Long gone are the days where the thought of gym wear evoked images of oversized hoodies and grey, Rocky Balboa-esque, sweatpants. Today, fitness isn't defined by what you do, but how you look while you're doing it.

The importance of having the hottest gear is a trend that retailers have been quick to capitalise on. Alexander Wang's collaboration with adidas has been a sell-out success and one that has been replicated from high fashion to the high street and everywhere in between (think Beyoncé's and Topshop's Ivy Park collection and Kate Hudson's Fabletics). It is this marriage of performance and aesthetics that has led to the birth of "athleisure".

With sales increasing by 42% over the last seven years, athleisure is now a £7bn market in the UK alone. Health and wellbeing remain a priority for consumers in 2017, with health club memberships in the UK increasing by 8.5% over the last 12 months. However, it is sales to non-gym bunnies that is turbocharging the industry. Fuelled by social media, the #instafit culture has driven around half of Britons to buy sports clothing for non-sports use, according to Mintel research.

It is an area that retailers ignore at their peril; in 2013 Levi’s boss Chip Bergh admitted the company was "scrambling" as it wasn't selling what consumers wanted in the wake of the athleisure boom and has since launched its stretch range to claw back market share. At the other end of the spectrum, JD Sports, the self-proclaimed "king of trainers", announced a 73% boom in profits last year as it realised the benefit of its exclusive rights to sell celebrity collaborations including Rita Ora's adidas range and Puma's Lucy Watson collection.

The sector will inevitably face challenges, from increased competition or the more extreme risk of an athleisure bubble being formed (according to Lululemon founder Chip Wilson). However, for the short to medium term at least, it is clear that the yoga pants culture is here to stay, so, sit back, grab a green juice and enjoy the ride.