Under Armour is launching another star-studded advertising campaign as it continues its bid to overtake Nike to become the biggest athletics brand in the world.

Under Armour's $3 billion in annual global sales pales in comparison with Nike's $28 billion, but Under Armour is increasingly growing its share of the sector, recently overtaking Adidas to become the second-largest athletics brand in the US.

On Monday Under Armour unveiled its new marketing push, "Rule Yourself." In a press release, Under Armour said it aimed to "redefine what it means to be successful in training."

The campaign, created by the ad agency Droga5, stars quarterback Tom Brady, NBA MVP Stephen Curry, golfer Jordan Spieth, and American Ballet Theatre principal dancer Misty Copeland.

One of the Stephen Curry ads. Under Armour

A 60-second TV spot, which uses the soundtrack from the Philip Glass Knee series of operas, shows the athletes in training mode. They are then multiplied, becoming an "army" of clones, repeating their reps.

Adam Peake, executive vice president of marketing at Under Armour, explained the thinking behind the push in a press release: "The concept of the 'Rule Yourself' campaign is simple — you are the sum of all of your training. It's the only way to get better, and it's the common thread that unites each of our all-star athletes around the globe.

"Under Armour provides the footwear, apparel and equipment the athlete needs to push through a tough workout. But we also want to give them that extra inspiration to improve every day, to keep building their inner army, and to stay focused on success even when the going gets tough."

Golfer Jordan Spieth also stars in the latest Under Armour campaign. Under Armour

There has been a trend in recent months of sports-apparel brands and sports-related organizations creating big marketing campaigns to showcase the less-glamorous training element of sports, rather than just spotlighting athletes at the top of their game, at big marquee events.

Back in April, Nike launched its biggest-ever women's push with a campaign. The #BetterForIt ad aimed to encourage women to challenge themselves and expand beyond their comfort zone.

And earlier this year, the UK public body Sport England launched a much lauded campaign dubbed "This Girl Can," which showed women of all shapes, sizes, and abilities participating in sport to get fit.