The trapezius muscle is a large, triangular muscle located in the upper back and neck. it originates on the occipital bone and the lower thoracic and upper lumbar vertebrae, and inserts on the clavicle, acromion, and scapula. the trapezius muscle is responsible for moving the scapula and supporting the weight of the arm. it is also used to turn the head and stabilize the shoulder blade. the trapezius muscle is often used in exercises that target the upper back, such as pull-ups, lat pull-downs, and shoulder shrugs.