Rivera's trainer, Nichelle Hines, shared the same photo of the super-fit new mom, and revealed some insight on how the 29-year-old actress got back into fighting form.
"So proud of this gorgeous woman!!!" Hines wrote. "Her baby is 4 1/2 months old!!! She eats right, rides hard and trains hard. Hard work and dedication make anything possible. What'd you do this Monday???"