The actor had long dreamed of making a Viking movie, and he was not going to let the opportunity to play the warrior prince Amleth go to waste. But acquiring the muscular physique required for nude volcano fights is no easy task, so he enlisted the efforts of celebrity trainer Magnus Lygdback. In a new interview with Variety, Lygdback details his efforts to transform Skarsgård from a Hollywood leading man to a Viking warrior. To build those massive traps, Skarsgård ate 3,700 calories a day, consuming clean protein every two to three hours to keep his metabolism up. Lygdback said that his meal plan for Skarsgård consisted of 20 meals every four days, with 17 of them consisting of a protein (often fish), a vegetable, and a complex carb or a fat. The other three were cheat meals where Skarsgård could indulge his cravings.

But the work did not end in the kitchen. Skarsgård’s gym routine was equally crucial, as they had to craft a workout that would create a historically accurate physique. His trainer began by looking at Amleth’s character traits. “This character, his spiritual animals were a bear and wolf. So that is exactly what we were trying to embody in terms of Alex’s build and movements,” Lygdback said. “The wolf is really agile, and then you have the size of the bear in this Viking. You can just get one look at him and get scared.” While anyone would be forgiven for thinking Skarsgård lived in the gym for a year before the shoot began, Lygdback revealed that his workouts were actually quite short, prioritizing efficiency over quantity. “You see it in interviews all the time where an actor says, ‘I trained for multiple hours a day.’ That’s not necessarily true,” Lygdback said. “They might have been moving around for four hours a day, let’s say, but the actual gym session? I never train my clients for more than an hour because what doesn’t happen in the first hour will not happen in the second hour at the gym. All you do after the first hour is just start to break down your body. So one hour a day, six days a week. While filming, five days a week.” “The Northman” is now playing in theaters.  Sign Up: Stay on top of the latest breaking film and TV news! Sign up for our Email Newsletters here.