Kino LorberTanaquil Le Clercq married choreographer George Balanchine in 1952 and contracted polio four years later, as recounted in “Afternoon of a Faun: Tanaquil Le Clercq.” (Kino Lorber)

Even through grainy black-and-white footage from the 1950s, Tanaquil Le Clercq’s allure is unmistakable. The famously lanky ballerina was a “stretched out path to heaven,” according to dance legend Jacques d’Amboise, and she was a muse and love interest for choreographers George Balanchine and Jerome Robbins. But, at age 27, Le Clercq suffered a fate fit for one of the tragic heroines she portrayed: One night she was dancing, and the next she was trapped in an iron lung after contracting polio.

The documentary “Afternoon of a Faun: Tanaquil Le Clercq” should be required viewing for dance fans. The old footage of Le Clercq, or Tanny as everyone called her, shows her performing with the New York City Ballet in such classic works as “La Valse,” “Western Symphony” and “Afternoon of a Faun,” and the Debussy-heavy soundtrack is transcendent. But director Nancy Buirski also tells a very human story about the ephemeral nature of youth and our need for reinvention.

There’s some pretty great gossip along the way, too.

Le Clercq’s French father and American mother divorced when Le Clercq was young, and her ballet-filled upbringing was anything but conventional. Balanchine first spotted her when she was 14, standing outside a classroom at his School of American Ballet with a pouty expression and arms folded across her chest. She had been kicked out of class and wasn’t shy about letting the renowned choreographer know.

Nine years later, the witty rising star would become his fourth wife, despite overtures from Robbins, among other men. A good portion of the film is devoted to the before-polio portion of Le Clercq’s life. The movie feels slow at times, but once the film focuses on 1956, the year the ballerina contracted polio, an emotional and gripping story begins to emerge.

Many of the City Ballet dancers had been vaccinated for polio before embarking on a European trip, and Le Clercq was in line to receive the shot. But she decided she would wait until after the tour. It proved a fateful choice; by the time she got home, she no longer could use her legs. It was devastating, and in one of the film’s most moving passages, we hear exactly how she felt — through her own lyrical words in letters to Robbins.

Le Clercq lived to age 71, more than four decades after her diagnosis. She never regained use of her legs, but she became a self-sufficient writer and teacher. Balanchine, meanwhile, is credited with keeping her going. He forced her to try things she didn’t think she could do and instituted a rehab regimen that included Pilates. But the choreographer also divorced her after falling for a 23-year-old Suzanne Farrell.

What’s most fascinating about “Afternoon of a Faun" — and what the movie could spend more time delving into — is ballet’s grueling and fleeting nature. At one point, a friend recounts how Le Clercq called her paralysis “a gift, in a way,” remembering the nausea-inducing stress of being a ballerina. By the time you’re on top, Le Clercq laments in a recorded interview, your body is already failing you. Ballet, even for a healthy dancer, isn’t a career with longevity. Like sports, it’s a young person’s game.

Yet, 14 years after her death, Le Clercq is still with us. She was a prototype for today’s dancers — the lithe ballerina who could do it all — and she inspired many classic works. The dancer’s career may have been cut short, but her legacy wasn’t.

★ ★ ★

Unrated. At the Avalon. Contains brief strong language. 91 minutes.