Horizontal pulling exercises such as bent-over rows, dumbbell rows, seated rows, and machine rows mainly train the action of shoulder extension.

However, to strengthen horizontal shoulder abduction you need to add exercises like wide-grip rows, face pulls, dumbbell rear-delt flyes, or machine rear-delt flyes. The single-arm rear delt flye, shown in the video, also fits the bill.

Related:  The Isolation Exercise Checklist

Related:  The Cuban Press for Shoulder Health