07/31/2013 at 01:00 PM EDT
has one of Hollywood's most enviable bodies – and she credits it to an unconventional workout.
"I put on dance mixes and I really dance my brains out at home because I enjoy that," the actress told PEOPLE at the New York premiere of her upcoming film Lovelace
at the Museum of Modern Art on Tuesday.
"That saying – 'Dance like nobody is watching' – I do that. I dance like nobody's watching and I dance hard until I sweat and I think that that’s very good. It’s good for the mind and the body."
Along with her dedication to her dance moves, there's more that keeps Stone, 55, in phenomenal shape.
"I joined a gym," she said. "I used to just do Pilates. I had pilates in my house but I have found that since I've hit 50, that I've felt that I've needed more muscle tone and I started using more weights. So I joined a gym and I do weights. ... I really like it."
In the film, Stone plays Dorothy Boreman, Linda Lovelace's mother, opposite Amanda Seyfried
, the biopic about adult film star Linda Lovelace, opens Aug. 9.