Physical Therapy Assistant Practice Exam

During humeral flexion, which muscle mainly aids in protracting the scapula on the thorax?

1. Upper trapezius

2. Serratus anterior

3. Rhomboids

4. Pectoralis minor

The correct answer is: Serratus anterior

The serratus anterior is the primary muscle responsible for protracting the scapula during humeral flexion. This muscle originates from the surface of the first eight or nine ribs and inserts along the medial border of the scapula. Its contraction pulls the scapula forward and around the rib cage, which is essential for proper shoulder movement and stability. During activities that involve raising the arm, such as flexion, the scapula must be protracted to allow for a full range of motion. The serratus anterior works synergistically with other muscles to facilitate this movement, ensuring that the scapula follows the humerus appropriately. This action is crucial for maintaining shoulder girdle mechanics, preventing impingement, and supporting overall shoulder function. In contrast, while the upper trapezius is involved in elevating the scapula and is important for shoulder girdle movements, it does not primarily function to protract the scapula. The rhomboids are typically responsible for retracting the scapula, and the pectoralis minor assists in lowering and stabilizing the scapula but is not the main muscle responsible for its protraction during humeral flexion. Thus, the serratus anterior plays a critical role in this specific movement pattern.