| 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 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 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 5th, 6th and 7th 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 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 |