Lily James Didn't Speak for a Week Before Filming 'Mamma Mia 2' So She Wouldn't Lose Her Voice

Lily James went to extreme measures to make sure her voice was in tip-top shape before filming for Mamma Mia! Here We Go Again began.

In the sequel to the beloved 2008 film, which centers around the music of ABBA, James portrays a young version of Donna (played by Meryl Streep), and sings along with her group The Dynamos.

James revealed to PEOPLE, just days before the film hits theaters on Friday, that she’s “struggled” with her voice a lot since leaving drama school. “I lose my voice a lot,” she said. “I have issues — it’s really scary and heartbreaking.”

To prepare for her singing parts in the film, the actress said she “didn’t speak for a week before we recorded.” “I went on steroids and didn’t talk,” she added.

“I watched Mamma Mia over and over again to channel the essence of what makes Donna so unique and brilliant and fearless and courageous,” James continued.

The actress, 29, also said that when watching the film, she tried to “mimic a certain amount of [Streep’s] physicality,” including her hand gestures and “her gravity.”

James also prepared for her role by watching many of Streep’s other films, especially “stuff where she’s more comedic.”

“Postcards from the Edge was useful because she sang,” James explained, adding that Streep’s character was a bit “manic in that film and there is a bit of madness to Donna, a ballsyness and scattiness.”

Praising Streep, James added: “Like all great actors, Meryl is able to be a great comedian and break people’s hearts.”

As an actress who has taken on a broad range of roles herself, James remarked, “I think if you’ve want to keep it interesting then you’ve got to keep it varied as repetition is the death of creativity.”

James also had great things to say about Mamma Mia! Here We Go Again‘s message, describing the movie as “a celebration of women, motherhood and sisterhood.”

“It’s set in the seventies but it may as well be now,” she continued. “There’s a real sense of the freedom of her choice and of her sexual choice and embracing all of what it is to be young, free and single and to live on her own terms and to have the baby on her own on an island in the middle of nowhere.”

Mamma Mia! Here We Go Again takes place back on the Greek island of Kalokairi five years later with Amanda Seyfried’s character running her mother Donna’s inn — with the help of her mom’s former bandmates, Tanya and Rosie (Christine Baranski and Julie Walters).

The entire original cast reunited for the film, including Colin Firth and Pierce Brosnan, with James and Cher as the newcomers. Cher plays Donna’s mother, Ruby Sheridan.

Mamma Mia! Here We Go Again in theaters Friday.