Janet Jackson: She's been accused of yo-yoing, but when Jackson's at the top of the yo-yo string, she rocks it. Her dancer moves and her rock-hard traps and obliques are a sight to behold. Her personal trainer, Tony Martinez, designed a complex assortment of workouts to fill Jackson's week, with a lot of emphasis on creative cardio, like boxing and baseball. Go deep? No other way. (John Shearer/WireImage.com)