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Internal Intercostals

Muscles

The internal intercostals are eleven pairs of muscles occupying the intercostal spaces deep to the external intercostals, with fibers running obliquely downward and backward — opposite to the external intercostals. They are the primary accessory muscles of forced expiration, depressing the ribs to compress the thoracic cage, and are clinically indistinguishable from the external intercostals on palpation.

Origin, Insertion, Action, Innervation

  • Origin: Superior border of the rib below (from the sternum to the rib angle)
  • Insertion: Inferior border of the rib above (costal groove area)
  • Action:
  • Primary: Depression of the ribs during forced expiration — decreases the thoracic volume (active during coughing, sneezing, and forced breathing)
  • Note: Quiet expiration is passive (elastic recoil of the lungs and chest wall); internal intercostals are recruited only during forced or active expiration
  • Innervation: Intercostal nerves (ventral rami of T1–T11)

Palpation Guide

  • Client position: Supine or side-lying with the arm abducted.
  • Landmark sequence:
  1. The internal intercostals lie deep to the external intercostals in the same intercostal spaces. They cannot be palpated as a separate layer.
  2. Their fiber direction is opposite to the externals — downward and backward (perpendicular to "hands in pockets"). This anatomical fact is important for understanding their function but does not change the palpation technique.
  3. Palpation of the intercostal spaces assesses the combined intercostal muscle layers. Anteriorly (between the costochondral junctions and the sternum), only the internal intercostals are present (the external intercostals are replaced by membrane in this area).
  4. The internal intercostals are most clinically relevant near the sternum and parasternal area, where they are the only muscular layer.
  • Tissue feel: Indistinguishable from external intercostals on palpation. The combined intercostal tissue feels thin and sheet-like between the ribs.
  • Confirmation test: Ask the client to cough or perform a forced expiration. The internal intercostals contract to depress the ribs. You may feel the intercostal spaces firm up briefly during coughing.
  • Common errors:
  • Attempting to differentiate internal from external intercostals by palpation — this is not clinically feasible and not necessary for treatment.

Trigger Point Referral

  • Common TrP locations: TrPs in the combined intercostal muscle layers are found in the same locations as described for external intercostals — clinically indistinguishable between layers.
  • Referral pattern: Same band-like referral pattern as external intercostals — following the intercostal space around the trunk.
  • Clinical significance: Same as external intercostals — rule out cardiac and visceral causes before treating. Parasternal intercostal TrPs (where only internal intercostals are present) can mimic costochondritis or anterior chest pain syndromes.

Trigger point referral diagram — coming soon

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

Clinical Notes

Common conditions:
  • Cough-related strain — the internal intercostals are maximally activated during forceful coughing. Prolonged coughing episodes (bronchitis, pertussis, COVID-19) can produce intercostal muscle strain and TrPs. These clients present with chest wall pain that worsens with each cough — a self-perpetuating cycle.
  • Parasternal chest wall pain — the parasternal area (adjacent to the sternum) contains only internal intercostal fibers. Tenderness and tightness here can mimic costochondritis (Tietze syndrome) or cardiac pain. Differentiate by location (costochondritis is at the costochondral junctions; intercostal pain is between the ribs) and by cardiac screening.
  • Same thoracic mobility, intercostal neuralgia, and post-surgical conditions as described for anatomy/muscles/external-intercostals.
What you'll typically find:
  • In clients with chronic cough or forced breathing patterns (COPD, asthma), the intercostal muscles are overworked and hypertonic. The intercostal spaces feel tight and restricted, and lateral rib expansion is reduced.
  • Parasternal tenderness is common in clients with anxiety-related breathing disorders — hyperventilation syndrome activates the intercostals excessively, producing bilateral parasternal chest wall pain that the client fears is cardiac.
Treatment effects:
  • Same techniques as external intercostals — gentle sustained pressure and cross-fiber work in the intercostal spaces. The parasternal area responds to gentle contact and sustained compression.
  • In clients with cough-related strain, treatment of the intercostals can break the pain-cough cycle — reducing chest wall pain allows less painful coughing, which reduces further strain.
Cautions:
  • Same cardiac screening requirement as external intercostals — left-sided chest wall pain requires cardiac evaluation before musculoskeletal treatment.
  • The parasternal area is close to the internal thoracic (mammary) artery — this vessel runs vertically approximately 1 cm lateral to the sternum on each side. Avoid sustained deep pressure directly adjacent to the sternal border.
Clinical pearl:
  • In clients who present with bilateral parasternal chest wall pain and a history of anxiety or panic attacks, the intercostal muscles are almost certainly involved. These clients hyperventilate, which overactivates the intercostals (both internal and external), producing chest wall pain that increases their anxiety about having a cardiac event — which triggers more hyperventilation. The treatment is reassurance (after cardiac screening), diaphragmatic breathing retraining, and gentle intercostal release.

Assessment

Manual muscle testing:
  • Not individually strength-tested. Assessment focuses on forced expiratory function and rib cage mechanics.
Stretch test:
  • Same as external intercostals — lateral trunk flexion with arm overhead opens the intercostal spaces.
Related special orthopedic tests:
  • Sternal compression test — anteroposterior compression of the sternum; pain suggests sternal fracture or costochondritis
  • Thoracic expansion measurement

Muscle Groups

Primary respiratory muscles (functional): Intercostal muscles (anatomical):

Related Muscles

Synergist for forced expiration: Antagonist:

Key Takeaways

  • Internal intercostals depress the ribs during forced expiration — they are recruited during coughing, sneezing, and active breathing, not during quiet breathing.
  • Parasternal intercostal TrPs mimic costochondritis and cardiac pain — cardiac screening is mandatory before musculoskeletal treatment of anterior chest wall pain.
  • Cough-related intercostal strain creates a pain-cough cycle — treating the intercostals can break this cycle and reduce overall chest wall pain.

Related

Sources

  • Travell, J. G., & Simons, D. G. (1999). Myofascial pain and dysfunction: The trigger point manual (Vol. 2, 2nd ed.). Williams & Wilkins.
  • Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2023). Clinically oriented anatomy (9th ed.). Wolters Kluwer.
  • Rattray, F., & Ludwig, L. (2000). Clinical massage therapy: Understanding, assessing and treating over 70 conditions. Talus Incorporated.
  • Magee, D. J., & Manske, R. C. (2021). Orthopedic physical assessment (7th ed.). Elsevier.
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