The right ab exercise can make all the difference when it comes to creating a slim waist and hourglass silhouette. That’s according to two-time Ms. Figure Olympia Erin Stern, who said you can “lose up to an inch or two off your waist” with one specific move: the vacuum crunch . It’s a cable ab exercise that combines two rock-solid core movements. We’re going to explain how to do it and look at some science to see if Stern is on the money. The Best Ab Exercise for a Slim Waist: Vacuum Crunch According to Stern , certain core training moves can improve your posture and waistline simultaneously. The vacuum crunch combines two ab-training moves: a standard cable crunch and the stomach vacuum technique. [Related: Best Pre-Workout Supplements ] To win the Ms. Figure Olympia, the rules stipulate all contestants must have a pronounced v-taper, which has two parts: A broad upper body and a slim, snug waistline. Stern won the Figure Olympia twice , so we’re inclined to take her...