NEW YORK (AdAge.com) -- Reebok has been credited with fueling the aerobics craze of the 1980s, and three decades later it's out to do the same with the toning category. The company's EasyTone footwear has captured a third of the billion-dollar market, said Matt Powell, an analyst at SportsOneSource.

The company doesn't break out sales of specific products, but Katrin Ley, head of the women's sport business unit at Reebok , said it has sold 5 million pairs of EasyTone in the U.S. and double that globally. Most EasyTone styles retail for about $100.

The toning category has been a key driver of business and contributed to four consecutive quarters of growth at the brand. Reebok, which is part of the Adidas Group, saw sales jump 25% in North America in the third quarter.

Reebok, like its competitors in the space, is rapidly expanding the line. EasyTone now encompasses shoes, sandals and boots, as well as a recently launched apparel line. The pants, shorts, capris, tees and tanks include "Resistone bands" to tone and strengthen muscles and improve posture by creating resistance when the wearer moves.

Ms. Ley expects the category will continue to see big growth in the U.S. and overseas. Overseas is a particular focus, given that the market is about a year behind the U.S. in its acceptance of toning products.

"It's a category that's here to stay," Ms. Ley said. "And the objective, from our end, is to establish Reebok as a thought leader and innovator in toning."

To that end, Reebok is readying an ad blitz from agency DDB. The effort is set to include TV, print, outdoor and digital and will likely have a significant media budget, as Reebok looks to maintain its share of voice in the category. Last year, Reebok spent $23 million -- or more than 80% -- of its total measured media budget advertising EasyTone, according to Kantar Media. In the first half of this year, new ZigTech products got some hefty investment, but Reebok still spent $10 million of its budget on EasyTone.