The band external rotation increases stability in the shoulder, more specifically the rotator cuff. This exercise may serve as a warm-up, prehabilitation, or rehabilitation exercise.
Attach a resistance band to a fixed object. Stand to the side of the object and grab the band with the hand that's farthest from the object, keeping your elbow bent 90-degrees and close to your ribs. Rest your forearm across your body.
Move your hand directly across your body and towards the outside of your shoulder while keeping your elbow stationary. Pause when you can go no further, then return to the starting position.
Keep your elbow in place and rotate at your shoulder.
Don't create an unnatural range of motion. You should be pain free.
Don't add extra, unnecessary tension. The goal is not to go heavy but instead to improve the range of motion.