Alexandra Waldman used to hate shopping.

As a plus-size woman, not only did she have to go to some far-hidden corner of the department stores on Fifth Avenue to find clothes that fit her — far away from the contemporary, so-called “normal” fashions — but she had to settle for matronly items shown on bulky, unattractive mannequins.

“It was a little painful to look at them,” Waldman, a former fashion journalist and finance marketer, tells The Post of the mannequins. “They were ham-fisted in the way you would imagine a Soviet wrestler at the Olympics to look: massive, beefy, instantly not associated with youth. It was everything that you dread with a modern plus-size woman.”

In 2015, Waldman and her friend Polina Veksler launched the minimalist label Universal Standard, which serves sizes 10 to 28, and, in late 2017, the mannequin maker Ralph Pucci approached the pair about collaborating on a new line of body-positive models.

Now, when Universal Standard — which sells directly to consumers online — holds pop-up shops throughout the country, they tote their specially-made Pucci figures with them.

“They’re very modern and abstract,” says Waldman of the Pucci forms, which have elongated swan’s necks and shapely, not zaftig, legs. “They have a fineness to them that makes them visually attractive in a sculptural way . . . Ralph’s mannequins don’t scream that they are ‘the other.’ They are part of the fashion story rather than the ‘fat’ story.”

The body-positive movement hasn’t just landed more full-figured and diverse women on the runways. It’s also changing the kinds of Fiberglas models we see while shopping.

Last month, the youthful fast-fashion label Missguided debuted an array of real-girl mannequins, featuring stretch marks, freckles and even the skin condition vitiligo, which causes patches of skin to lose their pigmentation.

Lord & Taylor and Saks Fifth Avenue have a rainbow of Afro- and natural-hair-sporting mannequins — done by Pucci and the artist Rebecca Moses — in its high-end designer shops.

And by the spring, Nordstrom is planning a full-scale overhaul of its mannequins in at least 30 of its locations, mixing robust size 12 and 16 models with the more “standard” 2s and 4s, as well as 8s — no more exiling plus-sizes to department store Siberia.

Nordstrom tells The Post that such changes are due to customer demand.

According to the Centers for Disease Control and Prevention, the average American woman’s measurements put her at about a size 14.

Meanwhile, according to a 2012 study by the Houston-based market research firm Plunkett, 67 percent of women in the US are considered plus-sized.

“I think that [brick-and-mortar] retail is not doing that well [financially] because it’s not embracing a lot of the people who are spending money on clothes — they’re ignoring them,” says Pucci, whose eponymous company sculpts its mannequins by hand in a Flatiron District workshop. “But I think they’re beginning to embrace diversity of all kinds.”

Mannequins didn’t always look like the minimalist wraiths we think of today.

When department stores first opened, in the late 19th century, the forms that donned the clothes for sale had curvaceous figures — with enormous busts and corseted waists — as was the style at the time.

But by the 1920s and ’30s, which brought about a more sylph-like ideal, saw mannequins get smaller.

By the time Pucci entered his parents’ New Jersey mannequin repair business in the 1960s — and decided to branch out into creating his own models — British manufacturers were pumping out waifish offerings based on Swinging Sixties It-girl Twiggy, complete with painted faces and polished fingernails.

“I decided we can’t compete with them because they’re too good,” says Pucci. “So we went the total opposite direction.”

In the 1970s, Pucci launched a range of abstract athletic mannequins — painted bold colors like bright red or forest green.

The company followed that up with a muscular collection based on Greek and Roman sculpture, just in time for the aerobics craze.

And as broad-shouldered “Dynasty” fashion boomed, and larger-than-life supermodels roamed the catwalks, mannequins got even bigger and more glamorous.

Stores commissioned bright-haired, exuberantly painted and diverse mannequins for their junior-clothing displays.

“Everyone was looking to be different back then,” says Pucci.

The 1990s changed all that.

Stores demanded standardized, minimalist mannequins painted glossy white or black.

Lisa Maurer, vice president of the French mannequin company Siegel & Stockman, which has been around since the late 1800s, says that manufacturers continued offering more diverse and larger-sized mannequins, but that stores weren’t buying them.

“We can make lots of different products,” she says. “But the market dictates what goes out.”

Yet, Maurer has noticed in the past few years that retailers have expressed an interest in changing the shapes of their mannequins — and requested a shift away from the burly plus-size molds of yore.

Sometimes that means paying more attention to details, such as making slightly larger heads and hands to balance out the proportions of a plus-size model, instead of just transferring those parts from a size 2 mannequin onto a size 16 one.

Sometimes that means adding ab definition — more Amazonian than Soviet lug — or some womanly curves, including what Maurer calls “a bit of booty.”

“You have the Kardashians posing for Calvin Klein, and we have a mannequin who looks like Kim, with what looks like a corseted waist, a healthy hip, a feminine shape,” she adds.

Mannequins also vary globally, depending on a culture’s beauty standards. The Venezuelan factory Eliezer Álvarez, for example, has taken to producing mannequins with bulbous boobs, perky butts and impossibly long legs, to reflect its cosmetically enhanced clients.

Fortunately, says Maurer, with 3-D printing and scanning, it’s easier and cheaper than ever to create more shapes and variations on the standard mannequin — no live models required.

For many shoppers who once felt alienated by the skinny waifs in the store windows, it’s a welcome change.

“The first thing you see when you go to a store is the mannequin,” says Waldman. “Seeing a mannequin who looks like you means that these clothes aren’t just for skinny women. It’s all part of a move in the industry toward inclusion.”