News of Gigi Hadid -- one of the hottest models of the moment -- becoming a Reebok brand ambassador went viral in a matter of minutes. Although this latest pairing may have taken fans by surprise, Gigi Hadid is by no means the only catwalk star to sign up to sportswear, which has real pulling power for models right now. So what's going on? Here's a look at how this fashion/sportswear crossover came about and how the trend looks set to develop.

The worlds of fashion and sport appear to be on a collision course, as brands like Puma, Nike, Adidas and Reebok line up celebrity collaborations. Now even models are keen for a slice of the action, as the traditional goal of a brand ambassador contract with a couture fashion label is shifting to favor major sportswear brands, which have regained the heights of public popularity over the last few years. 

Kylie Jenner, Cara Delevingne, Naomi Campbell

While models are lining up to pose for sportswear brands, the labels themselves are also only too happy to sign up stars of the runway, who are now almost as popular as sporting icons. 

As well as bringing sneakers back into vogue, sports brands have successfully launched into fitness fashion, two segments that models know inside out. And so, the industry's heavyweights have spared no expense to sign up the services of the most popular models of the moment.

In the space of just a few seasons, Puma has bagged Kylie Jenner, Liu Wen, Naomi Campbell and Cara Delevingne. Nike -- usually known for collabs with sports stars -- has signed up Joan Smalls and Cindy Bruna through exclusive partnerships with luxury labels, while Adidas has teamed with Karlie Kloss, Lexi Boling and Sara Sampaio.

The latest brand to score a big name signing is Reebok, with the sublime Gigi Hadid. Bella's sister slipped on a pair of boxing gloves for the brand's latest campaign. Fashion addicts are already wondering what the labels have in store for the coming seasons, as competition hots up in the sportswear arena.

Following the lead of celebrities

Models' sudden taste for sportswear brands hasn't come out of the blue. Global celebrities trod the sportswear path long before runway queens. Rihanna, for example, has been a creative director for Puma since 2014, with a hit Fenty x Puma by Rihanna collection. Such celebrity collaborations have helped draw models into the world of sport.

The Barbados-born singer isn't the only celebrity joining the party, as rapper Kanye West has teamed with Adidas Originals to design sneakers and a clothing line.

The buzz surrounding sportswear has filtered into catwalk styles over the last couple of seasons, with sporty silhouettes featuring sweaters, track pants, sneakers and outdoor wear spotted on the runway. Fashion houses have also jumped on board the trend, notably with NikeLab. 
Givenchy creative director Riccardo Tisci and Balmain's Olivier Rousteing have both teamed with the famous American brand.