Roberta Peters was a massive opera star in her day—and her day lasted for decades. For 35 years, beginning in 1950, when she was famously called on to take the place of an ailing performer at age 20, she was one of the leading lights of the Metropolitan Opera in New York City.

The singer was a great believer in the idea that opera was for everyone (here is one of many clips of her performing on the Ed Sullivan show), and Peters was likely showing her dedication to popularizing the art form when, in 1951, she allowed LIFE magazine photographer Michael Rougier to chronicle her fitness routine. Peters’ instructor was a supporting character in that story, but today his name is known to fitness devotees around the world.

For her instructor was Joseph Pilates. The fitness regimen that now bears his name is taught at gyms and training studios around the country. The pilates workout didn’t really mushroom in popularity until the early 2000s, but it is now everywhere, and its adherents include celebrities such as Hailey Bieber, Kendall Jenner and Bella Hadid.

At the time of the LIFE story the training method of Joseph Pilates was not actually known as “pilates,” but rather the term he had come up with for it, “contrology.” PIlates first made his name working with ballet stars such as Martha Graham and George Balanchine, so he was well-known in the New York arts world by the time he connected with Peters.

The LIFE article, headlined Diva With Muscle, described Peters as a longtime fitness fanatic, saying that “ever since she began taking singing lessons as a little girl in the Bronx, she has been making regular visits to the gym to build up her torso and strengthen her diaphragm.” Peters was so fit that the LIFE story said Joseph Pilates was “fond of asking strangers to feel her stomach, which is now `like iron.'”

Her dedication to taking care of her body paid off. She performed in recitals well into her 70s, before dying at age 86 of Parkinson’s disease. Pilates, who was born in Germany in 1883, would have been in his late 60s at the time of the LIFE photo shoot. He died in 1967, from emphysema, at the age of 83.

Opera singer Roberta Peters balanced her fitness trainer, Joseph Pilates, on what LIFE in 1951 called “her operatic breadbasket.”

Michael Rougier/Life Picture Collection/Shutterstock

Joseph Pilates training opera star Roberta Peters, 1951.

Michael Rougier/Life Picture Collection/Shutterstock

Opera singer Roberta Peters working with her trainer, Joseph Pilates, 1951.

Michael Rougier/Life Picture Collection/Shutterstock

Joseph Pilates training opera star Roberta Peters, 1951.

Michael Rougier/Life Picture Collection/Shutterstock

Joseph Pilates’ regimen for opera singer Roberta Peters included 20 squeezes with a springlike steel oval, 1951.

Michael Rougier/Life PIcture Collection/Shutterstock

Joseph Pilates training opera star Roberta Peters, 1951.

Michael Rougier/Life Picture Collection/Shutterstock

Joseph Pilates training opera star Roberta Peters, 1951.

Michael Rougier/Life Picture Collection/Shutterstock

Joseph Pilates training opera star Roberta Peters, 1951.

Michael Rougier/Life Picture Collection/Shutterstock

Joseph Pilates training opera star Roberta Peters, 1951.

Michael Rougier/Life Picture Collection/Shutterstock

Joseph Pilates training opera star Roberta Peters, 1951.

Michael Rougier/Life Picture Collection/Shutterstock

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