Amanda Seyfried "couldn't breathe sometimes" while rehearsing for 'The Testament of Ann Lee'

"I couldn't breathe sometimes." Amanda Seyfried opens up in a new featurette about the "challenge" of making Searchlight Pictures' new movie, "The Testament of Ann Lee."

"We just worked hours and hours and hours for weeks. I couldn't breathe sometimes," Seyfried said. "To be able to sing live, dance, perform. It was hard, but I love that challenge."

"The Testament of Ann Lee" director Mona Fastvold revealed the Emmy-winning actress worked on the choreography "almost a year in advance of shooting." "I knew that I needed someone who was just willing to just completely give themselves to this performance."

The film's composer Daniel Blumberg shared, "To see Amanda make such an ambitious project on this scale, it's impressive and inspiring."

"The Testament of Ann Lee" follows the true story of Ann Lee (portrayed by Seyfried), the founding leader of the Shaker Movement, a religious sect from the 18th century. The movie shows the agony and ecstasy of her quest to find utopia, featuring over 100 minutes of music and dance movements.

Watch "The Testament of Ann Lee" in select theaters this Christmas.

The Walt Disney Company is the parent company of Searchlight Pictures and this ABC station.