Movement: Lying on your side with either a light dumbbell or light weight plate (emphasis on 'light' - the leverages in this exercise are very challenging), begin by extending the working arm perpendicular from the body, with the palm of the working hand pointing the same direction as your face. Maintaining a slight bend in the elbow, lower the arm past parallel to the floor, while rotating your arm so that your palm is now facing towards your feet. Lift the weight to the starting position under control without the use of momentum and repeat.
Repetitions: Perform all prescribed reps on one side, then on the other. This counts as one set.
Muscle Roles in side-lying shoulder horizontal abduction