Infraspinatus and Teres minor (2 out of 4)
This propped external rotator targets the infraspinatus and teres minor.
Sit perpendicular to the barbell with arm flexed at 90 degrees at the elbow, and the forearm resting parallel on the barbell. Raise the dumbbell up until the forearm points up. Slowly lower the dumbbell and repeat, exercising both arms.
The posterior deltoid also aids in external rotation. Like the posterior deltoid, both the infraspinatus and teres minor also contribute to transverse extension of the shoulder, such as during a bent over row to the chest. They can be trained in this way besides isolating the external rotation action.