Which action can the clavicular head of pectoralis major perform?

Which action can the clavicular head of pectoralis major perform?

• A. Flexes the humerus
• B. Extends the humerus
• C. Abducts the humerus
• D. Rotates the scapula

Answer: (A)

The clavicular part of pectoralis major is positioned to pull the humerus forward from the chest. It originates from the medial half of the clavicle and inserts into the humerus, so its pull tends to flex the upper arm, especially from an extended position. The other portion of the muscle (the sternocostal part) helps extend the humerus from a flexed position and, together with both heads, aids adduction and medial rotation. Abduction is mainly done by deltoid and supraspinatus, and rotation of the scapula involves other scapulothoracic muscles, not this clavicular origin. So the clavicular head can flex the humerus.

The clavicular part of pectoralis major is positioned to pull the humerus forward from the chest. It originates from the medial half of the clavicle and inserts into the humerus, so its pull tends to flex the upper arm, especially from an extended position. The other portion of the muscle (the sternocostal part) helps extend the humerus from a flexed position and, together with both heads, aids adduction and medial rotation. Abduction is mainly done by deltoid and supraspinatus, and rotation of the scapula involves other scapulothoracic muscles, not this clavicular origin. So the clavicular head can flex the humerus.