A 25-year-old fitness entrepreneur from Adelaide is putting her own twist on group classes that are being attended by thousands of people at a time.

Kayla Itsines, who is on the BRW Young Rich List of wealthiest Australians and shares a net worth of $A46 million with partner Tobi Pearce, has been inspiring women across the world to get fit for years.

But it is her ‘bootcamps’ that are creating particular interest, with more than 2200 members of her ‘Bikini Body Guide’ community turning out at Melbourne’s Olympic Park on Thursday evening.

In addition to a traditional intense Itsines workout, the personal trainer’s followers broke five Guinness World Records for simultaneous physical activity.

“Working as a team to not just achieve our fitness goals, but also to break these records today, really proves that we are the largest and most influential fitness community in the world,” Itsines said afterwards.

With a Guinness representative on standby, the records were quickly recognised by the organisation.

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While the Melbourne crowd was no doubt swelled by the world record attempts, Itsines has a track record of getting huge numbers to attend her bootcamp sessions across Australia and the world.

As part of her ‘2016 Sweat Tour’, she held bootcamps in London, New York City and Los Angeles, all of which attracted thousands of fans.

Journalist Katie Maguire of WellGood wrote of the experience attending Itsines’ New York session and said: “When I arrived … you could tell something huge was going on … girls were surrounding the doors from all directions.

“[Once inside and after a long wait] running down the staircase to the stage like Kobe Bryant [famous basketballer] entering the Staples Center, Itsines made her way front and centre – and waited for everyone to finish screaming. It took two full minutes.

Kayla’s classes are very popular. Photo: Instagram

“Itsines was a true boot camp professional. It was a tough workout by any standard and, although I wasn’t even a fan before, I was genuinely impressed by the boot camp.”

And it’s not just Kayla’s idea, with large fitness classes particularly popular in other nations, including Brazil.

Pedro Hallal has been behind the implementation and running of wide-scale outdoor classes across the South American nation.

In Brazil, trained health professionals give free workouts and advice to locals for no cost every morning and evening, with the government funding the program to the tune of approximately one billion US dollars.

The psychology behind group exercise

So, why are these massive classes becoming so popular?

Dr David Cubans, an expert on exercise from the University of Newcastle, told The New Daily: “I think these types of activities are so popular for strong social reasons.

“People love being active together and this environment [that Kayla provides] seems fun, with music playing. It almost has a kind of festival feel to it.

“There’s a growing body of evidence that states social support makes it much easier for someone to maintain a fitness program.”

Exercising in a group keeps people motivated. Photo: Getty

Dr Cubans also said that less individual attention on a participant was particularly appealing.

“With so many people involved, it can take the focus off the individual, which is an environment that some find threatening,” he said.

“Lots of people, particularly women and adolescent girls, can feel uncomfortable exercising on their own when people are watching.”

He predicted the trend would become more and more popular, adding: “This is fun, accessible and comes with the mental and physical benefits of being outside … I don’t see why it wouldn’t continue to grow.”