Muscles of the Chest and Trunk – Chart

Chest and trunk    
 MuscleOrigin Insertion Action Notes 
IntercostalsInferior border of the rib aboveSuperior border of the rib belowExternal 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 majorSternal ½ of clavicle, sternum to 7th 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 minorThird, fourth and fifth ribsCoracoid process of scapulaTilts scapula forward, depresses and abducts scapula, Pulls shoulder forward when rhomboids are weak
DiaphragmSternal: inner part of ziphoid processCoastal- inner surface of lower 6 ribs

 

Lumbar- upper 2-3 lumbar vertebrae

Central tendonDraws central tendon down during inspiration, increases volume of thoracic cavity (increases diameters)Forms floor of thoracic cavity. 
Rectus abdominisCrest of the pubis, pubic symphysisCartilage of the 5th, 6th and 7th ribs and ziphoid processFlexes the vertebral columnSometimes origin and insertion are reversed
External obliquesLower eight ribs (5-12)Anterior part of iliac crest, abdominal aponeurosis to linea albaBilaterally- 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 obliquesLateral inguinal ligament, anterior iliac crest, thoracolumbar aponeurosisCartilage of lower 3-5 ribs (7-12), abdominal aponeurosis to linea albaBilaterally- 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 abdominisLateral inguinal ligament, anterior iliac crest, thoracolumbar fascia, cartilage of lower 6 ribs (7-12)Abdominal aponeurosis to linea albaCompresses abdominal contentsDeepest layer of abdominals: runs horizontally medialward
Quadratus lumborumPosterior iliac crest, iliolumbar ligamentLast rib, transverse processes of L1-L4Bilaterally- extends the spineUnilaterally- lateral flexion of lumbar spine

 

With spine fixed-elevates hip (hikes hip up).

Holds 12th 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 12th rib (vertical) Iliolumbar fibers run from the ilium to the transverse processes of L1-L4Lumbocostal fibers fun from the 12th rib to transverse processes of lumbar vertebrae