大圆肌, or the teres major, is a small muscle located in the upper back. It plays a crucial role in the movement of the shoulder joint, helping to rotate and adduct the arm. This muscle works in conjunction with other muscles, such as the latissimus dorsi, to facilitate various arm movements. The 大圆肌 originates from the lower part of the scapula and attaches to the upper part of the humerus. It is important for activities that involve pulling or lifting, making it essential for sports and daily tasks. Strengthening this muscle can improve overall shoulder stability and function.