Tiger Woods costs $20 million a year. David Beckham, £10m. In these troubled economic times, sportswear manufacturers may find themselves having to reevaluate such costly celebrity endorsements, but fortunately for them the world's most popular gym fanatic has stepped in to offer his services. Cost: $0 for four years, with the possibility to extend in 2012.

The media fascination with Barack Obama's sporting antics is a boon for makers of leading athletic brands, which the president-elect has been pictured wearing on frequent trips to the gym and basketball court. The current presidential favourite appears to be Nike, the famous tick spotted on Mr Obama's attire so regularly that one would be forgiven for suspecting a product placement deal.

Not so, says Nike, but nevertheless the company is pleased that so stylish a figure favours its products.

"We don't make a point of giving the president-elect any products for free, but we're glad that he has such good taste in sportswear, whether he's working it out or taking it easy," Nike spokesman Charlie Brooks unashamedly told The Times.

When Mr Obama strolled down a Hawaii beach in August, it was a Nike t-shirt that he wore. When he showed off his basketball skills in a school challenge in April, his trainers bore the distinctive logo. On occasions he has turned himself into a veritable walking billboard, sporting Nike from head-to-toe.

However the President-Elect has been careful not to show too much favour to the Portland-based brand. Perhaps a little controversially, the Japanese brand ASICS seems to have recently replaced Nike as Mr Obama's footwear of choice. Pictures of post-election gym trips have shown him wearing the ASICS Gel Nimbus 10, a new model which retails for around $120 (£80).

ASICS, less well known in the States than its domestic rivals, described itself as "thrilled" with the endorsement.

Eóin Treacy of ASICS UK said: "Barack Obama is said to pick only the best and brightest for his team and he's certainly done that with his footwear."

The North Face, the California-based outdoor wear company, has also benefited from a presidential endorsement. Pictures of Mr Obama in one of their fleece jackets were splashed across the pages of the world's newspapers after he wore it to take his daughters to school just five days after his election victory; he was pictured wearing it again on a gym trip the following week.

Such photo opportunities can be worth millions to sportswear companies, according to branding experts.

Nigel Currie, Director of Sports Marketing at Brand Rapport, said if a brand featured in iconic photos of the President-Elect that appeared over and over again, it could theoretically boost their profits by "hundreds of millions". However he noted that Mr Obama's tendency to mix up his logos could detract from the impact.

"The right photo opportunity is fantastic and worth an awful lot but it's tempered by the fact that it's not actually part of their marketing strategy," he said. "Normally they would pay a fortune to get that kind of endorsement but obviously they're not paying anything so it's slightly out of their control and not necessarily on message."

Nevertheless it was still a huge endorsement for the brand, he said, particularly as Mr Obama's image was still "young, trendy and one of the people". This held true for the rest of the Obama family, he said.

Adidas, for example, is more than happy to claim style icon Michelle Obama as a fan. The soon-to-be First Lady, whose elegant fashion choices throughout the campaign led to comparisons with Jackie Kennedy, sported trainers made by the German firm when the couple attended a parent-teacher meeting on the Friday following the election. But, with a nod to her husband's long time supporter, the hat, of course, was one of Oprah's.

John Deacon, of Adidas, said the company was pleased that Mrs Obama had chosen its trainers, adding that it was "a reflection on the stylish sports brand that we are."

Mrs Obama, one of the world's most powerful women, was clearly aware of "the power of the three stripes", he added.

But it is not just the older Obamas who love their logos. Both Malia and Sasha, 10 and 7 respectively, have been snapped out and about wearing items from the outdoor clothing company Patagonia. Malia sported a purple quilted jacket and striped hat from the label when the family worked at a Chicago soup kitchen earlier this week, while Sasha wore a light green quilted coat when dropped off to school by her North Face-wearing father on the Monday following the election.

The soon-to-be First Family will have to be careful, especially after entering the White House, Mr Currie said. Celebrities in general, and politicians in particular, must make sure they do not overly favour any one brand, he added.

But Mr Obama's media team is a particularly shrewd operation - and the mutual benefit of the situation surely can't have escaped their attention. After all, nothing screams young, healthy and vigorous like head-to-toe sports brands. Perhaps John McCain missed a trick.

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