"The girls have always been deeply competitive, especially Vic and Geri. So when she heard Geri has been working out like mad to get back into shape Victoria marched herself into the nearest exclusive gym and signed herself up,' the Daily Mail quoted a source, as saying.
"She hates working out and would rather fill her day with playing with the kids or shopping but Vic realises she has a bit of work to do before fitting into her skin tight catsuits and her little black dresses again," the source added.
It was only last week that Posh claimed that she doesn't like working out due to the whole sweaty thing.
"I really don't like the gym, in fact I can't stand it. Maybe it's the whole getting sweaty thing but it's just not me. I tried cycling in Spain but maybe my bum's too small as it just wasn't comfortable," Posh said.
"I want to get fit, though, so I'm exploring some different options. I like what I've heard about Pilates - just sitting in a room, stretching and breathing. Sounds much more civilised," she added.
However, after the mum of three saw pics of herself with cellulite on legs, she decided she has to do something to get back in shape.
The source added that now 33-year-old is in LA, she is under more pressure to look good.
"Vic was really unhappy after seeing photos of herself with cellulite on her legs last month and it gave her the final push to join a gym,' the source said.
"She takes a lot of pride in her appearance and knows it takes more than good clothes and good hair to pull off the perfect look... you have to have the perfect toned body too. And the pressures to look good in Hollywood are even more intense than at home in the UK," she added.