Set-up: Lying on your side, straighten your upper arm so that it is parallel to and resting on your upper body. Flex the elbow to 90 degrees so that the forearm is perpenidcular to your body pointing out in front of you.
Lift: Keeping your elbow fixed on your side, rotate your forearm from your front so that it is in line with your side. Return the weight to the starting position.
Emphasis: Do not use momentum and keep motion in the rest of the body to a minimum.
Repetitions: Perform all prescribed reps on one side, then on the other. This counts as one set.
Muscle Roles in external rotations - side lying, dumbbell