02/14/2012 AT 03:05 PM EST
As soon as she stepped onto the red carpet
at Sunday's Grammy Awards
, all eyes were on Rihanna
in her super sexy black Armani dress with its plunging neckline.
So how does the singer get such an attention-grabbing physique?
"She's got such a beautiful body naturally," says The Revolution
's Harley Pasternak, creator of the 5 Factor program
that has helped the pop star maintain her svelte figure. "With someone like her, it's about the fine tuning."
When she's on the road, the singer does her best to squeeze in at least three workouts a week, at least 25 minutes a day. But once settling in one location, Pasternak says, "She's been really focused and stepped it up," increasing her sessions to five days a week and bumping her cardio to a total of 30 minutes a day from 10."
Biking or cycling are part of her regular cardio routine, as well as exercises like jumping rope without a rope, stationary jogging and jumping jacks.
"She can do those in a hotel room or backstage before a show," Pasternak says.
And though she does her best to stick to a diet of five small meals a day, the "You Da One" singer still "gets salty cravings," he says, which she knocks out with Pasternak's high-protein, bean-based 5 Factor chips.
"They've been a big hit with our music and entertainment clients," says the trainer, whose team also works with other stars such as Katy Perry
and Lady Gaga
"She looks amazing," says Pasternak of Rihanna. "She keeps getting better and better!"