Pectoralis Major – Anatomy Breakdown, Muscle by Muscle

Here we go!

Treadwell, DPT back with another Anatomy Breakdown – Muscle by Muscle.
Today we’re covering one of the most well-known and powerful muscles of the upper body—the Pectoralis Major. This is your classic “chest muscle,” a big player in pressing movements, athletic power, and functional strength. It’s a fan favorite in the gym, but also an essential stabilizer and mover in daily life.

Origin & Insertion

The Pectoralis Major has two heads:

• Clavicular head: Originates from the medial half of the clavicle.

• Sternocostal head: Originates from the sternum, upper six costal cartilages, and aponeurosis of the external oblique.

Both converge into a broad tendon inserting on the lateral lip of the intertubercular groove of the humerus.

Function

This is a powerhouse for adduction and medial rotation of the humerus.

• The clavicular head assists with shoulder flexion.

• The sternocostal head can help with shoulder extension (from a flexed position).
  Together, they drive pushing, pressing, and hugging motions—huge for athletes and gym-goers alike.

Innervation

• Clavicular head: Lateral pectoral nerve (C5–C7)

• Sternocostal head: Medial pectoral nerve (C8–T1)

Clinical & Research Insights

• Bench press injuries: Pec major ruptures are rare but usually occur with heavy lifting—especially during eccentric phases.

• Reconstruction: Surgical repair outcomes are generally favorable, restoring strength and function.

• Functional crossover: Its role in both athletic performance and posture makes it a key muscle for clinicians and trainers.