1. Lie sideways on a flat bench. Hold a dumbbell in the lower arm and put the upper one on your waist or grasp the bench edge behind you.
2. Bend the elbow of the arm holding the dumbbell so that it creates a 90-degree angle between the shoulder and the forearm.
3. Now raise the upper arm (from the shoulder to the elbow) so that it is perpendicular to the torso and your forearm is perpendicular to the floor. The upper arm should be parallel to the floor and create a right angle with your torso. This will be your starting position.
4. Exhaling, externally rotate your forearm lifting the dumbbell forward as you maintain the right angle between the shoulder and the forearm. Continue this external rotation until the forearm is parallel to the floor. At the end of this movement, make a short pause.
5. Inhaling, slowly return your arm back to the starting position.
6. Repeat for the required amount of repetitions.
Precautions: There is no need to go heavy with this exercise. Too much weight can cause wrist injury.