Lesson 10: Pectoralis Major, Latissimus Dorsi, and Teres Major

This course describes the pectoralis major, latissimus dorsi, and teres major, which contribute to motion of the humerus at the shoulder joint (glenohumeral joint).

• The latissimus dorsi muscle is the largest muscle of the upper body. The latissimus dorsi tendon inserts under the deltoid on the humerus (upper arm bone), although there may be a small additional insertion on the scapula (shoulder blade), and the muscle originates from the lumbar vertebra and pelvis. This muscle is the prime mover of shoulder extension and adduction, and it may contribute to shoulder internal rotation (medial rotation), as well as lumbar extension, lumbar rotation, and lumbar lateral flexion. Interesting facts, the latissimus dorsi is the largest skeletal muscle of the upper body, may be biased toward type II muscle fibers, and a flap of this muscle is often used in surgical procedures.
• The teres major muscle is located inferior to the teres minor muscle (a rotator cuff muscle), has a tendon that inserts on the upper arm near the insertion of the latissimus dorsi and subscapularis, and the muscle originates on the inferior angle of the scapula (shoulder blade). This muscle will perform the same joint actions at the shoulder as the latissimus dorsi, including shoulder joint extension, adduction and internal rotation (medial rotation). Interesting facts, over-activity of this muscle may be addressed with physical therapy for the treatment of shoulder impingement syndrome, and a teres major steak from a cow may be used as “mock” beef tenderloin.
• The pectoralis major muscle has a large muscle belly on the anterior surface of the chest wall, superficial to the pectoralis minor, and is comprised of a sternocostal head and a clavicular head. The tendon inserts under the deltoid on the upper arm, near the insertion of the latissimus dorsi and rotator cuff muscles. This muscle is the prime mover of shoulder horizontal adduction, and will contribute to adduction, flexion, and internal rotation. Interesting facts, pectoralis major injuries including a partially torn muscle or partial tendon tear, are rarely surgically repaired. Surgical repair is generally reserved for a complete rupture.

Sports medicine professionals (personal trainers, fitness instructors, physical therapists, massage therapists, chiropractors, occupational therapists, athletic trainers, etc.) must be aware of these major muscles of the shoulder for detailed analysis of human movement, and the development of sophisticated exercise programs and therapeutic (rehabilitation) interventions. Further, this course is essential knowledge for future courses discussing more detailed anatomy like neural innervations (e.g. the thoracodorsal nerve), synergistic function with other muscles of the shoulder and scapula (e.g. deltoids, serratus anterior, trapezius muscle, etc.), role in injury (e.g. shoulder pain, shoulder impingement syndrome, muscle flap procedures, hypertonic muscle fibers, muscle strain, pectoralis major tear), and sports performance (e.g. throwing, shooting, punching, lifting).

For more advanced anatomy check out our integrated functional anatomy courses:

• Pectoralis Major
• Latissimus Dorsi
• Teres Major

Caption: The lats, covering most of the thoracic and lumbar spine