The original Hula-Hoop girl is sitting in a café wearing a leopard-lined jacket, gold-painted nails, and Revlon lipstick in a shade called Orange Flip. She is blonde, fit, and incredibly bubbly at 94 years old—exactly the vision you’d expect of the muse who inspired the biggest sensation to hit the U.S. toy business. (And not too unlike the model Karl Lagerfeld sent down a Spring runway a few seasons back clad in a one-piece mesh bathing suit, holding an oversize Hula-Hoop beach bag.) Except that until recently, no one even knew she existed.

Hula Girl is a short documentary by Amy Hill and Chris Riess, playing at the Tribeca Film Festival, that sets out to debunk the myth that the Hula-Hoop—which made $100 million for the toy manufacturing company Wham-O in its first year on shelves in the spring of 1958 and launched a fitness phenomenon in the process—was invented by two male entrepreneurs from California. In fact it was Joan Anderson, an Australian maverick who left home for Hollywood in 1946 to take up modeling and rub shoulders with Marilyn Monroe, then a brunette Norma Dougherty, and brought the first hoop stateside.

It was made of bamboo and “fun for the whole family,” she says, her voice crackly, her mind as sharp as a tack. After discovering it in Sydney while visiting friends—“I heard laughter coming out of a back room at a party,” she says, “and there they were, with this bamboo hoop, having such a great time”—she returned home and asked her mother to mail her one of her own. Not long after, she and her husband, a former fighter pilot turned businessman with experience in the toy business, began to show it off at dinner parties, leading one guest to announce that Anderson looked like she was doing the hula, the hip-swerving, core-building dance developed in Hawaii. Anderson’s husband introduced the device and name to Wham-O’s cofounder Arthur “Spud” Melin, a man with whom he had done business before; a man he had trusted.

Just like that, the low-impact, aerobic exercise spread like wildfire across California fairs, making it “the standard against which all national crazes are measured,” wrote Richard Johnson in his book, American Fads. But with no contract in place (“We didn’t sign any paperwork or anything, it was a gentlemen’s handshake,” she says) and no one returning their calls, Anderson and her husband were forced to let the hope of future royalties go. (They later settled with the toy company for a small fraction of what they would have made in the first year alone.) “Life goes on,” she says, claiming her real fortune as her four children and one husband of 62 years. “We had a wonderful life.”

So what’s the secret to staying as nimble and mentally sharp as someone half her age? For Anderson, it’s found in her lifelong passion for movement and adventure. She still swims three days a week, Monday, Wednesday, and Friday; she stretches and strengthens on Tuesdays and Thursdays; and regularly walks and gardens, not to mention attends ballroom dancing class once a week. “I went boogie-boarding last summer,” she says, more matter-of-fact than proud. “And I zip-lined on a family trip in Catalina a few years back.” As for hooping? “I do it once in a while for exercise, but not as much as I should,” she says of the workout that, more currently, has been embraced by modern day fitness buffs like Michelle Obama and Marisa Tomei—the latter of whom relied on it to get in “stripper shape” for the 2008 drama The Wrestler, and has been hooping ever since. “I used to be able to start it around my neck and work on down,” says Anderson, demonstrating with the slightest swivel of her hips, as if the hoop never left her side.