Sydney Sweeney’s 12-Week Boxing Transformation for ‘Christy’ Film

How Sydney Sweeney Gained 30 Pounds for Her Role in ‘Christy’

Beneath the polished streets of Beverly Hills, hidden behind valet stands and designer labels, lies an underground gym that almost no one knows about. No signs. No website. No social media.

But inside this “Batcave of fitness,” some of Hollywood’s biggest transformations have taken place — from Hilary Swank’s Million Dollar Baby build to Kumail Nanjiani’s Marvel physique.

And now, Sydney Sweeney’s powerful boxing body joins that elite list.

A Full-Circle Moment for Trainer Grant Roberts

Image source: Variety

“This place is paparazzi-proof,” trainer Grant Roberts says with a laugh. “You literally drive underground. The only way anyone finds me is through results.”

For Roberts, Sweeney’s training was deeply personal — a full-circle moment.

Twenty years after he helped Hilary Swank bulk up for Million Dollar Baby, Roberts found himself guiding another determined actress through the same mental and physical journey.

“The mindset, the athleticism — Sydney reminded me so much of Hilary,” he says.

Image source: Variety

The First Impression: Quiet, Focused, and Fearless

Like any seasoned trainer, Roberts approached the project with caution. “You never know what you’re walking into,” he admits. “Is the actor disciplined? Are they ready to commit?”

Image source: Variety

But the moment he met Sweeney over Zoom, those doubts faded.

“She was soft-spoken at first, just observing. But once we started training, everything changed,” Roberts recalls. “She’s one of the most genuine, hard-working people I’ve ever met. All in, from day one.”

From Euphoria Starlet to Christy Martin

Playing real-life boxing legend Christy Martin, known as “The Coal Miner’s Daughter,” wasn’t just about looking tough — it was about becoming a fighter.

Over 12 intense weeks, Sweeney — just 5'3" — gained over 30 pounds, transforming her frame into that of a professional athlete.

“Think about that courage,” Roberts says. “Sydney’s known for her beauty. Christy Martin? She’s a fighter — strong, fearless, and not worried about looking pretty while being punched in the face. Sydney embraced that completely.”

Related: How Votiv Secured Sydney Sweeneys Boxing Film Christy Rights

Around two-thirds of her weight gain was muscle. “She ended up putting on about 34 pounds total,” Roberts confirms.

Image source: Variety

Training in the Middle of Nowhere

Their camp wasn’t a Hollywood luxury setup. It was the opposite.

Sweeney and Roberts trained in rural Idaho, far away from paparazzi and distractions. They built their own mini-gym — complete with a boxing ring, heavy bags, and a small weight room overlooking a lake.

“It couldn’t have been more old-school,” Roberts laughs. “Just hard work, grit, and the sound of gloves hitting the bag. It was like something out of Rocky.”

Building Power Before the Ring

The first six weeks focused entirely on building muscle and strength — not just for looks, but for function.

“The goal was to make her move and hit like a real fighter,” Roberts explains. Once Sweeney’s physique was solid, professional boxing coach Matt Baiamonte stepped in to fine-tune her ring work.

“Sydney’s athleticism blew me away,” Roberts says. “She’s strong, fast, and incredibly disciplined.”

Food, Protein, and Perfect Timing

Roberts also handled all of Sweeney’s nutrition and recovery.

“She trained twice a day, so her meals had to support that,” he says. “We used 3D scans and body composition analysis to design her meal plan. Every shake, every bite was timed perfectly.”

Breakfasts started with protein shakes. Lunch and dinner were high in lean meats, carbs, and healthy fats. And yes — PB&Js made frequent appearances.

“She hit her protein goals first,” Roberts says. “After that, she could enjoy comfort foods to help gain healthy fat — to look believable as Christy.”

Before bed, Sweeney would drink a casein protein shake — a slow-digesting protein that helped her muscles recover overnight.

“It’s not just what you eat,” Roberts emphasizes. “It’s when you eat it. Every hour mattered.”

Image source: Variety

The Physical and Emotional Journey

By week five, Sweeney had already gained 20 pounds. Roberts remembers the moment she stepped on the scale.

“She looked at me with this mix of shock and pride,” he says, smiling. “Her back was developing, her shoulders were defined, and she’d added inches of muscle to her glutes. She was thrilled.”

The transformation wasn’t only physical. “Sydney didn’t just look like Christy Martin,” Roberts says softly. “She moved like her. She became her.”