'Superhero summer camp': How 'Thor' stars Natalie Portman, Tessa Thompson bulked up for their roles

Natalie Portman makes a thunderous return to the "Thor" franchise in "Love and Thunder."

Astrophysicist Jane Foster, absent from the series' last installment, 2017's "Thor: Ragnarok," takes her own hammer swing at superhero, portraying the Mighty Thor. She helps Thor (Chris Hemsworth) in his battle with Gorr the God Butcher (Christian Bale), who's vowed to kill all the gods.

The role required intense preparation, from workouts and diet to lifestyle changes, Portman learned.

She says director/screenwriter Taika Waititi's vision drew her to the film (in theaters Friday). "When Taika came to me and had this idea of bringing Jane back, but in a completely new way, I was obviously excited," she says.

Marvel's first solo female-led superhero movie arrived in 2019 with "Captain Marvel," starring Brie Larson. Last year's "Black Widow," centered on Natasha Romanoff (Scarlett Johansson), followed, along with Disney+ series "WandaVision," "Hawkeye," "Ms. Marvel" and "She-Hulk: Attorney at Law" (debuting in August).

Portman, 41, liked "the hilarity and awesomeness" of "Ragnarok," and jumped at the chance to work with her "Annihilation" co-star Tessa Thompson, whose Valkyrie is now king of Asgard. Thompson says her character is "really happy to have found a new sister, and certainly (a) new adventure when the Mighty Thor comes her way."

Portman says Valkyrie "is also very encouraging with (Jane) with regard to all her doubts and having to learn how to be a superhero on the fly."

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Similarly, Portman leaned on Thompson in real life. Portman thought for her transformation she would just "work out a lot and like lift weights.” But Thompson and Hemsworth offered more guidance. "They were like, ‘Oh no, this is a whole lifestyle commitment where you have to be eating and drinking all of this protein.'" Portman says she steamed in saunas and took ice baths.

If social reaction means anything, her hard work paid off. Her toned arms rocked the internet, with Twitter users "drooling over" her muscles and pondering the meaning of the film's title: "'Love and Thunder': Is that just the movie title or is it what Natalie Portman's Thor calls her left and right arms?"

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Thompson says she enjoys bulking up for Valkyrie as the rare appearance of a muscular woman is memorable.

"It's also why the internet had such a strong reaction to seeing Natalie's arms," Thompson says. "There's something very visceral about seeing a woman just look really, really strong and muscular, and how it upends those ideas around gender and gender expectations."

For the 2010 ballet drama "Black Swan," which won Portman an Oscar, preparing meant "trying to get as small as possible," she says. "I was strong, but I was starving myself. To be tasked with eating as much as possible and feeding my body what it needed and feeding it what was gonna repair the muscle and grow it, that was a pretty wonderful challenge."

Portman found humor in the social reaction to her beefed-up arms. "It was definitely funny," she says, crediting trainer Naomi Pendergast for her physique. "She was working a lot on really inner deep muscles, too," which remedied Portman's aches. "It was really such a gift to get to have that at that time in my life, turning 40," the actress says. "I (felt) like, 'Oh, my God. I'm old.' Now I actually feel like the best in my body that I've ever felt and the most strong and the most balanced and least in pain."

Today, Portman's arms don't exactly match the ripped ones in the movie.

"It's also a lot of movie magic that went into that," she says with a laugh. "So it's not like even then, that I looked like I do in the movie. I also stopped the rigorous daily stuff, but I am still benefiting from all of that body balancing that Naomi did with me, which I should probably do more of."

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Thompson admits "I am definitely not always in shape," especially during the pandemic, when "Love and Thunder" was filmed. "Like very many people during that time, I was eating my feelings and cooking a lot to ward off anxiety. And baking and not a lot of exercise. I really envy people that love to exercise; I'm not one of those people."

Thompson prepared with an "intense diet," lifting weights and doing two hours of cardio a day that resulted in a new love for audiobooks. Getting stronger is "mostly really fun" but also "kind of torturous. But at least we all can complain about it (together). It feels like superhero summer camp."

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Contributing: Brian Truitt

This article originally appeared on USA TODAY: 'Thor: Love and Thunder': Natalie Portman on building mighty physique