The 'hardcore' exercise class responsible for Sydney Sweeney's toned body...and why some say it's the toughest workout they've ever done

Actress Sydney Sweeney just dropped the secret to how she maintains her world famous body. 

She's taking part in a hardcore Pilates-inspired workout that's sweeping the nation. 

'I like this place called SolidCore. It’s a full-body high-intensity workout but on a reformer, and it’s been killing my ass. I love it' the 'Euphoria' actress told The Wall Street Journal. 

SolidCore was founded in 2013 in Washington D.C. by Anne Mahlum, former non-profit worker turned entrepreneur. She created it to be 'pilates core workouts redefined'.

Sweeney burst into popular culture with her role as Cassie Howard in HBO's 'Euphoria'

As of December 2023, they've expanded to over a hundred studios across America- from California to North Dakota to New York.

But it's not cheap: individual classes cost $43 and a six-month unlimited membership costs $367.94 per month. 

The class takes place on a machine that Solidcore calls a 'swetlana', which is essentially a larger version of a Pilates reformer. This longer length makes certain moves more challenging. 

You can adjust the strength and tension of coils attached to different parts of the machine to create more or less resistance as you move through different exercises in the class. Using these sorts of machines for resistance exercises are said to improve posture, balance and add extra tension to challenge muscles.

But there are key differences between Solidcore and reformer Pilates. 

Solidcore has more of a focus on muscle and endurance building, while Pilates brings encourages deep, slow breaths and more gentle training.

The pace is also much faster - similar to that of a spin class. 

Newcomers are expected to come to class early for an orientation to this machine, which to novices, might look like a torture device.

Once the 50-minute class starts, the lights are dimmed and music begins blaring, not dissimilar to cult-following spin classes like SoulCycle or Orangetheory.

As the music plays, the instructor shouts directions over a headset attached to the speaker system, talking participants through a total of 25 different exercises- from planks, to lunges, squats and bicep curls. 

Solidcore classes take place on a machine called a 'sweatlana', which helps increase the challenge for your muscles

The instructors direct participants to hold each pose for extended periods of time while making small, slow contractions or stretches, pushing towards 'muscle failure'. 

This, the Solidcore team said, will help you build lean muscle endurance by stimulating slow-twitch muscle fibers.  

'Slow-twitch muscle fibers are fatigue-resistant, and used for activities that require endurance. By progressively increasing resistance over time on our Pilates-inspired reformer, muscles gradually become stronger,' they explain on their website. 

In normal people speak, the class is designed to make you shake. 

Scientific literature does agree that in order to build slow-twitch muscles, people should perform slow, endurance exercises to the point of muscle failure. For example, marathon runners tend to have very strong slow-twitch muscles. 

Sweeney is far from the first person to have been 'killed' by this intense workout.  

'Every step, I was shaking. Needless to say, SolidCore ain't no regular pilates,' TikTok user reallyemely shared in a video sharing her first experience. 

'This is the hardest freaking class I've ever taken in my life. I've never been so humbled,' user Lavishlana said in another video. 

In response, the official SolidCore account commented, 'the shakes mean it's working!'.