dakota johnson
Dakota Johnson said her Fifty Shades role had some 'painful moments'Getty/Jason Merritt

Whoever said filming a passionate on-screen romp was easy?

Hollywood star Dakota Johnson has revealed that she was left with an agonising neck injury while filming a sex scene for the upcoming Fifty Shades of Grey movie.

The actress, who takes on the role of submissive Anastasia Steele in the S&M flick, told Glamour magazine that she suffered whiplash when her co-star Jamie Dornan threw her onto a bed multiple times.

In the movie, the stars play bondage-obsessed playboy billionaire Christian Grey and his compliant lover.

Although they admit that acting out rigorus S&M scenes put their professional skills to the ultimate test, Johnson said that Dornan was the perfect gentleman when the cameras stopped rolling.

"Jamie would be the first one to throw a blanket over me. And he did a lot of studying, just to make sure that I was as safe as possible. But there were some painful moments. I got whiplash once, from him throwing me on to the bed. But that was only because we did it over and over and over again."

Dornan added: "I felt very protective and aware that it probably wasn't easy for her to be put in those situations."

Meanwhile, it has been revealed that the film, which is based on EL James' bestselling erotic novel, will have more than 20 minutes of sex scenes during its 100-minute running time.

According to Mr Skin, a website that compiles data on the duration of sex scenes in movies, the quantity surpasses the total duration in 100 of the raunchiest mainstream films released in 2014.

Fifty Shades, which is set for worldwide release on Valentine's Day (14 February), also stars Rita Ora, Marcia Gay Harden, Jennifer Ehle, Max Martini, Luke Grimes and Eloise Mumford.

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A still from the second trailer of Fifty Shades of GreyYouTube