The 34-year-old Northern Irish actor explained that the film director wanted a scene of his character working out, but wanted something different. Dornan said that he had this "one party trick" he can do on a pommel horse -- which Conan asked him to recreate on his desk.
"Just before I do this, if I break my face or anything, you will pay for the whole thing," he says to Conan, to which the host replies, "I myself, I will not personally pay for it, that's something that Andy's on the hook for."
He then proceeds to climb on the end of the desk to do the pose.
"I am honestly not exaggerating, I just pulled my pec," Dornan says after, grimacing.
Dornan was recently on Ellen promoting 50 Shades Darker and did a skit spoofing the erotic film with the host.
The Fifty Shades movies are based on the book trilogy by E.L. James. Fifty Shades Darker, which opens Feb. 10, was preceded by Fifty Shades of Grey, and will be followed by Fifty Shades Freed in 2018.