Dive into a pool. The water should be at the height of your neck. Stand straight with your feet shoulder width apart. Your hands should be in a neutral position. Bend your right elbow around 90º and do an external rotation. Your elbow should be always in contact with your body.
In a fast movement, do an internal rotation while you exhale. Return to the starting position in a smooth movement while you inhale. Repeat the movement for the specified amount of repetitions and repeat with the other arm.TIPS: While your are doing the exercise, move only the arms, make sure you don't move any other part of your body. You can hold a towel between your elbow and torso to perform the exercise correctly. The exercise key is quality over quantity. The trick is to perform the exercise using proper form.