The single-arm bent-over rear delt fly is a popular upper-body exercise that targets the muscles on the back of the shoulder joint, specifically the rear head of the deltoid. Since pressing movements build the front and (to a lesser degree) side deltoid heads, this move is often done to promote balanced shoulder development. It is usually performed for high reps, such as 10-15 reps per set or more, as part of a shoulder or upper-body workout.
Promotes aesthetically and functionally balanced shoulders
Builds muscle in the rear delts and upper back
Single-arm sets allow you to focus on one shoulder at a time