Muscles of the Chest and Trunk – Chart

Chest and trunk
Muscle	Origin	Insertion	Action	Notes
Intercostals	Inferior border of the rib above	Superior border of the rib below	External Intercostals: draw the ventral part of the ribs upward, increasing thoracic cavity space Internal Intercostals: draw the ventral part of the ribs downward, decreasing the space of the thoracic cavity	Stabilize the rib cage and assist in respiration. Meat of spare ribs.
Pectoralis major	Sternal ½ of clavicle, sternum to 7^th rib, aponeurosis of external oblique muscle.	Crest of greater tubercle of humerus: Lateral lip of bicipital grove.	Clavicular (upper) fibers- flexion of humerusSternocostal (middle and lower) fibers- extension of humerus returning from flexion Adduction, medial rotation	Forms the anterior wall of axilla. Upper and lower fibers are work in opposite actions making it an antagonist to itself. Triggerpoints may cause pain, swelling and congestion of lymphatic fluids in breast tissue.
Pectoralis minor	Third, fourth and fifth ribs	Coracoid process of scapula	Tilts scapula forward, depresses and abducts scapula,	Pulls shoulder forward when rhomboids are weak
Diaphragm	Sternal: inner part of ziphoid processCoastal- inner surface of lower 6 ribs Lumbar- upper 2-3 lumbar vertebrae	Central tendon	Draws central tendon down during inspiration, increases volume of thoracic cavity (increases diameters)	Forms floor of thoracic cavity.
Rectus abdominis	Crest of the pubis, pubic symphysis	Cartilage of the 5^th, 6^th and 7^th ribs and ziphoid process	Flexes the vertebral column	Sometimes origin and insertion are reversed
External obliques	Lower eight ribs (5-12)	Anterior part of iliac crest, abdominal aponeurosis to linea alba	Bilaterally- flexes thorax and compresses abdominal contents Unilaterally- laterally flexes spine and rotates spine to opposite side	Interdigitates with serratus anterior. Place hands on hips as if you were reaching into pants pockets to follow directions of fibers (obliquely downward and medialward)
Internal obliques	Lateral inguinal ligament, anterior iliac crest, thoracolumbar aponeurosis	Cartilage of lower 3-5 ribs (7-12), abdominal aponeurosis to linea alba	Bilaterally- flexes the thorax, compresses abdominal contents Unilaterally- laterally flexes spine and rotates trunk to same side	Place hands over abdomen with fingertips on the anterior-superior iliac spine, your fingertips will follow the direction of the fibers (obliquely upward and medialward)
Transverse abdominis	Lateral inguinal ligament, anterior iliac crest, thoracolumbar fascia, cartilage of lower 6 ribs (7-12)	Abdominal aponeurosis to linea alba	Compresses abdominal contents	Deepest layer of abdominals: runs horizontally medialward
Quadratus lumborum	Posterior iliac crest, iliolumbar ligament	Last rib, transverse processes of L1-L4	Bilaterally- extends the spineUnilaterally- lateral flexion of lumbar spine With spine fixed-elevates hip (hikes hip up). Holds 12^th rib against the pull of the diaphragm Accessory breathing muscle. Spinal stabilizer	Composed of three groups of fibers: Iliocostal fibers run from medial upper crest of ilium and iliolumbar ligament upward to 12^th rib (vertical) Iliolumbar fibers run from the ilium to the transverse processes of L1-L4Lumbocostal fibers fun from the 12^th rib to transverse processes of lumbar vertebrae