Set-up: Either lying prone on an elevated bench or bending over at your hips and stabilizing your off hand on a bench, grasp a light dumbbell in one hand.
Lift: Keeping the arm straight, pull the shoulder blade tightly back into place. Hold briefly and repeat.
Repetitions: Perform all prescribed reps on one side, then on the other. This counts as one set.
Instructions and effects for the Dumbbell Retraction exercise 
