"The eighteen hour days start showing up," Zellweger admitted. "You get to work in the morning and you go, 'Oh my god.' And when you do eighteen hour days for three months, they really, really show up."
"[But] it's fun. You want to evolve. You want to keep going. I don't want to keep doing the same thing and keep telling the same stories," she qualified. "I think human experience, it gives you character and it makes the characters that you are prepared to play much more interesting.
Zellweger was 31 when the first Bridget Jones movie, Bridget Jones's Diary, opened in theaters in 2001. She returned in the sequel Bridget Jones: The Edge of Reason (2004), and is reprising the character now 12 years later.
"It's her humanity. She's imperfect and she makes it okay for the rest of us to be imperfect," Zellweger said of Bridget's lasting appeal. "We love being privy to her inner dialogue, her anxieties and her self-deprecating humor."
"We all know what it's like to put yourself in the middle of an escalating disaster -- realizing that you can't get out of it but yet doing your best to proceed anyway," she elaborated. "I mean, who doesn't relate to that?"
Zellweger had discussed the "social pressure to look and age a certain way" in an op-ed for The Huffington Post this month. She faced plastic surgery rumors in 2014 after fans deemed her nearly unrecognizable at a red carpet event.
"Not that it's anyone's business, but I did not make a decision to alter my face and have surgery on my eyes," the star asserted. "It's no secret a woman's worth has historically been measured by her appearance."