Reese Witherspoon has had many emotionally challenging roles, but her turn as the protagonist in Wild, out Dec. 5, might be the most physically taxing of her career. "It's been so physically challenging," Witherspoon told ET. "Whether it's climbing on the side of a mountain, or crossing a freezing cold river and then falling into it, or hiking through the snow and she falls in waist deep, because that's what really happened." NEWS: Reese Witherspoon and Oprah Celebrate 'Wild'\n \nWild, an adaptation of Cheryl Strayed's best-selling 2012 memoir, is the story of a woman who has lost everything. After the death of her mother and the dissolution of her marriage, she decides to turn her life around by hiking the the 1,100 mile Pacific Crest Trail, despite having no prior experience. It\u2019s a harrowing tale that translated into a brutal production, but for Witherspoon, Wild is a true passion project. She optioned the rights herself to get the film made after reading Strayed's book. "I was really seeing a deficit in the marketplace of strong female roles and women as the lead in films," Witherspoon told ET. "I realized if I wasn't going to start creating these opportunities for myself and other women, nobody was going to do it." VIDEO: Reese Witherspoon Portrays Heroin User In Gripping 'Wild' Trailer Despite the battle to get the film made and the physically taxing production, the actress and producer feels it will all be worth it if audiences are inspired by the movie like she was inspired by Strayed. "I read her book and I was transformed," Witherspoon said. "I hope the film transforms people and heals people in the same way."