It was the fashion climax to the whole sweat-slicked, muscle-thumping show at the Forum in Southern California last month — Madonna on all fours, crawling cheetah-like down the stage in lustrous Lycra, with those thundering thighs and that winged hair. And it could mean only one thing: Leotards are back, baby.

The leotard, that vestige of disco nights and Jane Fonda days, is seeing new life in American Apparel stores, vintage boutiques and on fashion magazine covers, riding the same wave of 1970s and '80s nostalgia that brought the scourge of skinny jeans and leggings to the runways for fall.

"This has been a year of disco for her," says Madonna's stylist Arianne Phillips, who designed the costumes for the concert tour along with Jean-Paul Gaultier. "There have been lots of inspirations — everything from 'Saturday Night Fever' to 'Starlight Express' to 'Fame.' "

Still a fashion force at 47, Madonna wears several leotards in the show. And if you didn't already know that she works out three hours a day, it becomes abundantly clear when you see her jumping around like a modern Jack LaLanne, with nary a dimple in sight. At the opening of the disco portion of the show, Madonna rips off a white John Travolta suit with a flick of the wrist to reveal a one-shouldered unitard with ribbons of purple Swarovski crystals rippling across the torso, a replica of a costume worn by Abba in the late 1970s.

Then, for a finale, Madonna strips to something even skimpier — a smoky purple tank leotard, worn with flesh-colored fishnet stockings cut to the knee. Both styles were custom-made by Bill Hargate Costumes in West Hollywood, and Madonna gets fresh ones every week.

The leotard is named after French aerialist Jules Leotard, who debuted the body-clinging garment in 1859 when he performed his first flying trapeze act. His was a full-body, hand-knit jersey creation that stretched from the ankles to the wrists, more of a unitard, really. And legend has it that the way his assets were displayed was as much a part of attracting crowds to the Cirque Napoleon as his high-flying feats.

Performers in every arena, from ballet to burlesque, followed Leotard's lead, including showgirls who wore flesh-colored body stockings under their corsets so they would look flawless when they stripped down to (almost) nothing.

Male ballet dancers wore full-body leotards with short trunks on top until Vaslav Nijinsky left his off during a performance in Russia in the early 1900s, says Kevin Jones, curator at the Fashion Institute of Design and Merchandising in Los Angeles. "The czarina, who had a box close to the stage, had quite a shock."

But the origins of the leotard go back much further, to late-18th-century France, Jones says, when colored body stockings were the favored undergarments for the diaphanous, Roman-inspired gowns of the day.

Flesh-colored leotards once again turned up in lingerie drawers in the 1960s, when designers such as Pierre Cardin and Rudi Gernreich began making dresses with see-through cutouts.

But it was active-wear designer Bonnie August who brought the leotard into mainstream fashion during the disco era, helping to popularize the nocturnal uniform of a unitard or leotard with a wraparound skirt. An early proponent of using Lycra spandex, August created her most influential designs at Danskin. In 1979, People magazine ran a story on August with the headline, "Danskin Designer Bonnie August Has Got Almost Everybody Going Around in Next to Nothing." Her collections have been displayed at the Metropolitan Museum of Art in New York and the Experience Music Project in Seattle.

At the same time, leotards were becoming entrenched in popular culture. Venice, Calif., beachfront roller-skating had its own leotarded look, as modeled by Linda Blair in the so-bad-it's-good 1979 film "Roller Boogie." Rock 'n' roll style icon Stevie Nicks posed on the cover of Fleetwood Mac's 1977 "Rumours" album in a black leotard and ballet shoes, with a diaphanous Margi Kent dress on top.

Heavy metal has always had a heady relationship with unitards and leotards too: Freddie Mercury, David Lee Roth, Stryper. These days, the Darkness' Justin Hawkins is the keeper of that flame. Leotards and unitards are also the garb of superheroes, and thus many a Halloween costume.

No passing fad, the look continued in the mainstream because it suited a range of sizes, and complemented a growing interest in fitness. After Jane Fonda released her first workout video in 1982, women were always dressed as if they were coming or going to an aerobics studio. Olivia Newton-John got physical and in 1983, Jennifer Beals cavorted in an oversized sweatshirt, leotard and legwarmers in "Flashdance." Bodywear by Danskin, Carushka, Champion, Marika, Gilda Marx and Jacques Moret sold well throughout the 1980s and into the early 1990s.

At the same time, athletic leotards became more fashionable. At the Seoul Olympics in 1988, gold medal winner Florence Griffith-Joyner gained as much attention for her flamboyant one-legged leotards and fluorescent fingernails as for her record sprints.

In 1985, Donna Karan brought the leotard into the office as the bodysuit. With the ease of a T-shirt and the polish of a blouse, it smoothed out all the bumps and ripples on the body, giving women the freedom to climb the corporate ladder in their power suits.

The leotard and the bodysuit faded out of fashion in the late 1990s when the style mantra became 'the baggier, the better.' But with the fall 2006 season's new emphasis on a slim silhouette, the leotard is poised for a return to women's wardrobes.

Doris Raymond, owner of the Los Angeles vintage boutique The Way We Wore, received several inquires about leotards after Madonna wore a 1970s Danskin piece purchased at the store on the February cover of Elle magazine.

Raymond has acquired a few Danskins, as well as some Norma Kamali pieces — all from dead stock. "But with the resurgence of the 1980s, I'm looking for more."

And American Apparel, the hyper-sexualized, Los Angeles-based T-shirt empire catering to kids born long after leotards were fashionable the first time around, is selling four styles.

"An old girlfriend of mine came to me with a sketch last summer," says the brand's chief executive, Dov Charney. "It took a while for everyone to get it, but customers seem to be catching on now. It's just such a sexy piece."