Miss Mirren beat Elle Mapherson, Jennifer Lopez and Pippa Middleton to win the accolade.
Speaking to the newspaper, LA Fitness spokesman Tony Orme said: 'It's great to see the public celebrating bodies of all shapes and sizes, and proving that you really can look fabulous over 40 and 50.'
Forever young: Earlier Dame Helen enjoyed a game of hopscotch on the set of the Phil Spector biopic she is shooting
Miss Mirren plays Linda Kenney Baden in the Phil Spector movie, Spector's long-time lawyer and supporter, in the biopic, which stars Al Pacino as the former record producer who is now serving a prison sentence for the murder of actress Lana Clarkson.
The film is understood to be sympathetic to the former Beatles producer and claims he was wrongly jailed for murder.
Miss Mirren agreed to star in the movie despite being threatened with awards snubs and worse for refusing to pull out of the film.
Controversial: Miss Mirren relaxes with a cup of tea on set of the Phil Spector movie in which she plays Linda Kenney Baden, Spector's long-time lawyer and supporter