dumbbell lying external shoulder rotation

Lie on your side on a flat bench with your upper arm against your side and your elbow bent 90 degrees.

Hold a dumbbell in your hand with your palm facing down.

Keeping your upper arm against your side, slowly rotate your forearm upward as far as possible.

Pause for a moment at the top, then slowly lower your forearm back down to the starting position.

Repeat for the desired number of repetitions, then switch sides.