Victoria Beckham's addiction to vertiginous heels doesn't just boost her height, she insists it increases her brain power too.

The 34-year-old, who is never knowingly seen in public without towering stilettos on her feet, says she also avoids the gym because she can't bear to be in trainers.

“I just can't concentrate in flats,” she explained during the second installment of her GMTV interview today.

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Boost: Victoria Beckham, arriving at the BBC in London today, says she 'can't concentrate' in flat shoes

“I could go to the gym if I wore flats, I'd love to go to the gym, but I just can't get my head around the footwear.”

Still, she says she occasionally comes back down to earth.

"When I'm at home with David and the kids I'm always in flip flops," she says.

Yesterday, the former Spice Girl addressed another element of her appearance - her permanently glum expression, saying it is nature, rather than a cranky disposition, that's to blame.

Victoria, who has plenty to smile about - handsome husband, healthy children and millions in the bank - says her stern appearance simply comes down to the structure of her face.

"When I see pictures I do sometimes think 'You miserable cow!' But I think it's just the way my face falls. If people like the way I look then great, and if they don't then fine."

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Unsporty Spice: Posh, pictured here throwing the first pitch at Dodger Stadium in wedge-heeled trainers, says she avoids the gym because she can't stand wearing sneakers

"You know it's a great place to bring up children. It's great for me and my career. You know, David – it's tough the football because it's completely different - but he went there for a reason, he's trying to change the face of soccer in America."

Of the recent Spice Girls reunion, she says: "I loved the whole social thing about being back with the girls, it was so much fun.

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Grin and bear it: Posh flashed a rare smile during her interview on GMTV today

But the star has promised to give up her music career once and for all, declaring: "I'm not going to sing anymore – I've hung my microphone up."

Posh, who has left her family in Los Angeles for her promotional visit to London for her dVb denim range, also addressed her friendship with Hollywood heavyweights Tom Cruise and Katie Holmes.

She said: "Do you know we go to lots of different things together and they're great and really normal. And people don't want to hear that, people want to hear that people are weird."