Muscle Group: 

Lay face down on a flat bench high enough for your arms to hang down to the floor.

Place a dumbbell at your side.

Your other hand not grasping the dumbbell can be on the floor stabilising your movements.

Grasp the dumbbell in your hand and raise your upper arm to shoulder height.

Keep your arm straight and perpendicular to your chest with a slight bend in the elbow.

In a slow controlled manner lower your arm to starting position.