The term 'BACK MUSCLES, FOR SHORT' is an abbreviation for two specific muscles located in the back. These muscles are the Latissimus Dorsi (LATS) and the Trapezius (TRAPS). The Latissimus Dorsi is a large, flat muscle that covers the lower and mid-back and is responsible for shoulder extension, adduction, and internal rotation. The Trapezius is a triangular shaped muscle that runs from the base of the skull to the lower thoracic vertebrae and is responsible for shoulder elevation, retraction, and rotation. Both of these muscles are important for providing stability and strength to the back and shoulders.