Rihanna has become "really focused" in keeping her body in shape, her fitness trainer has revealed.

The 23-year-old singer has undoubtedly one of the best bodies in the entertainment industry, and The Revolution's Harley Pasternak says she's working hard to keep it that way.

But although the Umbrella star is genetically blessed, she still needs to put in the time regardless of her busy schedule.

"She's got such a beautiful body," Harley told People magazine. "With someone like her, it's about the fine tuning."

When Rihanna is travelling she apparently tries to do at least three workouts a week, 25 minutes a session.

But when she is in a more stable location and can get into a routine, Harley says that she puts in more effort.

"She's been really focused and stepped it up," the celebrity trainer famed for his 5 Factor programme revealed.

He said that the Barbadian-born songstress has increased her workout sessions to five days a week and is now doing cardio 30 minutes a day rather than the 10 minutes that she used to do.

Rihanna's workouts consists of biking, cycling and fun exercises like jumping rope, jumping jacks and jogging on the spot.

"She can do those in a hotel room or backstage before a show," Harley said.

He added that Rihanna does try to eat a healthy diet consisting of five small meals a day but she does get "salty cravings" and uses Harley's high-protein 5 Factor snacks.

"She looks amazing," the fitness guru gushed. "She keeps getting better and better!"

Harley's team also train music stars Katy Perry and Lady Gaga.