Lay down on a flat bench with your head at the very end of the bench. Hold a dumbbell around the end with both hands (palms facing up). Your arms should be pointed almost straight up, but tilted a little towards your head. While keeping your upper arms and elbows completely still, lower the dumbbell until it is behind your head. Do not let your elbows flare outward. Slowly lift the dumbbell back to the starting position where your elbows are locked or nearly locked. Repeat.