The chest contains several distinct muscle groups that perform numerous functions. These muscles form a structural network across the upper front of the torso, providing mobility for the upper limbs and stability for the shoulder girdle. They also support the mechanics of breathing and offer protection for the internal organs housed within the rib cage.
The Primary Pectoral Muscles
The most prominent muscles of the anterior chest wall are the pectorals, or “pecs,” divided into two main structures. The Pectoralis Major is the larger, fan-shaped muscle that lies superficially, creating the bulk of the chest mass. It originates from the collarbone, sternum, and upper ribs, connecting broadly across the chest.
Deep to the Major lies the Pectoralis Minor, a smaller, triangular structure. This muscle originates on the third, fourth, and fifth ribs and attaches to the coracoid process, a bony projection on the shoulder blade. The Pectoralis Minor does not attach directly to the upper arm bone. Both muscles work together, but their distinct attachments give them slightly different roles in shoulder and arm movement.
How the Chest Muscles Move Your Arms
The Pectoralis Major is the primary engine for several arm movements, connecting the chest to the humerus. Its main action is horizontal adduction, which is the motion of bringing the arm across the body’s midline, such as when hugging or throwing a frisbee. It also contributes to the medial rotation of the arm at the shoulder joint.
The Pectoralis Minor acts mainly to stabilize the shoulder blade, keeping it pressed firmly against the rib cage. This stability is necessary for the larger arm movements to occur efficiently.
Beyond the Pecs Supporting Muscle Groups
The chest cavity houses other muscle groups that perform functions necessary for life. The intercostal muscles are thin sheets layered between the ribs. These groups are instrumental in respiration, responsible for expanding and contracting the volume of the thoracic cavity during inhalation and exhalation.
Another muscle group is the Serratus Anterior, located on the side of the chest, originating on the outer surface of the upper eight or nine ribs. It is often called the “boxer’s muscle” because its main action is the protraction of the scapula, pulling the shoulder blade forward around the rib cage. When the shoulder is fixed, the Serratus Anterior assists the intercostals by lifting the ribs, aiding in deep inspiration.
Strengthening and Maintaining Chest Muscle Health
Training the chest muscles promotes upper body strength and helps maintain good posture by supporting shoulder alignment. Common exercises effectively target these muscles, including the push-up, which uses body weight to strengthen the entire group. Targeted resistance training, such as the bench press or cable flyes, activates the Pectoralis Major fibers.
Maintaining a balanced training regimen is important to prevent muscle imbalances that can lead to poor posture or injury. Overly tight chest muscles can pull the shoulders forward, while a sudden strain can cause pain during pushing motions. Including exercises that strengthen the upper back helps counteract this forward pull and keeps the shoulder joint stable and healthy.