As a Massage Therapist, a very common trigger to Postural Imbalance is the use of computers over a long period of time. Very often, the screen is too far away or too low, the keyboard or mouse is too far away when being used. Using the computer for hours at a time can leave the person leaning forward with the muscles of the upper back stretched, weakened and trying to hold you up. As you are leaning forward, the muscles at the base of your skull tighten to keep your head level with the horizon. This can cause headaches and reduced rotation of your neck and head.
Another aspect of this position in front of the computer is that your shoulders are turned inwards. This can weaken the Rotator Cuff Muscles that support the shoulder joint affecting the motion of the shoulder movement and can also impinge the nerves that travel down the arm causing muscle weakness and numbness.
Visit a Massage Therapist for information on bringing your body back into balance when working with a computer.