Freed is the third and final part of the Fifty Shades of Grey trilogy, and comes out at the end of this week.
Renowned for its erotic content, it’s certainly been a taxing process for Johnson, playing the lead role of Ana Steele.
“The subject matter is obviously intense,” she told ET. “To have that coupled with the commercial [scale] of the film was difficult to handle sometimes, to get through it.
“These [sex] scenes are physically and emotionally quite vulnerable, and sharing them with the whole world.”
After being reminded of co-star Jamie Dornan’s habit of doing push-ups and preening himself before a scene in which he’d have to take his clothes off, Johnson said she needed “serious psychological preparations”.
“There is a lot more of my body that is shown than Jamie’s, and he’s the one doing push-ups!
“It’s not easy to do. I really had to get ready for it each time and know exactly what we were going to do, how we were going to accomplish the scenes, the more intimate ones.
“They never got easier. Jamie and I are so comfortable with each-other so we felt safe and protected but it’s still an environment that’s scary.”
Dornan is never seen fully nude in any of the movies, and denied a rumour claiming he turned down an extra $1 million to show everything.
“I just thought, ‘We don’t need to be flashing the rest if it’s not essential to the story’. We’re not making porn as much as people think we are,” he told Elle.
Fifty Shades Freed is out on Friday.