There’s a muscle group that doesn’t get enough credit: your transverse abdominus (TVA), says Aaron Guy, an accredited master trainer in Los Angeles. “It’s a very deep muscle that acts like a corset. When strong, it helps pull your abdomen in like a girdle,” he explains. (Spanx? Who needs Spanx?) Activate your TVA by incorporating compound movements into your routine, he says, like squat presses or deadlifts.