For those wishing to isolate the rear region of the shoulder, the bent over lateral raise is an ideal choice. By performing the raise with the arms perpendicular to the body, there is minimal latissimus dorsi recruitment, leaving the rear deltoid head to be the primary mover.
Involving the transverse abduction of the shoulder, the bent over raise primarily targets the rear deltoid, but also recruits the lateral head of the shoulder, as well as the infraspinatus, teres minor and the trapezius.
Although we discussing using dumbbells for the bent over lateral raise; cables and resistance bands also work very well and are preferred by some athletes.
The bent over cable raise requires the transverse abduction of the shoulder, therefore targeting the rear region of the shoulder, as well as the middle shoulder head and additional muscles of the upper back. It is mostly performed to isolate the rear head of the deltoids, and can be executed with either both arms simultaneously or with one arm at a time.
It is important to keep the working arm(s) perpendicular to the ground to ensure the shoulder goes through transverse abduction. If the upper arms begin to come towards the line of the torso during the exercise the more powerful latissimus dorsi (a.k.a. the "lats") muscle will take over.
The cable variation of the bent over raise is popular is many gyms, but it is worth noting it is possible to perform this exercise with dumbbells or with resistance bands.