If you watch Riverdale, the CW’s reimagining of the classic Archie comic book series, you know the show packs more of a punch than you might expect from its retro source material. Instead of leaning into a buttoned-up 1950s-era aesthetic, the depiction of the fictional town is a true 21st century pulp, filled with fit actors like KJ Apa, Hart Denton, and Charles Melton, who take seemingly every excuse to show off their muscles onscreen.

Much of the show’s cast can credit their physiques to Alex Fine, a personal trainer with a diverse client list. Fine has trained everyone from Mile 22 and Friday Night Lights director Peter Berg to NFL stars like Odell Beckham, Jr. in his short career—but he says the group from Riverdale bring a particular energy to their workouts. “The Riverdale guys are one of the hardest [working], most competitive group or collectives that I’ve gotten to work with,” Fine told Men’s Health when we met up at Performix House in NYC.

The cast members work out (and sometimes, live) alongside the trainer in Los Angeles, so he’s intimately familiar with the energy the actors bring to the highly-rated show. To show us how the Riverdale crew attacks their training, Fine shared one of his go-to workouts, which he calls The Saturday Swole. “It’s a quick and easy pump that we get through right before the weekend if you’re going to a pool party or the beach or whatever,” he says.