According to several studies these two exercises are the best for targeting the following three rotator cuff muscles: Infraspinatus, Supraspinatus and Teres Minor (they result in the greatest EMG activity).
As you may already know, rotator cuff muscles are muscles that work in harmony to stabilize the arm in the shoulder blade cavity and allow the shoulder to function properly.
Side lying external rotation exercise for Infraspinatus and Teres Minor muscles:
While lying down on your side, hold a dumbbell in your hand so that the elbow is tucked in by your torso. Keeping your elbow tucked in by your torso at all times, move the dumbbell from its starting position by your stomach to right above the shoulder joint line.
Prone scaption with external rotation exercise for Supraspinatus muscle:
Although considered to be a highly advanced exercise for people returning to activity after shoulder injury, this is still considered the best exercise to activate the Supraspinatus muscle. Your physical therapist should let you know in advance if you are ready to perform this exercise.
Lay down on your stomach (either on an incline bench or a Swiss ball) and grab a dumbbell in your hand. Keeping your torso straight, move the arm diagonally up with straight elbow so that the thumb points up toward the ceiling.
I did not include a specific exercise for targeting the Subscapularis muscle which is the forth rotator cuff muscle since there is no concrete evidence as in regards to which exercise results in the greatest EMG activity of this muscle. Most literature will prescribe the standing internal rotation exercise to target this muscle.
As with all exercises given, the physical therapist’s clinical judgment should always dictate whether these exercises are beneficial to the client from the first place or whether they should be performed in different positions.
You can visit the Exercise Archive page to watch the exercises.