Gyms have been moving their equipment into classes for a few years now, from SoulCycle’s stationary bikes to the recent spate of treadmill studios. Now a new star is emerging — and it could be the best workout yet.

“If I was locked on an island with only one piece of equipment to keep me in shape, rowing is what I would be doing because it does hit everything I need,” says Eric Von Frohlich, co-owner of the boutique studio Row House.

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Rowing was actually his dirty little secret back when he was a cycling instructor 10 years ago. “I needed something that was a little more full-body,” he recalls, so he sought out CrossFit, which led him to rowing.

He opened Row House in March 2014 with his wife and business partner, Debra Strougo Frohlich, and they’ve just expanded to a second location last month. On the lines of gleaming Concept 2 machines, they teach classes focused on rowing intervals. They promise a strength and cardio workout that engages 88 percent of the body’s muscles and burns up to 600 calories per session.

“The reason we really got into rowing is we saw across the board how helpful it was as a piece of apparatus for so many different points in life and for so many different populations,” explains Debra. “And especially because we are New Yorkers and we’re time-starved and at the end of the day it’s the most efficient workout there is.”

If you’re starting from zero

Everything about the rowing experience is controlled by the user; Debra calls rowing the cardio version of yoga or Pilates. The pace is set by the user — the machine doesn’t keep moving when you stop, like a treadmill or spin bike — and risk of injury is minimal because your feet are strapped into place and your knees and ankles remain aligned, with no chance of twisting or torquing.

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“It really comes down to what you want to put into the activity,” says Eric. “You’re not limited by the equipment; you’re limited by your fitness level and your ability to push as hard as you want to push. And that’s something that’s kind of beautiful and unique about it.”

If you’re trying to lose weight

Whether you have a little weight to lose or a lot, exercise can be unpleasant for many reasons. The constant jiggle of extra fat is not only uncomfortable but can be embarrassing, while the simple fact that you’re carrying around more weight is tough on joints that would already be stressed by workouts like running.

On a rower, you’re not only sitting — on a seat that’s much larger than a spin bike — but the motion is virtually no-impact and your center of gravity is low, keeping you more stable.

“When you’re on a rowing machine, you don’t have gravity pulling down on you that way,” Debra explains. “You don’t feel like you’re putting stress on your body; you feel like you’re almost weightless.”

Why take a class

Some rowing enthusiasts find they get into a zen headspace — Debra Strougo Frohlich calls it “almost meditative” — but many find the repetition monotonous and give up due to boredom. A rowing class adds a social aspect, creates a high-energy environment and mixes rowing with other exercises.

The classes at Row House, with beginner and experienced levels, have participants get off the machines for intervals of squats, lunges, stretching of the hips and hamstrings, and push-ups. “What we’re doing off the rower is building up your ability to spend more time on the rower,” she says.

If you sit all day

Sitting is the new smoking, as study after study has shown, affecting everything from brain function to raising your risk of diabetes — so more sitting may seem counter-intuitive. But that’s how rowing targets some of the problems that people who sit for most of the day can develop. “The [rowing] motion is something that just about everyone needs, which is posterior strength and opening/closing of the hips,” says Eric.

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When you push back on a rower, you’re loosening up your tight hamstrings, sitting at the optimal 90-degree angle and engaging the shoulder, back and core muscles. (Despite how it looks, the effort of rowing comes 60 percent from the legs, 30 percent core and just 10 percent arms.) It all adds up to better posture while seated, standing taller and reducing stress on the neck.

If you’re looking to get toned

Debra stopped doing spin classes and put on almost 40 pounds during her last pregnancy four years ago. When it came time to get back in shape, she found that rowing not only improved her out-of-whack posture but could do what the bike could not.

“Once I got used to the rowing machine, I saw that it was getting all the hard-to-reach areas that a spin bike just never gets,” she says. “You continue to strengthen your legs, your core and your upper body, which is really what you need for life, granted, but also for carrying a new baby.”