Jamie Dornan uses his "body as a gym" and does workouts which combine yoga, gymnastics and bodybuilding.
The 'Fifty Shades of Grey' hunk worked out with Neil McTeggart from Belfast's IronFit to get in shape to play kinky businessman Christian Grey in the raunchy movie and used a mixture of yoga, gymnastics and body-building to hone his physique.
Neil told heat magazine: "Jamie was always a skinny kid, he's very lean.
"We do various workout programmes, like street work, which focus on body weight.
"Rather than using a lot of equipment, you use your body as your gym.
"We take the best moves out of things like yoga, gymnastics and bodybuilding.
"It's all about kettle bells, climbing ropes and doing gymnastic rings. Diet-wise, it's not restrictive.
"The great thing about body-weight training is you practise and can see yourself getting better and being able to hold yourself in a position for longer.
"It's about making you stronger and the body shows it."
Meanwhile, Jamie's co-star Dakota Johnson - who plays Anastasia Steele - favoured daily Pilates classes to get in shape for the movie.
Pilates teacher Mari Windsor said: "She does everything - the mat and reformer machine.
"She is very co-ordinated and graceful. She likes the leg springs, just like Miley Cyrus."