These two best friends started a fitness revolution for women on Instagram

Tone It UpInstagramKarena and Katrina taking a selfie.

Two women have inspired hundreds of thousands of women to get off their butts and start living healthy lives by working out and eating nutritious food.

And it’s all thanks to Instagram.

The best friends have started a #ToneItUp community, where they teach women how to work out and what to eat.

They also make it really fun — it’s hard to not want to become friends with them when you watch their YouTube videos and Instagram uploads.

Now they have books, a show on Bravo, and have made countless appearances on television and in magazines, all while travelling all over the world to meet their fans and supporters.

Meet Karena and Katrina and the #ToneItUp community.

Meet Karena and Katrina, the founders of #ToneItUp, one of the most popular weight loss programs for women.

This is Karena.

And this is Katrina.

They have graced the pages of magazines, and appeared on various talk shows (they even have a show on Bravo!) but most of their fans are on Instagram.

They have created a #ToneItUp community, where women all over the world track their success on the program and post it to the social platform. The girls have 420k followers.

But they weren't always in such great shape. They weren't always best friends, either.

Katrina is a weight loss success story, she says, and moved to California to be a trainer. That was where she met Karena, and tried to get her to be her friend.

'It took finding me at Trader Joes and forcing me to take one of your classes!' Karena has told Katrina, remembering the beginning of their friendship. Now they're inseparable.

Within a year of becoming friends they opened their first fitness studio where they taught beach boot-camps in a 400sq foot space.

But as they built their following on Instagram, they were able to inspire women from all over the globe to #ToneItUp.

They have books on their weight loss and nutrition program. You can also become a lifetime member and have access to workouts and recipes.

They make tons of YouTube videos.

Karena was even the maid of honour in Katrina's wedding.

It's hard not to get inspired! Karena and Katrina are in great shape.

And they're fun. They recently did a remake of Beyonce's '7/11' video and encouraged their #ToneItUp community to do the same. They got hundreds of submissions.

But what's most inspiring is seeing what the fans have to say. This woman says she lost 30lbs doing #ToneItUp. 'I am so grateful for discovering #TIU! I joined the #TIUteam in early 2013 & became a member that summer! I'm so happy to be on this journey love spreading #TIUlove!'

They have inspired women to have meetups all over the country.

Thousands follow their mantras and words of wisdom.

And follow their nutrition advice.

'We wanted Tone It Up to be a place that all women can visit and relate to,' they have said.

You can learn more about Tone It Up, and the girls' super successful Instagram accounts by clicking the links below.

Now meet another Instagram fitness sensation...

Business Insider Emails & Alerts

Site highlights each day to your inbox.

Follow Business Insider Australia on Facebook, Twitter, LinkedIn, and Instagram.