This simple but extremely effective exercise works the back muscles that also help with posture. It is vital both that correct posture is maintained and that the weights used are not too heavy.

1 Sit facing the cable machine, either on the seat provided or on a stability ball, and adjust the weight stack as necessary. The cable pulley should be at around the height of your head when you are seated. Take an overhand grip on the cables and begin to pull back, keeping your elbows high and in line with your shoulders and hands. Maintain your "tall" posture and keep your abdominal muscles tight. 

2 Pull back until either your shoulderblades are touching or you have gone as far as your range of movement allows.

3 Retract and hold for a second before easing back to the start position, ensuring that your wrist, elbows, and shoulders are traveling in the same line. Repeat for the desired number of reps.