Rihanna works out at 4am.

The 'California King Bed' hitmaker is so determined to stay in shape at all times, she adjusts her lifestyle in order to accommodate her fitness sessions, even getting up extra early to make sure she doesn't miss out on her daily physical activities.

Her trainer, Ary Nunez, said: "Rihanna trains as much as she can, whenever she can.

"This could be every day or three times a week. Her work schedule is extremely demanding, so thank goodness she's naturally a hard-working person.

"We make time and find time - whether it is at 4am or 9am."

According to her trainer, the 23-year-old beauty is even willing to work out while having her hair and make-up done.

Ary added: "We always squeeze it in."

While Rihanna works hard to maintain her toned physique, Ary believes she is naturally in good shape because it doesn't take long for her to look her best.

She told the new issue of Britain's Star magazine: "Rihanna has a gifted physique. She can become lean, get 'baby guns' [biceps] and firm up her core quickly.

"Her physique is the epitome of classic beauty, it's feminine, strong, agile, poetic and versatile."