British consumers are buying sportswear in droves, with the almost £6bn market being driven by women, advances in wearable technology and the crossover between fashion and sports.

The UK market hit £5.91bn in 2014, up from £4.62bn in 2010, according to a report from Key Note. The research house estimates sportswear sales will total £8.65bn in 2019, based on current growth rates.

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But the data suggests the growth isn’t necessarily coming from new consumers, since sports participation is actually dipping. According to data from Sport England covering October 2014 to March 2015, 15.5m Brits took part in a sport once a week, down 222,000 in six months.

The UK is also getting fatter, with two-thirds of men and women classified as overweight, according to the Institute for Health Metrics and Evaluation. So what’s driving the trend?

Protein princesses

One reason for the market’s growth is that women now have more choice, both in terms of sports activities and clothing, according Key Note. The diversity of sports classes on offer, and better ranges for women mean female consumers can upgrade from the baggy gym t-shirt to more tailored, technical clothing.

Key Note highlights millennial women who follow fitness-obsessed celebrities on Instagram, keep a close eye on their diet, and go several times a week to the gym – cutely dubbed ‘protein princesses’.

Brands have recognised the importance of the female market, expanding their ranges for women. A number of new women-only brands, like Lululemon and Fabletic, have also emerged to meet demand for better, more technically advanced clothing.

Adidas-owned Reebok, Puma and Nike have also recently focused their marketing campaigns around women.

Reebok’s vice president for Western Europe, Chris Froio, told Marketing earlier this year that most major sports brands were just 30% targeted to women "at the high end".

He said: "At Reebok, we are at 40% women’s already, and we aim to make it 50% of our overall business. We have more initiatives around women’s fitness coming."

Sports vs fashion

Key Note also highlights the collision between fashion and sports, with more fashion brands launching ‘sports luxe’ lines. Conversely, more dedicated sports brands are dipping their toes into fashion, like Puma’s collaboration with Rihanna and Adidas’ tie-up with Kanye for his pricey Yeezy Season 1 range (pictured below).

Still, the fashion-sport relationship might not last for long, Key Note warns. 

The report noted: "This area of the market is heavily reliant on the fashion industry, which is very fickle and always changing, and there is a danger that when sports luxe and ‘athleisure’ trends lose their appeal within the fashion industry, sports fashion brands and sales among the leading competitors may suffer to some extent."

With sports participation on the wane, and fashion a fickle mistress, where might future growth come from?

Key Note predicts a boom in smart fitness clothing. Ralph Lauren last year debuted a smart shirt for athletes, which features built-in sensors that track the wearer’s movement and heart rate.

As a precursor to this, Nike and Adidas are investing in the connected runner. Adidas snapped up app makers Runtastic for £154m earlier this month, while Nike’s Nike+ ecosystem gives it access to huge amounts of consumer data.

 All of these are indicators that brands will develop more smart products for consumers, with Gartner estimating shipments will hit 26 million by next year.