Young people are building fitness portfolios. Solidcore wants a bigger piece of them.

Solidcore is expanding its brand with a new class focused on heavier weight training.

Courtesy of Solidcore Boutique fitness brand Solidcore is beefing up with a new strength-focused class in infrared heat.

It's a big bet on resistance training as the future of fitness, with emphasis on longevity.

The balancing act is reaching new audiences without diluting what hooked loyal fans in the first place.

Solidcore is expanding beyond its signature workout for the first time in its nearly 13-year history.

When Solidcore launched over a decade ago, the brand found success with an intense 50-minute workout on Pilates-inspired resistance machines , known as reformers.

This winter, it will debut Ascend, a high-intensity, heated, floor-based strength training class, according to details shared exclusively with Business Insider.

The class will launch at Solidcore's upcoming Manhattan West studio, before rolling out to other locations.

Ascend puts heavier weights and progressive strength training at the center of its workout, a direct appeal to people who want to build muscle.

It also features a new infrared heating system, tapping into emerging research that training with heat may offer heart-health and anti-inflammatory benefits.

The move reflects a broader shift in boutique fitness.

The studios that made their names by specializing in a single type of exercise are confronting a new type of customer: one who lifts, runs, does Pilates, tracks their fitness metrics , and increasingly thinks about exercise as an investment in their bodies, rather than going for aesthetics.

"Consumers are more savvy now.

They're talking about longevity, recovery, wellness, not so much calorie burn," CJ Zarb, founder of The Pilates Journal, told Business Insider.