An American publishing powerhouse has named Adelaide's Kayla Itsines as the world's most influential fitness identity.

In its inaugural list of industry influencers, Forbes described the 25-year-old - who has a whopping 11.6 million Facebook followers and 6.7 million Instagram followers - as "the internet's undisputed fitness queen".

"And a multi-millionaire to boot," it said.

It is the latest in a long line of accomplishments for Ms Itsines, who, together with boyfriend and business partner Tobi Pearce, were South Australia's only inclusion in the 2016 BRW Young Rich list with a combined $46 million fortune, reports News.com.au.

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Their fortune has been amassed via a Bikini Body empire, which includes fitness classes being held across the world - more often that not in packed stadiums - book sales, and smartphone app Sweat With Kayla - last year's most-downloaded fitness app globally, according to analytics firm App Annie.

Those downloads generated $US17 million of revenue in 2016, according to Forbes.

"The cult of Itsines grew entirely organically," Forbes told its audience in an overnight article.

"Left in charge of the Adelaide gym where she worked by an absent manager in the late noughties, the then-teen began developing a program to target what she saw as problem areas for women: abs, arms, and thighs.

Forbes described the 25-year-old as
Forbes described the 25-year-old as "the internet's undisputed fitness queen". Photo / Facebook: Kayla Itsines

"Itsines' online presence remains relatable despite her fame and considerable fortune, much to the relief of her many millions of fans.

"She's partial to the heart-eyes emoji, and in between fitness tips and photos of fruit plates or beach vistas, she posts motivational quotes."

In an interview with SA Weekend late last year, Ms Itsines described users of her app as "family ... like a big group of sisters".

"It's a community of women who just want to support each other and see each other do well," she said.

Forbes ranked US online identity Jen Selter second behind Ms Itsines, describing her as someone "who went from the front desk at her gym to the leader of a booty-boosting workout movement", and Australian Emily Skye in third position.

Eight out of top 10 were women - Joe Wicks and Simeon Panda ranked fifth and seventh respectively.