Brie Larson Says "Captain Marvel" Inspired Her to Train Out of "Pure Fear of Failure"

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In recent years, Brie Larson has become a fitness inspiration in her own right — but it wasn't until after she was cast in "Captain Marvel" that she became serious about training. During an appearance on "Jimmy Kimmel Live" Wednesday evening, the actor spoke about her workout journey, sharing that she first started working out when she was cast as Carol Danvers "out of pure fear of failure."

"I thought I was supposed to do my own stunts," she said. "They casted me, and I was like, 'Uh, they low-key don't understand that I'm an introvert with asthma. They made a mistake. I gotta figure this out real quick.'"

"It really transformed my life, and 'Captain Marvel' changed me as a person."

But once she started working with her personal trainer, Jason Walsh, she learned, "I was actually much stronger than I realized." She discovered her allergies were causing her asthma, so she started taking allergy medicine and began to lift heavy weights. "It really transformed my life, and 'Captain Marvel' changed me as a person."

Though her "Captain Marvel" role was what initially inspired her to build her strength, Larson seems to have fully embraced a love of fitness. From a 244-pound "tank" push and kettlebell windmills to an upside-down hanging crunch and full-on pole dancing, she's displayed her impressive, powerful moves on Instagram and YouTube alike. She even scaled Grand Teton mountain in Wyoming — the highest point in Grand Teton National Park at almost 14,000 feet — a difficult feat she joked was probably in violation of her contract with Marvel. "It was absolutely remarkable," she said of the experience on Kimmel. "It changed my life, but every step of the way, I was like, 'Yeah, I'm probably gonna die.'"

Above, watch Larson and Kimmel chat about her fitness journey, as well as Larson's new Disney+ docuseries "Growing Up."