With your feet hip width apart, hinge forward from your waist, so your torso is leaning over slightly (no more than a 45-degree angle from a standing position). Your knees should be slightly bent.
Hold a dumbbell in each hand, your palms facing in toward your body. From here, bend your right elbow, and pull your right dumbbell up and back toward your spine, driving from your elbow and keeping it tight against the right side of your body. At the top of the move, the dumbbell will be next to your rib cage.
Lower your right arm back to the starting position, then repeat on the left side. Continue this pattern for 20 reps, alternating arms as you work.