Anyone who’s suffered through ballet class knows you can’t dance without engaging your back.

But though a dancer’s back muscles are hard at work, all audience members see is the seemingly delicate arm movements and positions in front.

It’s an illusion disrupted by Eva Stone’s new piece, “F O I L,” commissioned for Pacific Northwest Ballet’s “Locally Sourced” program.

“Locally Sourced” is being performed through Sunday by Pacific Northwest Ballet at McCaw Hall, 321 Mercer St., Seattle. Tickets are $30-$190. For information, call 206-441-2424 or visit pnb.org.

In the section of “F O I L” titled “Be Still,” soloist Margaret Mullin and corps de ballet dancers Cecilia Iliesiu and Emma Love Suddarth stand side-by-side, clad in gigantic romantic tutus, their apparently naked backs to the audience.

Before dipping into the dramatic forward tilt that ends the section, Mullin, Suddarth and Iliesiu do little but engage their arms, and when they do, their back muscles also engage and release in a way that’s visible to the audience.

Not much else happens in this section, but it’s what sold me on Stone’s piece. Classical ballet is designed to minimize the appearance of strain: Dancing is pure effort, but it’s concealed to preserve an ideal of beauty rooted in tradition.

So to see a dancer from behind, to see her back muscles in play, is to witness, perhaps for the first time, the strength and discipline that underpins all ballet.

Stone’s piece also tasks the dancers with announcing the names of each section of the performance — abstractions like “Now,” “Exhale” — and the raggedness of their words is a backstage pass into the very real exertion of their bodies.

In this way, Stone’s piece is deeply generous. She’s letting us behind the curtain into what the act of dancing is really like. It’s also unapologetically pretty, with chandeliers and flowing costuming. With its slate of women composers and all-women creative team, it’s also a feminist project and a corrective to the dance world’s well-documented failure to engage women artists.

“F O I L” is one of three world premieres commissioned from local dancemakers for “Locally Sourced.” The others are from Spectrum Dance Theater’s Donald Byrd and PNB corps de ballet dancer Miles Pertl.

Byrd — in pieces like last summer’s resonant “Strange Fruit,” a performance about lynching and the specter of racist violence — typically combines technically beautiful dance and examinations of social justice.

The latter is not in evidence in “Love and Loss,” Byrd’s piece for PNB, but the former is, along with the choreographer’s usual gravitas and deep feeling. (A friend texted me after she’d seen it: “Donald Byrd, what a legend.” I’m inclined to agree.)

“Love and Loss” employs classical dance steps in a meditation on romance and its discontents, pulling strong performances from key corps members like Amanda Morgan and Iliesiu, and soloists Angelica Generosa, Kyle Davis and Dylan Wald. (Maybe skip this one if you’re going through a breakup.)

The final piece of the evening, Miles Pertl’s crowd-pleasing “Wash of Gray,” is a tribute to Seattle, and one that seemed well-received by the audience on opening night.

Though it lacked the cohesion of Byrd and Stone’s pieces, it took a number of interesting risks, the most successful of which was the decision to feature a solo from corps de ballet dancer Sarah Pasch, who is 28 weeks pregnant.

At times, the content felt too literal to look past. But Pasch’s solo cut through the noise, and made me wonder what Pertl will do next.