Go ahead: Deny knowing anything about the 50 Shades of Grey series. But we'll be you know damn well the, ahem, thrust of its storyline is sex, some vanilla sex, and loads of kinky sex. You probably also recognize the two stars acting out those plotlines in the flesh, too, even if you haven't read the books or seen the flick: Dakota Johnson and Jamie Dornan.

Now, say you have seen the first installment of the trilogy, and you just happened to have seen the trailers for 50 Shades Darker (in theaters Feb. 10). You might have noticed Jamie Dornan (he plays Christian Grey) has seriously amped up his fitness regimen.

He was lean and in good shape for the first film—the guy was naked, or mostly naked, in majority of the movie—but he's seriously hit the gym for Darker, his trainer Ramona Braganza told the New York Post. Makes sense: Dornan does shirtless pullups, makes light work of a gymnastics maneuver, and basically shoulder-presses Johnson's character in a slick and steamy shower scene.

How'd he get there? “I focused on an athletic muscular frame for him—not too bulky…but strong in appearance," Braganza said. The brunt of Dornan's workouts—30-minute sessions, done twice a week—centered around lower-body work, since leg workouts stimulate the greatest release of testosterone. Aside from lower-body work, weightlifting and high-intensity exercise torch the most calories and get you faster results.

Specifically, Braganza challenged Dornan with two key exercises:

1. Bodyweight squats (Expert tip: Squeeze your glutes at the top of the movement to trigger the most muscle stimulation.)
2. Weighted squats (Expert tip: Use dumbbells and kettlebells to perform goblet squats. Check out more squat variations here.)

Throughout the rest of the week, Dornan worked his arms, back, and other body parts on his own to balance out his leg work with Braganza.

Want some more next-level advice for honing an irresistible, muscle-bound body?

We'll leave the rest up to you.