Redheaded identical twins Katherine and Kimberly Corp, owners of Pilates on Fifth, a Stott Pilates studio, have unusual – and identical – resumes. The two, in their early 30s, are former Radio City Rockettes and professional dancers. They have matching undergraduate degrees in East Asian studies from Duke University and master’s degrees in international economic policy from Columbia University’s School of International and Public Affairs. Both are fluent in Japanese. But what makes the pair particularly distinctive in New York is that they are owners of the city’s only Stott Pilates studio.

Developed by Joseph Pilates in the 1920s, Pilates is a unique system of exercises designed to condition and strengthen the body; the Stott technique distinguishes itself from the traditional Pilates method primarily in how it regards proper spinal alignment.

“Joseph Pilates thought [the spine] was supposed to be ramrod straight, like a baby’s,” Kimberly noted of the late founder’s regimen. In actuality, she said, “the spine is intended to have natural curves,” a view espoused by Moira Stott, who revamped the Pilates program in the late 1980s after consulting with sports medicine professionals.

The difference was enough to convince the Corp sisters to opt for the latter approach.

“My sister and I have tight lower backs,” Kimberly said. “We can’t lie on the floor with our backs completely flat.”

After practicing Stott Pilates while touring with an international magic act, performing with the Rockettes, and completing their master’s degrees at Columbia, the Corp sisters decided to get certified as instructors themselves and open their own studio. They opened Pilates on Fifth in 2000.

“Kimberly takes care of human resources, programming, and quality control,” said Katherine. “I do the finances and the numbers.”

Located on the 22nd floor of 501 Fifth Avenue (just across the street from the New York Public Library’s branch for the humanities and social sciences), the joint enterprise has recently begun to attract an atypical clientele because of the sisters’ fluency in Japanese. This skill, polished when the duo spent four years abroad, first came to the Japanese public’s attention when Kimberly was modeling a Michelle Roth gown for a bridal special on Japanese TV two years ago.

To date, local advertising about the look-alike, bilingual instructors has been strictly word of mouth. Nevertheless, a steady stream of Japanese students has been enrolling ever since the TV spot. Some come as expatriates in search of an exercise program taught in their native tongue; others have been flown in by a host gym from Japan to be certified through the comprehensive, four-tiered teaching program. The demand has come as somewhat of a surprise.

“We don’t even have it on our Web site,” Kimberly said of the second-language option.

“Pilates in Japan is probably where it was in the United States in the late 1970s and 1980s,” explained Katherine. “The funny thing is with the Japanese, it’s going to pick up at a rapid pace because the whole idea of mind-body fitness fits their culture extremely well.”

If the boom at Pilates on Fifth is any indication, Katherine’s assessment will be correct. Already, the Corp sisters have been forced to hire a third Japanese-speaking instructor.

The twins recently finished taping a television series on the Japanese channel NHK (“the BBC of Japan,” said Kimberly) of 24 five-minute shorts in which the two explain and demonstrate their workout routine.

“How often do you meet redheaded twins who speak fluent Japanese?” Kimberly asked – presumably a rhetorical question.

For now, the Corps are concentrating their efforts on the home front. In February of this year, an additional classroom was leased down the hall to facilitate classes in mat, physioball, and BOSU (a sort of halved physioball that gets its acronymic name from its ability to be used BOth Sides Up). In August, Pilates on Fifth took over the building’s penthouse in order to provide the clients with a cardio workout area and the owners with a proper office looking out at the Chrysler building.

In September and October, all the spaces received fresh coats of paint: garrison red in the lobby, icy blue in the penthouse. Filmy plastic sheets of translucent mosaics have been layered atop the numerous skylights to ease the glare for clients who occupy the skyward-facing equipment.

Upstairs in the cardio room, each machine is equipped with a DVD player on which stationary runners can watch episodes of “Sex in the City,” “The Sopranos,” or another selection from the video library. Downstairs, the expanded changing rooms have added that most coveted of amenities: showers.

“You shouldn’t be paranoid about sweating during a workout,” Kimberly said.

How did the busy pair manage to find time to rethink the look of the space?

“One of our newer instructors also works on the side as an interior designer,” said Katherine.