Holding a dumbbell in each hand, sit on the edge of a bench.
Position the dumbbells by your sides.
Keeping your elbow slightly bent and your back straight, exhale as you raise one dumbbell forward and upward in a semicircular motion until your arm is a little over horizontal.
Hold for a count of two.
Inhale as you reverse the motion and lower your arm to the starting position as you raise your opposite arm forward and upward.
Keep repeating, alternating the arm that you raise.
Comments and tips
Keep your body still. Only your arms should move. If you must sway back and forth to raise the dumbbells, they are too heavy.
You can use a hammer (neutral) grip, as in the illustration, or a pronated (overhand) grip. A neutral grip may be easier on your shoulder joints. You can also start off the raise using a neutral grip and, as your arm passes your leg, you can twist it so that it is pronated by the top of the movement. See the video.