External Intercostals

Origin, Insertion, Action, Innervation

Origin: Inferior border of the rib above (from the tubercle of the rib to the costochondral junction)
Insertion: Superior border of the rib below
Action:
Primary: Elevation of the ribs during inspiration — increases the anteroposterior and lateral dimensions of the thorax (pump-handle and bucket-handle motions)
Innervation: Intercostal nerves (ventral rami of T1–T11)

Palpation Guide

Client position: Supine or side-lying with the arm abducted to expose the lateral rib cage.
Landmark sequence:

Locate any intercostal space on the lateral or anterior rib cage — the space between two adjacent ribs.
Place your fingertip in the intercostal space. The external intercostal fibers run obliquely downward and forward (same direction as the external oblique — "hands in pockets").
The external intercostals are most palpable on the lateral rib cage, where they are not covered by other muscles. Anteriorly, they give way to the external intercostal membrane (no muscle fibers between the costochondral junctions and the sternum).
Posteriorly, the external intercostals are covered by the erector spinae and other posterior muscles.

Tissue feel: Thin, sheet-like muscles between the ribs. When relaxed, the intercostal space feels soft and yielding. When hypertonic or in spasm, the space feels tight, restricted, and tender. Individual muscle fibers are not independently palpable — you feel the intercostal tissue as a unit.
Confirmation test: Ask the client to take a deep breath. The external intercostals contract during inspiration, and you may feel the intercostal space become taut and the ribs elevate under your fingers.
Common errors:
Confusing external intercostals with internal intercostals — they occupy the same spaces but have opposite fiber directions. Differentiation by palpation is not clinically feasible; they are assessed functionally (inspiration vs. expiration).
Pressing too deeply between the ribs — the pleura and lung tissue are just deep to the intercostal muscles. Sustained deep penetration between the ribs is uncomfortable and unnecessary.

Trigger Point Referral

Common TrP locations: TrPs are found in the intercostal spaces, particularly along the lateral rib cage between the mid-axillary line and the anterior axillary line.
Referral pattern: Refers along the intercostal space in a band-like pattern, following the rib from posterior to anterior. The pattern wraps around the trunk at the level of the affected rib.
Clinical significance: The band-like referral pattern mimics intercostal neuralgia, herpes zoster (shingles) prodrome, or referred visceral pain (especially left-sided intercostal pain mimicking cardiac pain). Always rule out cardiac and visceral causes before attributing chest wall pain to intercostal TrPs.

Trigger point referral diagram — coming soon

Image coming soon. For visual reference, see [External Intercostals at TriggerPoints.net](http://www.triggerpoints.net/muscle/external-intercostals).

Clinical Notes

Common conditions:

Intercostal muscle strain — acute strain from coughing, sneezing, or rotational trunk movements. Produces sharp, localized pain that worsens with breathing, coughing, and trunk rotation. Distinguished from rib fracture by the absence of point tenderness on the rib itself (the pain is between the ribs, not on them).
Intercostal neuralgia — irritation of the intercostal nerve produces sharp, burning pain along the dermatome of the affected rib level. Can be caused by thoracic disc pathology, herpes zoster, or compression by hypertonic intercostal muscles.
Involved in thoracic mobility restriction — hypertonic intercostals limit rib cage expansion and contribute to reduced thoracic rotation and breathing capacity.
Post-thoracotomy or post-mastectomy scarring can involve the intercostal muscles, producing chronic chest wall pain and restricted breathing.

What you'll typically find:

In clients with restricted thoracic mobility or shallow breathing, specific intercostal spaces are often tender and restricted. The lateral rib cage (mid-axillary line) is the most common area of restriction.
Post-surgical clients (thoracotomy, breast surgery, cardiac surgery) frequently have intercostal adhesions and tenderness that persist for months after the procedure.

Treatment effects:

Responds to gentle sustained pressure in the intercostal space, parallel to the rib. Cross-fiber techniques (perpendicular to the ribs) can release hypertonic intercostal fibers.
Post-treatment, clients typically report easier, deeper breathing and reduced chest wall tightness. Thoracic rotation may improve.
In post-surgical clients, scar mobilization of the intercostal area (after appropriate healing time — typically 6–8 weeks) can significantly reduce chronic chest wall pain.

Cautions:

Left-sided chest wall pain must always be evaluated for cardiac causes before attributing it to intercostal muscles. If the client has left-sided chest pain with exertional worsening, shortness of breath, radiation to the arm or jaw, or associated nausea/sweating, refer for emergency medical evaluation. Only after cardiac causes are ruled out should musculoskeletal treatment proceed.
The intercostal neurovascular bundle (vein, artery, nerve) runs along the inferior border of each rib in the costal groove. Avoid pressure directly on the inferior rib border — work in the center of the intercostal space.
Pneumothorax risk — do not use acupuncture needles or deep penetrating instruments in the intercostal spaces. Manual therapy pressure is safe because the therapist's fingers are too broad to penetrate between the ribs into the pleural space, but awareness of the underlying lung tissue is important.

Clinical pearl:

When a client presents with chest wall pain that wraps around from the back to the front in a band pattern, think three things: (1) intercostal TrP/strain (musculoskeletal — most common), (2) thoracic facet or costovertebral joint dysfunction (articular), (3) herpes zoster prodrome (viral — ask about tingling, burning quality, and recent immune compromise). The treatment approach differs completely depending on the cause, so differential reasoning matters here.

Assessment

Manual muscle testing:

The intercostals are not individually strength-tested. Assessment focuses on rib cage expansion and breathing mechanics.

Stretch test:

Lateral trunk flexion with arm overhead: Side-bend away from the tested side with the ipsilateral arm overhead. This opens the intercostal spaces on the stretched side. Restricted expansion or pain suggests intercostal shortening or pathology.

Related special orthopedic tests:

Rib spring test — anteroposterior compression of the rib cage; pain suggests rib fracture or costovertebral joint dysfunction
Thoracic expansion measurement — < 3 cm expansion suggests restricted intercostal/diaphragmatic function

Muscle Groups

Primary respiratory muscles (functional):

anatomy/muscles/diaphragm (primary inspiratory)
External intercostals (this article — accessory inspiratory)
anatomy/muscles/internal-intercostals (expiratory)

Intercostal muscles (anatomical):

External intercostals (this article)
anatomy/muscles/internal-intercostals
Innermost intercostals (deepest layer)

Related Muscles

Synergists for inspiration:

anatomy/muscles/diaphragm — primary muscle of inspiration
Scalenes — elevate ribs 1–2
anatomy/muscles/serratus-posterior-superior — elevates ribs 2–5

Antagonist:

anatomy/muscles/internal-intercostals — depress the ribs during forced expiration

Key Takeaways

External intercostals elevate the ribs during inspiration — hypertonic intercostals restrict rib expansion and contribute to shallow breathing and thoracic stiffness.
Left-sided chest wall pain must always be evaluated for cardiac causes before treating musculoskeletally — this is a non-negotiable clinical rule.
The intercostal neurovascular bundle runs along the inferior rib border — work in the center of the intercostal space, not along the bottom of the rib.