Amanda Seyfried spent weeks 'dancing through grief' to prepare for The Testament of Ann Lee

Amanda Seyfried spent weeks "perpetually dancing through grief" in rehearsals for The Testament of Ann Lee.

In the period drama, the Mean Girls actress plays 18th-century religious leader Anne Lee, who lost four children and channelled her devastating grief into the creation of the Shakers religious movement.

The movie contains offbeat musical numbers that depict how the Shakers used song and movement to express their emotional state.

To prepare for the shoot, Seyfried spent more than a month at a dance studio in upstate New York with choreographer Celia Rowlson-Hall to learn Lee's unusual dances.

"Celia and I both live upstate, so we met at this little, beautiful acting class/dance studio and just spent hours and hours and hours - weeks, probably over a month and a half - of just perpetual dancing through grief," she told Variety.

"Here, we're hearing this music - this incredibly melodic, very abstract-at-times music that was kind of designed through the Shaker hymns. You feel like it lends itself to a certain type of movement as well, and more primal movement, for sure."

Although she has learned dance moves before for the Mamma Mia! films, The Housemaid star admitted that the choreography was one of the most "challenging" aspects of the film because she doesn't "move naturally in these ways at all".

Seyfried noted that she had to keep going over and over the movements to make sure they became muscle memory.

"To get muscle memory, you have to just repeat, repeat, repeat, and that's sometimes very frustrating, very boring at times," she added.

The Testament of Ann Lee, which also stars Lewis Pullman, Thomasin McKenzie and Stacy Martin, will be released in U.K. cinemas on 27 February.