What is the primary function of the deltoid muscle?

The primary function of the deltoid muscle is to lift and turn the arm, which aligns with option C. The deltoid is a large, triangular muscle that caps the shoulder and is responsible for a wide range of movements at the shoulder joint. It is divided into three distinct parts: the anterior (front), lateral (middle), and posterior (rear) fibers.

The anterior fibers are involved in flexing and medially rotating the arm, the lateral fibers primarily function in abducting the arm (lifting it away from the body), and the posterior fibers assist in extending and laterally rotating the arm. This combination allows the deltoid to not only lift the arm upwards (abduction) but also to perform other movements such as rotation, making it essential for diverse arm movements in various activities such as lifting, throwing, and reaching.

In contrast, while the deltoid does play some role in stabilizing the shoulder joint, its primary function is focused on movement and mobility rather than stabilization alone. The other choices, which include solely flexing or extending the arm, do not encompass the full range of actions that the deltoid muscle supports. Thus, the answer accurately reflects the significance of the deltoid in facilitating the