This is a very good back exercise that also isolates the upper back effectively when you retract the shoulderblades during the movement. The eccentric part of the movement also stretches the back muscles out.

1 Place your feet on the platform, keeping a slight bend in your knees and making your posture "tall". Grasp the handles and extend your back forward while keeping your shoulders slightly retracted, and then pull your elbows in and back toward the sides of your torso - the handles should come all the way in until it reaches your navel. 

2 Hold the position for a second before returning back out, keeping the movement under control: your arms returning to the extended position; your back going slightly forward; and with your knees slightly bent.

3 Repeat for the desired number of reps.