A cross-country ski-inspired workout is gliding into Flatiron — no snow, goggles or lift ticket required.

NRTHRN Strong , the Scandinavian fitness brand that had Sag Harbor locals trading sunscreen for ski poles at a sold-out pop-up this summer, officially opens its first permanent US studio on Wednesday.

“The reception we received in the Hamptons this summer was incredible,” Nicoline Roth, the company’s founder and CEO, told The Post. “People were immediately drawn to the flow, power and results of the NRTHRN Strong modality.” 3

At the heart of the concept is a patented machine, created by a medical doctor and former cross-country skier, that delivers cardio, strength and mobility benefits.

“These three components are the core of longevity fitness ,” said Roth, who was raised

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