The middle fibers of the deltoid muscle are primarily responsible for which movement of the arm?

• A. Abduction of the arm
• B. Extension of the arm
• C. Medial rotation of the arm
• D. Flexion of the arm

Answer: (A)

Verified step by step guidance

1. Step 1: Begin by identifying the anatomical location and function of the deltoid muscle. The deltoid is a triangular-shaped muscle located on the shoulder, and it is divided into three parts: anterior (front), middle, and posterior (back) fibers.
2. Step 2: Focus on the middle fibers of the deltoid muscle. These fibers originate from the acromion of the scapula and insert onto the deltoid tuberosity of the humerus. Their primary function is to move the arm away from the body, a movement known as abduction.
3. Step 3: Understand the term 'abduction.' Abduction refers to the movement of a limb away from the midline of the body. For the arm, this means lifting it sideways away from the torso.
4. Step 4: Compare the other options provided in the question. Extension refers to moving the arm backward, medial rotation involves rotating the arm toward the midline, and flexion refers to moving the arm forward. None of these movements are primarily performed by the middle fibers of the deltoid.
5. Step 5: Conclude that the middle fibers of the deltoid muscle are primarily responsible for abduction of the arm, as this is their main function based on their anatomical structure and location.