German sportswear firm Adidas is underlining its commitment to struggling U.S. brand Reebok by stepping up a major marketing campaign that returns it to its roots in the personal fitness business.

Reebok, which had its heyday as the most popular U.S. sneaker brand in the 1980s when aerobics was booming, has suffered a steady decline that continued after it was bought by Adidas in 2005 for 3.8 billion US dollar.

That has prompted calls from investors for Adidas to sell Reebok, which has failed to help dent Nike’s dominance of the U.S. market. Reebok’s sales have shrunk by more than a third since the acquisition to 1.6 billion euros ($1.80 billion) in 2014, just under 11 per cent of Adidas group sales.

However, a move to focus Reebok back on its fitness heritage and away from team sports has started to work, helped by “Be More Human” ads launched in the United States in February featuring fitness fanatics dripping with sweat and mud.

Questions remain about Reebok’s weaker profitability than the core Adidas brand, but chief executive, Herbert Hainer, the architect of the Reebok deal, has said it would be wrong to sell it now, especially given the booming fitness market.

Reebok is rolling out the “Be More Human” slogan this week in Germany in its biggest brand-building campaign in the country, plastering billboards and running ads in dozens of gyms as well as inviting passers-by to try to flip a giant tyre, the campaign’s symbol.

“Be More Human” underlines Reebok’s shift in the last couple of years to tap into new fitness trends that are more group orientated than a solitary session on the treadmill.