Muscles of the Chest and Upper Back (Male View)

[Continued from above] . . . and the abdomen below. The functions of its musculature system can be generally divided into the gross motor movements of the skeletal muscle anchored to the exterior of the ribs, and the work of the smooth muscles of the organs encircled within the ribs. Typically, the muscles of the upper back are treated separately.

Muscular organs fill the chest cavity, including the body's most important muscle, the cardiac muscle of the heart, pumping blood throughout the body. Below it, the diaphragm, a dome-shaped sheet of muscle that separates the chest from the abdomen, works with the muscles of the ribs and the skeletal structure of the torso to control positive and negative pressure within the chest cavity, enabling breathing. Smooth muscle activates the digestive system in the chest as well, with powerful waves of muscle contractions passing through the walls of the esophagus (which runs vertically throughout the thorax), to carry food and liquids from the throat to the stomach, itself lined with muscle.

On the outside of the ribs, skeletal muscles pull the body inward. Anchored at the breastbone (sternum) and the ribs, the pectoral and other muscles attach to the shoulder blade (scapula), vertebrae of the back and neck, the collarbones (clavicle), the abdomen, and the arms to collapse and pull the body inward and to thrust the shoulder forward as when pushing something, often antagonistically to the muscles of the back.

The upper back muscles include the deltoid, teres minor, teres major, latissimus dorsi and the trapezius muscles. Some of these muscles help move the shoulder and arm, but are located in the upper back. The deltoid is the triangular muscle of the shoulder that forms the rounded flesh of the outer part of the upper arm. It passes up and over the shoulder joint and attaches to the shoulder blade (scapula) and the collarbone (clavicle) as well as the upper arm bone (humerus).

There are two teres muscles. One is the teres minor, which rotates the arm laterally and assists in bringing it toward the body. As it draws the upper arm bone (humerus) up, it strengthens the shoulder joint. The teres major is a thick, flattened muscle that brings the arm toward the body and assists in extending it when the arm is in a flexed position. It is also an aid in rotating, but its function is just the opposite of the teres minor and other muscles in the rotator cuff.

The latissimus dorsi muscle in the back is attached to the pelvic girdle and vertebral column and the movable end is close to the midline of the humerus (upper arm bone). Usually, it functions to pull the arm toward the back as in rowing a boat or swimming, but during chinning exercises, the end attached to the humerus becomes the immovable end of the muscle, and the end attached to the pelvis and vertebral column moves.

The trapezius is a flat, triangular muscle that covers the back of the neck, shoulders and thorax. The upper and lower fibers are important to the orientation of the shoulder blade (scapula). The upper part, acting alone, elevates the shoulder and braces the shoulder girdle when a weight is carried. The lower part draws the scapula downward. When both of these muscles act together, the scapula can be brought toward the body and the head can draw directly backward.