Do you know about a large diamond shaped muscle called the trapezius muscle? Its a large superficial muscle that extends from the neck to the midback area. Shoulder movement is one function of the trapezius. When you throw a ball, its the trapezius muscle that is working in addition to other muscles. The trapezius muscle also plays a role in neck pain and upper back pain. In more medical terminology, the trapezius muscle rotates, elevates, depresses and retracts the shoulder blade or scapula.
Read more about how to stretch the trapezius here:How to Get Upper Back and Neck Pain Relief by Stretching the Trapezius Muscle