The 32-year-old Grammy winner, who welcomed son Isaiah Michael in February, showed off her post-baby body in a photo shoot four months after giving birth, reported People Magazine.
Oprea said, a typical workout session for the singer included "a warm up and a cool down."
"Sometimes we'll go for a run with lots of hills, stop at a park to do some pull ups, push ups, step ups and other fun body weight stuff," she added.
Calling her client a "super motivated person with big goals," Oprea said the key was to "keep it fun and keep shocking the body."