Scarlett Johansson Says She 'Had Never Stepped Foot in a Gym' Until Getting Cast as Black Widow

Amy Sussman/Getty Images Scarlett Johansson

Becoming a superhero when she joined the Marvel Cinematic Universe in 2010 was a heroic effort for Scarlett Johansson.

The 37-year-old actress, who was in her early twenties at the time, had to quickly build muscle and get in superhero shape, a major change for someone who wasn't used to working out.

"That was a humongous moment for me because I was, I don't know, 23 or 24 when I was cast in Iron Man 2. I had never stepped foot in a gym, and I had five weeks to prepare myself for these huge stunt sequences," Johansson told Vanity Fair in a new interview.

Cast as Natasha Romanoff, aka Black Widow, Johansson had to do a significant amount of stunt work.

"I was doing these huge choreographed sequences and I had no previous experience with any of that stuff. It was just a massive lifestyle change immediately upon getting cast," she said.

Marvel/Paramount/Kobal/Shutterstock Scarlett Johansson as Black Widow

The first step for Johansson was joining a gym, which was intimidating for a fitness newbie in body-obsessed Los Angeles — but she ultimately found a good trainer.

"I was living in L.A. at the time, and I went to this massive, huge, muscle meathead gym. I didn't know how to use any of the equipment. I mean, I was so intimidated," she said. "Luckily I had a really great trainer, this guy, Bobby Strom, who was training my husband at the time, Ryan [Reynolds]. And he took me under his wing and was so positive, and really made me understand what functional training was. And I could never go back the other way."

Now, Johansson said, exercise is a big part of her life.

"Fitness is such an important part of my mental wellness," she said.

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Johansson, who welcomed son Cosmo with husband Colin Jost in August, also talked about dealing with public scrutiny of her body during pregnancy. The added attention is part of why she kept that pregnancy, along with her pregnancy with 7-year-old daughter Rose Dorothy, whom she shares with ex-husband Romain Dauriac, under wraps.

"I've been so protective of both pregnancies, not wanting to feel scrutinized in the public eye," she said. "I wanted to be able to have my own feelings about my changing body without other people also telling me how they saw me, whether it was positive or negative."