was ever a time to make a difference, to push your body and to be the fittest, healthiest, and strongest you’ve ever been. That time is now."

Maybe it was the inspirational quotes, the photos of her washboard abs, or the countless Kayla devotees that already proliferate on Instagram, but Itsines’s New Year's call did not fall on deaf ears. Hundreds of thousands of more women have joined Itsines’s Instagram community since January, adding to her already massive global network.

Social media fame isn't particularly rare these days, especially in the fitness world. You’ve got the Jen Selters of the world who gain followers one belfie at a time and the hardcore yogis who build careers from their accounts. But the people in the community Itsines has cultivated don't just scroll through her feed and like her posts: they get involved. Hitting the gym hard, they actually work out together following the same BBG schedule, using hashtags and commenting on each other's photos to keep up with each other's progress.

The hashtag #BBG has been used over a million times on Instagram, at a rate of one post every thirty seconds. Other hashtags like #KaylasArmy, #thekaylamovement, #thek2movement, #deathbykayla, and #kaylaitsines are also rampant. Stumble upon any of these and you'll fall down a rabbit hole of Kayla fanatics—all female —who post transformational photos, diet plans, meal spreads, and fitness advice.

Itsines became a certified personal trainer through the Australian Institute of Fitness in 2008 and was working one-on-one with clients at a local Adelaide gym when she decided to create a fitness program of her own.

"I realized that the methods I was being told to teach these women were not actually helping them achieve the outcomes they were seeking—toned arms and legs, flatter stomachs, strength," Itsines explains. "So I decided to do my own research and develop my very own training method that finally helped women get the results they had been working so hard for, for so long, without having to spend hours in the gym."

And so BBG was born, and an Instagram movement along with it. Alena Almquist-Heater, a 25-year-old Oregon native living in Germany, says the photos Itsines would post in the early days intrigued her because she was this "small, lean woman who was still able to perform all these crazy, body-weight exercises." Almquist-Heater became a Kayla devotee. "BBG literally kicks your ass."

BBG is a 12-week program consisting of 28-minute routines you do three times a week. It's a full-body workout that incorporates high-intensity interval training, plyometrics, and resistance training, utilizing moves like jump squats, walking lunges, knee-ups, burpees, mountain climbers, and push-ups. Itsines says BBG is meant to be accessible to people of all fitness levels and be done anywhere, whether it be a gym or a living room. While not required of the BBG program, Itsines also promotes a low-carb diet high in protein, fruit, vegetables, and whole grains on her blog.

Itsines initially started doing BBG with her training clients, posting photos of their impressively visible results on her Instagram. "I was getting so many requests from women all around the globe for advice and more information on how my clients and I trained," Itsines says. "I was sad I couldn't service them all to the extent that I wanted to. I wanted to bring something unique not only to girls locally, but internationally, so they could have the opportunity to feel fit, toned, and confident."

"I was totally inspired by the transformational photos."

This is what spurred her to offer a $69 instructional BBG e-book on her site. Itsines also encourages BBG users to take photos of their bodies during the program and share them online because "personal progress is one of the most important and successful forms of motivation." You'll find legions of Instagram accounts (Hannah Aloha BBG! Georgie's BBG! Sarah F. BBG! Little BBG Bear! Ready Set BBG! My Happy BBG Journey! BBG Argentinian!) created expressly for this purpose.

"I was totally inspired by the transformational photos," says Abbie Sterling, a BBG user who goes by @corporate_sneakers on Instagram. "I’ve always been a gym rat, working out four to five days a week, but I never saw results. The transformational photos of real people showed me that I could find a program that’ll actually give me results. When I first created my account, I made it private because I wasn’t sure how people I knew would react, but that’s changed and now I use it as a place to write and share ideas."

It's also a place to interact with BBG users around the world.

A photo posted by Kayla Itsines (@kayla_itsines) on May 5, 2015 at 1:33pm PDT

"Creating your own BBG Instagram is a way to connect with other like-minded people with similar goals, whether it’s to lose weight or get stronger," says Almquist-Heater. "As BBG users, we know the workout is hard—it pushes your limits—so you can relate when you see women posting sweaty selfies and red-faced photos of them lying on the floor. You can remember, ‘Oh yes, week eight’s arms were a total killer’ and encourage and support everyone on Instagram."

"It might sound funny, but I’ve made a lot of great friends through this digital community."

Becoming part of the BBG community is about more than just drinking the Kayla Kool-aid, echoes Kelly McKinnis, a 22-year-old college student living in Chicago: "I feel like when I talk about working out with my other friends, they get so tired of it. They think it’s all I do! They don’t get it because they don’t work out. But the BBG girls and I can really connect. It might sound funny, but I’ve made a lot of great friends through this digital community. We talk through Whatsapp or Instagram, which I never thought would happen, but we are all doing this together."

BBG users say they like the community because, unlike other fitspo corners of the internet, this one is intent on positivity. Take Erica, who joined the BBG movement just last week. She posted a "before" photo on her new BBG Instagram (@erica_fitnessbbg) with this caption: "I really can't believe I'm sharing this right now... I'm 19 and I'm at the heaviest I've been in my whole life." Within a day she was already seeing comments from strangers, like @jonesybbgjourney: "You can do this!!! I think you will love the guides :)" "You got this one day at a time," chimed in @christle_bbg.

Jess Anne of Kenosha, Wisconsin recently shared a photo of her progress, admitting that "the past couple years I have been in the double-digit sizes, so this is an awesome accomplishment for me!" Excited supporters commented with, "Looking great!!! Keep up the good work!" and "Congratulations! You look stunning."

"I've found it very difficult to converse with people on Instagram, but when I started with the BBG community, I found that the girls actually talk to you!" says Naomi ONeill an actress in Ireland. "Even if you're posting something about what you're eating, they are still going to listen to you. We actually have conversations."

This aspect is important to Itsines, who says her BBG girls "motivate me to work hard every single day and help me continue to strive towards my goals and dreams." Of course, in a community this large, there will undoubtedly be conflict. Earlier this year, Itsines sued Leanne Ratcliffe, a popular Australian fitness personality known as Freelee the Banana Girl, for defamation after Ratcliffe posted videos claiming Itsines's nutrition plan advocated starvation. But BBG devotees like ONeill say the emphasis on health, and safely achieving it, is part of the community's appeal.

"Kayla always has a very positive message," ONeill explains. "She’s never suggesting anyone be thin or skinny. She’s always pushing her followers to be fit, strong, and healthy, and that’s really important. Of course, the atmosphere can quickly change because we are women and women can be quite extreme when it comes to things like weight loss, but she never comes at it from that angle. She inspires girls to be girls."

While Itsines wouldn’t confirm BBG sales numbers, she has expanded her offerings to include BBG 2.0, a new 12-week program to be used after completing the original program, and a cookbook. She also sells equipment like foam rollers and fitness trackers, perhaps a response to her policy of not endorsing products or accepting money from advertisers.

"There are so many different fitness accounts on Instagram, but you're never really sure if they are being honest about what they actually wear or use," says Sterling. "You see all these accounts throwing product after product at you with random sponsorships. That’s why I think Kayla’s guide is so attractive to girls. She’s got so much personality and the bottom line is that she’s honest, which is so rare in the fitness community."

Itsines has also started to move her persona offline. In February, she started hosting free boot camps all around Australia and plans to tour Europe and the US later this year. Fans like Almquist-Heater say they plan to travel great distances to meet their fitness idol.

Then there are the BBG girls who have gone on to become fitness personalities themselves. Almquist-Heater now blogs at Healthy Living Dreams and has over 55,000 Instagram followers; she sees this as "paying it forward." Sterling, who has also become a fitness blogger and Instagrammer, adds that inspiring others motivates her to continue her own BBG journey.

Other users who've already reached their fitness goals still continue to live in the community, updating their Instagram accounts because they see BBG as an important part of their everyday lifestyle, not just a passing trend.

"Honestly, if I wasn’t on Instagram, I probably would have quit!" McKinnis laughs. "It’s really hard and there were times I didn’t want to work out, but I got myself to do it because posting the progress pictures was really cool and it was a way for me to stay involved in the Instagram community. The comments, the responses, the conversations that happen, it all reminds me that I’m the one who can change my body and its really empowering."