Whether it’s Brad Pitt’s shredded frame in Fight Club or Henry Cavill getting superhero-jacked for Man of Steel and Batman v Superman, fans are obsessed with celebrity fitness transformations—and Justin Hartley is no exception. For years, Hartley has made a name for himself in roles that showcase his physique. In This Is Us, he plays Kevin Pearson, the athletic, spotlight-chasing “eldest” Pearson triplet known for his ripped build and football roots. In Netflix’s Senior Year, he takes on the role of Blaine Balboa, the confident, popularity-driven high schooler who’s more than a little hung up on his appearance.
But Hartley’s latest role is a major pivot. In Tracker, an American action-drama series, he stars as Colter Shaw, a rugged, lone-wolf survivalist who uses instincts and grit to find missing persons and claim rewards. This time, Hartley’s not weight training just to look good—he’s mostly using cardio to push his limits to keep up with a role that demands strength, stamina, and serious physicality.
"Have you ever taken a jog or a run through the woods [at] full speed?" he says. "Your footing is never the same….You can run the same path 30 times, and every time will be different. Trail running is a bizarre thing…but there's that strengthening of all of those tiny little muscles around your knees and your ankles and your hips. It's a different animal than just cosmetic working out to look good. There's a function to it."
While lifting heavy isn't a huge part of Hartley's routine for this role, he still wants to be in what he calls "wiry" shape. The kind of guy that could "probably crush your skull with their hands, and they're really strong, but they're not bodybuilder type guys."
He remembers when he first signed on to Tracker, both he and executive producer Ken Olin envisioned his character as more of a lean, agile rock climber, similar to how he was portrayed in the book The Never Game. Given that the role required a lot of movement—running through the woods, scaling rock faces—Hartley didn’t want a bulky, bodybuilder physique.
But as the show developed, so did his character. Colter Shaw became less of a climber and more of a survivalist who regularly faces dangerous situations that often turn physical.
"As the show moved on and evolved and changed a bit, the character kind of changed, and it was like, 'Oh, maybe not such a rock climber,'" he says. "So I got a little bit bigger, not too much. I put like five pounds on, maybe seven pounds on or something like that, of muscle, and just changed my workouts [to include] a little bit heavier weights every now and then."
