Reverse Flyes are great for both the rear shoulder and the upper back. By keeping your torso parallel to the floor, you can concentrate on the rear part of the shoulder as well as the 'posture' muscles of your upper back. Do it right: Using light dumbbells, sit on bench or ball (stand for more intensity) and lean over holding weights in front of legs. Raise arms out to the side to shoulder height, keeping elbows in a fixed (slightly bent) position. Lower and repeat for 2-3 sets of 10-12 repetitions.