Pectoralis Major
AnatomyDefinition
The pectoralis major is the main chest muscle, the one that gives volume and shape to the front of the torso. It's a broad, fan-shaped muscle that originates from the clavicle, the sternum, and the costal cartilages, and inserts on the humerus. Its primary function is adduction, flexion, and internal rotation of the arm.
The pectoralis major has two main portions that matter in the gym: the clavicular portion ('upper chest') and the sternocostal portion ('mid-lower chest'). The fibers of the clavicular portion run downward and laterally, so they respond best to incline presses and movements that bring the arm from below upward and toward the center. The sternocostal fibers run horizontally and upward, and they activate maximally with flat bench presses and flyes.
Every time you push something away from you or bring your arms toward the center of the body, the pectoralis major works. Barbell and dumbbell presses, cable flyes, chest press, push-ups: all are pec-dominant exercises. The bench angle changes the emphasis on the different portions. Incline at 30-45 degrees for the upper chest, flat for the sternocostal, decline for the lower portion. Cables and flyes let you work on horizontal adduction with a more constant resistance curve.
A well-developed pec requires work on both portions. If you only do flat bench, the clavicular portion will lag behind. If you only do incline, you'll lack thickness in the sternocostal area. Include at least one movement per portion in your training week and make sure to work through full ROM, taking the muscle into maximum stretch in the eccentric phase.
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