Ivar the Boneless isn't your average Viking. Sure, he's as ruthless, bloodthirsty, and untamed as the rest of his kin. But unlike his fellow Norsemen, Ivar will never lunge into a mob of angry Saxons or wield an axe in combat, and that's because he can't use his legs.

The character's paralysis presented a unique physical challenge for actor Alex Høgh Andersen, who plays Ivar on the wildly popular History Channel series Vikings. (And if you’ve already made the whole “Ivar skips legs day” joke in your head, don’t feel bad—Andersen beat you to the punch.) The 23-year-old actor would spend much of his time filming the show crawling on the ground, which would require not only a "special technique," but also an intense training program to bulletproof his lower back.

So how do you prepare to play a fierce warrior who's spent a lifetime dragging himself through the mud? You build an insanely ripped upper body.

At least three days a week (including a "no excuses" Saturday), Andersen sticks to a boxing-style workout of high-cardio drills and combos to build endurance: "It's just brilliant—it kills you every single time," he says. And while he admittedly doesn't go to the gym all that often, he does dedicate at least one day to upper-body (and only upper-body) weight training. ("I can't have my already-big thighs and butt all swollen because I'm squatting all the time," Andersen joked.)

Instead, he does a free-weights routine with "a lot of repetitions" that focuses on strengthening his chest, arms, and back. With some help from the Vikings team, Andersen selected a series of moves that not only helped him get "lean and sharp and strong" without looking bulky, but also applied to the work he was doing on-screen. Dumbbell pullovers are particularly important for his routine because "it's very close to the same motion that I do when I'm crawling," Andersen says.

Directions

This routine is an example of Andersen's upper-body workout. Perform this workout as straight sets. After you've completed the entire chest, arms, and back workout, move on to the core finisher circuit. Do three rounds, with each round progressively shorter than the last. Rest 30 seconds after each round.

Vikings Season 5 premieres on the History Channel November 29.