David Harbour running on the street

David Harbour “Developed A New Relationship” With His Body After Massive Weight Loss Transformation

The ‘Stranger Things’ star opens up about his on-screen transformation.

When fans tuned in for Season 4 of Stranger Things, David Harbour was almost unrecognizable from the big-bellied cop in Season 3. The 47-year old actor–who plays Police Chief Jim Hopper–sported an impressive six-pack and chiseled jaw–the result of his 75 pound weight loss transformation.

Harbour says his new physique—which he credits to eight months of intense training and intermittent fasting—changed his relationship with his body, and his outlook on life.

“It opened up a whole new world, [I’m] a lot more pliable and a lot more teachable, even in my mid-40s, than I ever imagined it could be. And it felt like a rebirth,” Harbour told PEOPLE in an exclusive interview.

Weight Loss

Prior to his weight loss, Harbour felt like his health was heading downhill.

“There was a moment where I was crossing the street in New York and there was a car coming and I thought, ‘Oh, I gotta sprint a little bit across the street,’ and I just couldn’t sprint,” Harbour said. “And I was like, ‘Oh I guess that’s gone. I guess I’ll just never sort of run across the street.’ I mean at this point I was like 270 pounds and my knees were kind of shot.”

“I just sort of thought that that’s the way life was, that was the trajectory of your body,” he says.

Celebrity trainer David Higgins created Harbour’s fitness plan, which involves strength training and low-intensity cardio at least four to five days a week.

Harbour says he developed a love of running, which led to a new partnership with Brooks Running for their new “It’s Your Run” campaign.

“To have a campaign that really fit me and my style of how I approach running, I just thought that was a very welcoming, a nice way to look at fitness in a world of all these experts, in a world where I’m constantly being barraged about how to do an exercise and how I’m doing it wrong, to have this attitude of like, it’s a playful thing and it’s your run and you can go out and do it any way you want to do it,” Harbour told PEOPLE.

Harbour isn’t fully “settled” on where’s most comfortable with his weight, but he feels “pretty good” about his journey so far.

“I love my big body as much as I love my lean athletic body,” Harbour says. “Something about being an actor is you are allowed to live in different skin and I like being a chameleon in that way.”