IT’S all Alexander Wang’s fault.
In 2014, the edgy designer launched a sporty line for high street giant H&M, telling the New York Times that it was inspired by the gym-to-street dressing he was seeing all over the world.
Despite admitting that he was far from an athlete himself, he said at the time “I live in gym clothes. When you go out on the street, it’s the uniform now.”
That same month, Nike CEO, Mark Parker, took the stage at the Women’s Innovation Summit in New York to declare, “leggings are the new denim.”
The madness took hold, and suddenly this new way of dressing had a name.
Athleisure was declared a hybrid of gym and street gear — clothing you could work out in before heading out for a cocktail at a swanky city-centre bar.
Tracksuits became joggers and running leggings became workout tights, which cost a couple of hundred euros.
Of course, celebrities jumped on the bandwagon almost immediately, with everyone from Jessica Simpson to Rita Ora launching a brand of luxe sportswear with a tagline that promised to take you from crossfit to the club.
Queen Beyoncé is the latest celebrity to launch a line, and Ivy Park speaks to every woman who has ever wanted to be in her BeyHive.
In a video launching the collection, she dances, runs and swims the collection, all the time looking like a goddess.
The singer explains that she named the brand Ivy Park — because of her daughter and the park that she learned to run in.
“I still go back to that park. Before I hit the stage, I go back to that park. When it was time for me to give birth, I went back to that park.
"The park became a state of mind. The park became my strength. The park is what made me who I am. Where’s your park?”
By the end of the short video, I wanted to buy everything in the collection and tell Beyoncé all about my own park.
So, what is it about athleisurewear that makes it so very appealing?
Deputy editor of Xposé Magazine, Aisling Keenan is delighted that it’s here to stay.
“As a woman who all too frequently prioritises comfort over fashion, I am delighted athleisure is a lasting trend,” she says.
“The fact that it’s perfectly acceptable — even fashionable, for me to wear trainers to work makes me insanely happy.”
Stylist Lisa Fitzpatrick agrees.
“I absolutely adore this trend. I wear my black Nike Roshe shoes with jeans, combats or jeggings almost every day.
"I love my workout clothing while doing jobs around the house or meeting friends for coffee or breakfast — there is such a huge variety of athleisurewear out there, there’s something for everyone.”
Former world indoor champion Derval O’Rourke thinks that the trend points to the fact that we all want to be more active these days.
“I like the trend — I think it actually encourages people to be more active,” she says.
“People are more likely to walk to work if they are wearing clothes that they look good and are comfortable in.
"I think activity is becoming very mainstream and people are naturally gravitating to these kind of clothes.”
Aisling Keenan agrees, citing our obsession with the gym as a reason for the sector’s popularity.
“I feel like the trend extended from the gym obsession that seems to have gripped Ireland,” she says.
“We’re all so much more conscious of health, fitness and our figures right now for whatever reason, and people were wearing increasingly more stylish gym gear.
“I guess it just spilled over into real life, meaning people could potentially go for breakfast and to a meeting in their athleisurewear and then work out in it too.”
But Lisa Fitzpatrick believes that athleisurewear in the office is a step too far.
“These clothes are about feeling relaxed, comfortable and gorgeous — just the way you should feel in the gym.
"I don’t agree with wearing this kind of stuff to the office.
"Wear it at home or out at the weekend, but be smart with your wardrobe for work — it will make you feel better.”
For the most part, athleisurewear is being marketed to a new generation of ambitious young women.
Ivy Park, in particular, seems to be a tribute to the strong, independent women Beyoncé encourages her fans to be.
Another strong woman is designer Stella McCartney whose collection for Adidas in 2004 was one of the first celebrity collaborations for athleisurewear and remains hugely popular, many collections later.
But you don’t need to wear a celeb-endorsed label to cut a dash in the gym or on the street.
As well as stocking Ivy Park, Irish company JD Sports has responded to the demand for athleisurewear by creating a bespoke range, called Pink Soda.
The range, available online on in its stores, is still in its infancy but is already showing signs of being one of the brand’s biggest sellers.
Of course, it’s all very well and good, getting very excited about dressing like a pop star on their day off, if you’re a size eight.
What about those of us who have a little more Beyoncé-style booty to shake around the gym?
What should we be wearing while working out to look amazing?
Aisling Keenan has a few tried-and-true tips up her sleeve.
“If you’re not as confident when exercising, I’d recommend doing the old double t-shirt trick.
"I wear a long, tight tank top which will hold me in, won’t ride up and covers up any love handles you need covered,” she says.
“Then I throw a looser T-shirt on over that and let it hang. I feel covered and held in all at once and it’s my go-to gym wear trick.
"I also wear leggings that I can tuck all my [tummy] rolls into, they go up to my belly button and beyond, which is not sexy but it works.”
She cites some althleisurewear as just too risqué for daily gym activity.
“There’s an aspect of being sculpted enough to get away with certain athleisure items,” she says.
“My personal adaptation of the trend is to stick to oversized sweaters and runners rather than backless tops over sports bras and hot pants.
"Although I do envy those who can work the skimpier stuff.”
Lisa Fitzpatrick is a rock of good sense when it comes to dressing larger sizes, having been there herself, dropping from a size 20 to 10.
“When I was 15 stone and started working out, I dressed around my size.
"I wore loose clothes — tops wrapped around my lower half, which covered my bum, and longer sleeves to cover my arms and make me feel comfortable.
“It’s not about the clothes. I’ve been there, and trust me, deciding to work out in the first place — that’s the big decision.”
Whether you want to wear athleisurewear for your TRX class or to swan around the local coffee shop, there is no sign of this mega trend abating.
From the highest-end designers, to almost every shop on the high street, there is a look to suit everyone, at every price point and every size.