Actor Alan Ritchson was a scrawny high school junior in Niceville, FL, back in 1999. Like many of us who were desperate to add muscle to our skinny frames, he relied on bodyweight moves such as pushups, pullups, situps, and dips. He’d do “ladder circuits,” performing one rep of each, then two of each, all the way up to 25 of each. And then he’d reverse course and make his way back down to one of each. “I was doing whatever I could to fill out and catch up to everybody else,” says Ritchson. Mission accomplished.

These days, the lean and muscular Ritchson—who appeared in The Hunger Games: Catching Fire, Teenage Mutant Ninja Turtles, Blue Mountain State, and about 30 other TV shows and movies—resembles a Ken doll who just finished Navy SEAL training. In fact, he actually faces the opposite problem of his youth: the danger of getting too big. “My genetics lend themselves to size, so if I wanted to get enormous, I could,” he says. “If I start working out with weights or bench pressing at the gym, I would look like an ogre.”

Which is why Ritchson’s current workouts haven’t really changed much since his high school days. His training consists of long runs (up to 13 miles a day), plus sprints, pushups, dips, pullups, situps, and burpees. (He belongs to a gym, but he chose it because it had really good pullup bars for muscle-ups.) “I get outside as much as I can,” says Ritchson. “I live in the hills in L.A., so I [run] on Mulholland Drive or the trails in the Santa Monica mountains. It adds something to the runs.”

Of course, that’s when he’s in Los Angeles. For his latest project, Blood Drive—which is currently airing on Syfy—Ritchson was shooting for several months in Cape Town, South Africa. On the show, Ritchson plays a former cop thrown into an underground death race across America in a dystopian future.

The kicker: All the cars run on blood (hence the title). Blood Drive is not for everyone, warns Ritchson. “I genuinely don’t think there’s anything else like this show,” he says. “Every episode touches on a different genre of grindhouse. There’s the cool, Western, Tarantino-style grindhouse thing one episode, and then there’s more Night of the Living Dead one episode. It’s a crazy show. If you’re watching Once Upon a Time on ABC, this is not for you.”

What’s next for Ritchson? Like many actors, he would really like to direct. He’s started making short films, and says his heart is more behind the camera. Still, he realizes what’s paying the bills, and will continue to cultivate a body type that can help him portray a wide array of characters. He says he’s aiming for a swimmer’s physique and achieves this with, in addition to his intense bodyweight workouts, an 80/20 diet that includes no dairy, no refined sugar, not much red meat, and lots of salads and fish. “I give myself permission 20% of the time to eat whatever I want,” says Ritchson. “I’ll have a piece of pizza, and I don’t beat myself up about it.”

He even, after watching the documentary Forks Over Knives a while back, tried to give up meat completely. But this turned out to be a bridge too far. “I was like, ‘OK, I’m gonna go vegan,’” recalls Ritchson. “And I made it like four days. I was dreaming about ribs and burgers, and I’d wake up pissed off that I couldn’t have them. And then I broke. I was like, ‘No. Never doing that again. I’m a meat-eater. It’s just my blood type.’”

Tune in: Catch Blood Drive Wednesdays at 10 p.m. EST on Syfy.