To say Twyla Tharp is still at it after all these years would be inaccurate. Because there is never anything still about Twyla Tharp.

The title of the new PBS documentary about this seminal figure in modern dance — who has sent bodies of all shapes into orbit and even made Mikhail Baryshnikov go artfully wobbly in the knees — puts it nicely. "Twyla Moves," it's called. A survey of Tharp's origins and the evolution of her restless aesthetic, Steven Cantor's film takes the measure of the choreographer's career as she approaches her 80th birthday. Still creating dance, even in the isolation of a pandemic-enforced quarantine.

"What I'm doing now is working with 17 dancers in a company I have never seen," Tharp says in a recent Zoom interview from her New York apartment, where she has been engaged in online rehearsals of a new ballet for a troupe in Germany.

That Tharp would use the shutdowns to unlock her imagination further does not come as a surprise. Nor does the fact that she's never met in person the dancers and technical people she's working with.

"She has been so uniquely focused on dance her whole entire life, at the expense of everything else, that there was not really that much else to dredge up," Cantor says.

"Twyla Moves," which is part of the long-running PBS series "American Masters" and can be viewed at pbs.org, trains a lens on the perspicacious intellect and personality that frame the Indiana-born Tharp's dance worldview, and on a body of work that stretches back to the 1960s.

The choreographer's eclectic inspirations wind like a scenic highway through American culture, from ballet to figure skating, from Frank Sinatra to Philip Glass. Cantor dips into Tharp's remarkably complete film archive for glimpses of her earliest explorations of minimalism with a group of female dancers that included Sheela Raj, Theresa Dickinson, Rose Marie Wright and Sara Rudner.

The grainy footage of Tharp in a rehearsal room with a young Baryshnikov in the mid-1970s gives way to clips from Milos Forman's film adaptation of "Hair," for which she devised the dervish-like movement. A significant moment is devoted, too, to "Movin' Out," the 2002 musical based on Billy Joel's songbook that Tharp directed and for which Broadway bestowed on her the Tony Award for best choreography.

Tharp, who founded Twyla Tharp Dance in 1965 and went on to choreograph for the Joffrey Ballet, American Ballet Theatre and the New York City Ballet, is a titan of contemporary dance: She received a Kennedy Center Honors in 2008, alongside Barbra Streisand, George Jones, Morgan Freeman and The Who. But she turned down the producers of the retrospective "American Masters" franchise several times, perhaps because it was something she thought could wait, as she put it, "until I was dead." The pandemic changed Tharp's mind, though, especially after she considered that Zoom could be a choreographic partner.

"This distance activation was the only way I was going to be working this year," Tharp says she realized. "So it was like, 'OK, I'll do your PBS show. But half of it is going to be new work.'"

"Twyla Moves" is filled with images of Twyla moving: performing in 1969 amid paintings and sculptures at the Metropolitan Museum of Art with the women she lovingly calls "the bunch of broads"; over the shoulders and under the legs of Baryshnikov in 1975; and in her studio today, exercising, twisting, bending, demonstrating the steps she expects dancers a third of her age to execute.

"I'm in remarkable physical condition," she says. "I find that to work I need to maintain myself. I've always pushed myself to a limit beyond which others do not go."

"She pushes people to enormous extremes outside of their comfort zone," says Cantor, who logged 75 hours of Tharp on film over seven months.

For the 80-minute documentary specifically, Tharp decided to work on a new, compressed Zoom version of her 2012 piece "The Princess and the Goblin," with a cast including Herman Cornejo, Maria Khoreva and Misty Copeland, a muse of Tharp's and American Ballet Theatre's first African American principal ballerina. The film records a process that is, for a viewer, conceptually challenging: how one might dream up the synchronous gestures of four people in four remote spaces and, at the same time, deal with the sound lags and interruptions of fickle internet connections.

"She spent a lot of time thinking it through and dancing it herself and thinking what step would lead to the next step," Cantor recalls. "And how two people in two different screens in two different parts of the world look dancing together. She spent hours and hours and hours behind the scenes, just trying to work it out herself."

Cantor's camera catches Tharp in her studio, instructing sweaty faces on computers: the art of making art, byte by byte.

"It's going to be a huge shock to the performing industry, that the digital world is a reality, that people are going to continue to connect to the arts through this device," Tharp notes during our Zoom exchange. "To a greater or lesser degree, it's not going away. So to learn how to utilize it and be challenged through it, has value.

"You can't be frustrated," she adds. "You can't be missing what ain't there. You got to see what is there."

Unlike the ballet Tharp has been working on with the German company, which debuts this month, the three-minute dance she created on "American Masters" was cast with dancers she has known for years. "So it's like I knew that I had seen them," she says. "I knew them tangibly. I know how much space they occupy while they're in two dimensions."