This exercise will help you define your upper back while giving you great posture.
Row On the Ball
Set Up: Seated upright on the ball, feet on the floor with a resistance band under the feet. Draw the abdominals inward and upward, keep the collar bones broad across the chest, and lengthen the crown of your head toward the ceiling. The arms are straight out in from of your holding that band. You can adjust the resistance by holding lower on the band to make it more challenging or holding the band closer to the top to make it easier.
Exercise: Holding the band,exhale as you spread the elbows wide and pull the band back. Inhale, return the arms forward. Keep lengthening in the spine and drawing the abdominals inward. Keep the chest wide but the neck soft. Feel the upper back muscles working. Repeat for 15 repetitions