What are the primary actions of the pectoralis major across the shoulder joint?

• A. Clavicular portion: flexion; Sternal portion: adduction and extension from a flexed position; both medially rotate.
• B. Clavicular: extension; Sternal: abduction; both laterally rotate.
• C. Clavicular: abduction; Sternal: flexion; both medially rotate.
• D. Clavicular: extension; Sternal: extension; both medially rotate.

Answer: (A)

The pectoralis major works across the shoulder to bring the arm toward the body and rotate it inward, with each head contributing differently. The clavicular portion sits up near the clavicle and primarily functions as a shoulder flexor, lifting the arm forward from the resting position. The sternocostal portion starts lower on the chest and, when the arm is already flexed, helps pull the arm back toward extension from that flexed position while still aiding adduction. Both parts work together to medially rotate the humerus. So the best description is that the clavicular part flexes the arm, the sternocostal part extends from a flexed position and both parts adduct and medially rotate. This aligns with the overall actions we expect from the pectoralis major and explains why other movements like abduction or lateral rotation aren’t primary actions of this muscle.