Shoulder exercises work the deltoid muscle, the large muscle forming the rounded contour of the shoulder. The deltoid muscle is made up of three primary areas: the anterior (front) deltoid, the lateral deltoid, and the posterior (rear) deltoid. Certain shoulder exercises known as often known as trapezius or trap exercises work the trapezius mucle, the large triangular muscle on the upper back that connects the neck to the shoulders. All trap-specific exercises involve a simple upward rowing or shrugging motion. Below is a list of shoulder exercises by motion and area of focus.