The back is crisscrossed by broad bands of muscle. The widest muscles in the back are the trapezius, the levator scapula, the rhomboids, and the latissimus dorsi. The muscles in the lower back provide support for your upright posture. The muscles at the top of the back move the shoulders and arms, and help you breathe. Those in the central group steady the spine and enable you to bend forward and backward and to twist from side to side. The deeper muscles form an overlapping sheet that joins this central region to the phalanges on the scapula (shoulder blade) and pelvis (hips). Other muscles link these bones to the arms and legs. Many of the muscles that give strength to the back of the upper torso are near the surface of the skin. A deep layer of muscles, some interwoven with the ribs and others linked to the spine, provide flexibility and added stability to the back.
The deltoid muscle is a thick triangular muscle which cups the shoulder joint. It is attached to the clavicle (collar bone) and scapula (shoulder blade) at its upper end, and to the shaft of the humerus (upper arm bone) at its lower end. The muscle is divided into three portions: an anterior (clavicular) portion, and acrominal (middle) portion, and a posterior portion. The posterior portion is located on the back of the shoulder. Almost any movement of your shoulder and upper arm involves the deltoid muscle. The anterior portion is used to raise the arm from the body and to lower it again. The acrominal portion is a powerful abductor and the posterior portion is used to move the arm backward.
The erector spinae, or sacrospinalis, consists of several combined muscles which form a thick, elongated muscle mass that runs from the top of the neck to the small of the back. The overlapping column of long, slim muscles stretch alongside to the rear of the vertebrae. These muscles link the vertebrae, helping you to stand upright and enabling you to bend and twist.
The external oblique is a large, thin sheet of overlapping muscle that runs along the side of the torso and partly on the front from the lower ribs to the rectus, the pubis bone, and the iliac crest of the hip. The muscle is divided into two portions; and upper thoracic portion and a lower flank portion. The thoracic portion is located along the rib cage. The individual ribs can be seen beneath this muscle when it is relaxed. The lower flank portion is located along the side of the abdomen between the rib cage and the pelvis. Most of this muscle is concealed by fat. The two portions meet at the waist. This muscle assists the rectus abdominis muscle in flexing (bending) the spine when the trunk twists or turns. It also supports the abdominal organ tissue.
We sit on the most powerful and largest muscle in our body, the gluteus maximus. It is a thick, fleshy, quadrilateral muscle that forms the major volume of the buttock. The muscle descends downward and outward from its origin and wraps around the outer back corner of the pelvis. It connects the ilium, sacrum, and coccyx to the femur by tissues of the thigh. The gluteus maximus consists of coarse muscle fibers that powerfully extend (straightens) the thigh at the hip joint and moves it away from the body, as when walking or running. It is also used to raise the body from a sitting position.
The gluteus medius is a wide, fan-shaped muscle that tapers into a strong flattened tendon at its insertion on the femur (thigh bone). It runs from the outer portion of the ilium (pelvis), up to the crest of the ilium. The gluteus medius is partly covered by the gluteus maximus. You can feel the crest of the gluteus medius through the skin. It moves the thigh outward and rotates it, as when walking or running. It keeps the torso upright during walking when one foot is touching the ground and the other is not touching the ground. The gluteus minimus lies just beneath the gluteus medius and works with it.
The infraspinatus muscle is attached along the broad inner edge of the scapula (shoulder blade). It narrows into a strong tendon that joins firmly to the top of the humerus (upper arm bone). The infraspinatus muscle sits on the back of the shoulder blade below the spine and under the deltoid muscle. It works with the supraspinatus to help lift and twist the upper arm. These two muscles also help support and protect the shoulder joint by keeping the head of the humerus in place.
The base of this triangular muscle is attached along the lumbar and lower half of the thoracic vertebrae (spine), the lower ribs, and even the hip bones far below. The latissimus dorsi is a wide, flat muscle located on the lower half of the back. The muscle fibers at its tip insert under the scapula (shoulder blade) and join to the humerus (upper arm bone) in the shoulder. This muscle gives your arms motion. It is used when swimming or when you swing your arms back when jogging. It is also used to reach up to grab something above your head.
The levator scapula lies along the back and side part of the neck. It originates deep in the side of the neck near the base of the skull, passes down and back and inserts in the scapula (shoulder blade). As the name implies, this muscle is the "shoulder blade lifter". This muscle tenses up, becoming hard and stiff, when you carry a weight on your shoulder.
The rhomboideus major and the rhomboideus minor form a flat, quadrilateral muscle of the upper back that lie under the trapezius. The muscles extend from the spine to the edge of the scapula (shoulder blade). They are barely separable as two muscles. These muscles assist in rotating the scapula and supporting the head. When you sneeze, the shoulder, back and abdominal muscles contract quickly to force air out of the nasal passages, while the rhombodeus major and minor muscles hold your head and neck steady.
The semispinalis capitis is a deep muscle on the back of the neck. It originates from the spine (7th cervical down to the 6th or 7th thoracic vertebrae) and inserts into the elongated area at the base of the skull. It is a deep muscle that lies under the trapezius muscle. Both the trapezius and the semispinalis capitis create the muscular column on the back of the neck. The semispinalis capitis muscle extends the head and rotates it so the face is directed to the opposite side.
The serratus anterior (serratus magnus) is a large quadrilateral muscle that curves along the rib cage. The muscle is divided into several bundles, each of which extends along the side and upper border of each rib. The muscle is divided into two portions, and upper and lower portion. The upper portion lies along the upper side of the rib cage and the armpit. The lower portion consists of five or six pointed digitations which create a fan-shaped mass extending from the scapula (shoulder blade). This muscle is used everytime you reach out or push forward with your arms. It also helps raise the shoulder joint when lifting your arm above your head.
The serratus posterior superior and inferior muscles lie deep on the front part of the neck. The serratus posterior superior is a thin, flat, quadrilateral muscle that extends from the neck to the third, fourth, and fifth ribs. The serratus posterior inferior is broader than the serratus posterior superior and extends to the four lower ribs. Both muscles are respiratory muscle. The serratus posterior superior elevates the ribs as you inhale and the serratus posterior inferior pulls the ribs down and back to exhale.
The splenius capitis is a broad, sheet-like muscle located on the back of the neck. It originates from the cervical and thoracic vertebrae and inserts in the base of the skull. This muscle is used to turn the head.
The sternocleidomastoid muscle is located in the neck. It is a thin, broad muscle that narrows at the center. It originates from two heads, one from the sternum (breastbone) and one from the clavicle (collar bone), and runs upward, inserting into the mastoid (the temporal bone behind the ear). This muscle is used to tilt the head from side to side.
The supraspinatus muscle is attached along the broad inner edge of the scapula (shoulder blade). It narrows into a strong tendon that joins firmly to the top of the humerus (upper arm bone). The supraspinatus muscle runs along the top of the shoulder under the trapezius muscle. This muscle works with the infraspinatus muscle to help lift and twist the upper arm. They also help to protect the shoulder joint by keeping the head of the humerus bone in place.
The teres major is a short and thick, somewhat flattened muscle that extends from the scapula (shoulder blade) to the humerus (upper arm bone). This muscle creates part of the posterior wall of the armpit and helps adduct the arm. It also rotates the arm medially behind the back. The teres major tenses when the arm lies next to the body. When the arm is extended the teres major is stretched, becoming elongated and thinner.
The teres minor is a small, elongated muscle that runs from the scapula (shoulder blade) to the humerus (upper arm bone). It inserts in the humerus by a flat, thick tendon. It laterally rotates the arm and helps stabilize the shoulder joint by holding the head of the humerus in its socket.
The trapezius is one of the biggest shoulder muscles and the most superficial muscle on the back of the neck and upper trunk. It is a broad, flat triangular muscle that lies just below the skin, covering the upper back part of the neck and shoulders. It links the neck with the spine (dorsal vertebrae), ribs, and shoulder bones (scapula). This muscle is used to turn and tilt the head, raise and twist the arms, and to shrug or steady the shoulders. The trapezius is a postural muscle as well as an active mover.
Deep back muscles
The small muscles deep in the back play an important role in controlling the joints between the vertebrae of the spine. They steady the spinal column so that the long muscles of the back can use the spine as a lever when bending and twisting the torso. These muscles are therefore, also important to posture.
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