Which muscle is primarily involved in shoulder flexion?

The anterior deltoid is primarily involved in shoulder flexion due to its anatomical position and function. This muscle is located on the front part of the shoulder and is specifically designed to initiate the movement of raising the arm forward and upward, which defines shoulder flexion. When the anterior deltoid contracts, it pulls the humerus upwards and forwards, contributing significantly to the shoulder flexion movement.

In contrast, the latissimus dorsi is mainly responsible for shoulder extension, adduction, and internal rotation. The supraspinatus plays a significant role in shoulder abduction and stabilization of the shoulder joint, while the infraspinatus is primarily involved in external rotation of the shoulder. Therefore, while these other muscles have important roles in shoulder mechanics, they are not the primary movers for shoulder flexion like the anterior deltoid.