The retail apocalypse is killing fashion as we know it as a new dress code takes hold in America

The way the average American dresses has changed drastically in recent years.

Evolving dress codes, comfortable and technologically improved fabrics, and stylish but sporty designs have all combined to carve out a large section of the retail market.

Sales for activewear in the US reached $45.9 billion in 2016, according to NPD Group data. That's an 11% uptick from the previous year, and far greater than the growth of the apparel sector as a whole.

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The rise of athleisure as the dominant way that people dress has broad implications for the rest of the apparel industry. As people are opting to move away from traditional styles and dress in this utilitarian style, fashion brands that have been slow to jump on the activewear bandwagon are suffering.

That means that traditional fashion brands now have less of a say in how Americans are dressing. Fashion is dying. Athleisure is now king.

Athleisure is here to stay.

"Athleisure is the new casual," Deirdre Clemente, a professor of history at the University of Nevada, Las Vegas, recently told Business Insider.

"Athleisure" is commonly defined as a "weird hybrid" of business casual and athletic wear, which has created an entirely new category of clothing. It's combining two trends that have dominated American casual clothing — durability and comfort — in a versatile way.

"I don't think athleisure is going anywhere, honestly," Clemente said. "It'll only get bigger and more accessible to more people, and more acceptable in more environments."

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An overall easing of dress codes allows athleisure to be worn more often.

Theory is all well and good, and sales data tells a compelling story. But we wanted to see how these trends spell out for everyday people, so we took to the streets of New York City to ask average people why they're wearing activewear in the middle of the weekday.

Their answers are illuminating, and they support the data with portraits of how athleisure is worn in the real world.

This spells trouble for retailers that haven't adapted.

Over 3,500 stores are expected to close their doors in the US this year, Business Insider's Kate Taylor reports. Mall visits declined by 50% between 2010 and 2013, according to the real-estate research firm Cushman & Wakefield.

Some of the closing stores are locations of America's most iconic fashion retailers, like Macy's, Sears, and Payless — each of which are closing dozens to hundreds of stores in 2017.

Business Insider/Sarah Jacobs

As general mall traffic declines, e-commerce becomes a bigger threat, and fashion brands continue to put out designs and clothing that don't resonate with consumers, these store closings will continue.

This mindset has customers reconsidering rental.

As purchasing habits change, less of consumer spending is going toward formal apparel. Major events still sometimes require such clothing, however.

Enter rental apparel. A new wave of rental-done-differently companies have shifted both the landscape and the stigma surrounding rental garments. With a focus on service and luxury, companies like Rent the Runway and The Black Tux are making a compelling case for consumers to eschew buying luxury formal garments like tuxedos and cocktail dresses altogether.

Facebook/The Black Tux

In this new reality, brands are not seeing the benefit of stalwarts like the fashion show.

As social media becomes more of a factor in the way brands communicate with consumers, some are now looking at the fashion show as an unnecessary expense. Fast-fashion retailers are creating an additional challenge for high-end brands, as they often copy runway styles on a quicker timeline and at a cheaper price point.

Many brands are electing not to show, cut back how many times a year they show, or only show in certain cities.

Fashion as we know it is dying.

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