A fresh take on an old-school workout promises to make you long and lean—pronto.

Article By Nicole Catanese | Featured on Harper’s Bazaar

Die-hard spinners are jumping off their bikes and on to … rowing machines? Yes, it’s true. Call it the fitness trend that no one predicted, but suddenly boutique rowing studios are opening at a fast pace across the country and loads of converts are swearing off cycling classes. “I drank the Spin Kool-Aid like so many—but after a year I plateaued and no longer saw the results I wanted,” says Hilary Rainey, 26, a manager at a nonprofit. She’s a regular at New York’s CityRow studio, going twice a week, and has lost 11 pounds in just under two months. Jessica Luftig, 38, a project manager, has gone three to four times a week religiously since February in lieu of TRX Suspension Training and barre-toning classes and dropped 25 pounds. “I can’t get enough,” she says.

Here’s why: Rowing just might be the most efficient exercise ever. “With each stroke, pretty much every part of the body is used,” says Stella Lucia Volpe, an exercise physiologist and professor of nutrition sciences at Drexel University in Philadelphia and an avid rower. And it may let you skip crunches—for good. “A big part of rowing is core strength,” she adds. “People think it’s all arms, but rowing is much more legs and core.”

CityRow founder and CEO Helaine Knapp decided to line a loft with rowing machines after losing weight and making her own body “tight” with a rowing machine at her local gym. She hired a team of fitness pros to create a 50-minute high-intensity interval-training workout (which alternates between the rower and the mat), and opened CityRow last January. Classes are often wait list only.

Similar to indoor cyclists, rowers are meant to stay in sync with one another, as they would if they were gliding across the water. However, unlike Spinning’s call for 95 percent legs and 5 percent upper body, the rowing ratio is more along the lines of 60 percent legs and 40 percent upper body. CityRow’s mantra (“legs! core! arms!”) is repeated again and again throughout each 30- to 60-second sprint.

“Rowing is a full-body exercise, and it keeps the heart rate elevated,” says Garrett Roberts, an exercise physiologist and personal trainer who founded GoRow Studiosin Hoboken, New Jersey. “But then it’s leg press after leg press and row after row, so there’s a huge strength-training component to it too.”

Which is why you’ll get a svelte physique faster. “Rowing burns two to three times the amount of calories of Spinning,” explains Roberts. “Unlike a bike, which only has resistance in one direction, rowing has resistance in both directions—forward and back—making you much stronger and increasing the rate at which you burn calories.”

Josh Crosby, a former competitive rower and a co-creator of the WaterRower GX(a.k.a. Indo-Row), a rowing machine outfitted with a water-filled flywheel, says that the GX not only adds natural resistance but also allows you to hear the swoosh of water with every pull. Crosby, along with fitness pro Jay Blahnik, incorporated the modern rower into ShockWave, a class developed for Equinox gyms. In addition to the stellar calorie burn (up to 800 calories an hour), the workout has a secret perk—perfecting your posture, says Gregg Cook, a ShockWave instructor at Equinox in New York. “Most people are hunched forward over their desk all day,” he notes. “This wakes up all the muscles in your back.”

Ironically, just as the rowing machine is transitioning out of the water, the stationary bike is being submerged—in what looks like a personal Jacuzzi. At London’s Hydrofit spa, clients like Pippa Middleton (famous for her rear view) pop on headphones and watch TV or listen to music as they pedal away. Devotees at Waterbike outposts in France (and a few other European countries) also “ride” for 30- or 45-minute sessions with pulsing water jets—thought to rev up circulation and banish cellulite—that are aimed at dimple-prone areas, i.e., the butt and thighs.

But back to why weaving rowing into your workout repertoire is a must (even House of Cards‘ fantastically fit Claire Underwood has taken up rowing in place of her beloved running). “Rowing truly uses every part of the body,” Volpe says. So you can spin like crazy in water—or a vat of oatmeal, for that matter—and it won’t even come close to the results you’ll get from rowing.