The Anatomy of the External Intercostals

Muscles Which Assist With Breathing

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The external intercostals are small muscles located in between each rib, starting at the first rib and extending down to the 11th rib. The motions of these muscles assist the lungs by raising the ribs and expanding the chest cavity. This added room in the chest cavity allows for the lungs to fill with air each time a person takes a breath in. The suffix ‘-costal’ indicates the muscles are involved with motion of the ribs, where ‘inter-’ states the location of the muscles is between each rib.


There are two sets of intercostal muscles within the rib cage. External intercostals can be found on the surface, just below the skin, and provide muscle contractions which assist with inhalation. Internal intercostals can be found in the layer of muscles directly below the external intercostals. Internal intercostals assist with exhalation and moving the ribs and chest cavity back to their original position. These muscles combine to fill in the space between each rib and provide support for the respiratory system.

Since external intercostal muscles are small but relatively powerful muscles, each extends from the bottom to the top of each rib. This location allows the external intercostals to lift the ribs upward and spread them apart. These motions make space for the lungs to expand with the air the intercostals helped bring to the body.

The health and functioning of the spine is also dependent on appropriate contraction of the intercostal muscles. This interaction is largely due to how each rib wraps around the body and ends near the spine.

External intercostals receive nerve signals from the intercostal nerves, which stem from the spinal cord. Each external intercostal muscle is supplied with blood from three major arteries.

Anatomical variations of the external intercostal muscles are most often related to differences in the sizes of the ribs, sternum, and other bony structures in the chest cavity. Variable sizes and shapes of these bones may cause the external intercostals to be too large or too small to accommodate the respiratory needs of the individual.


The external intercostals are the more surface-level muscles in between the ribs which serve to elevate the rib cage and assist the lungs in expanding to take in air. Due to the role intercostal muscles play in elevating the ribs and expanding the chest cavity, their contraction must be triggered in order to allow for timely access to the lungs.

The external intercostals play a large role in the respiratory system. However, due to the small size of the external intercostal muscles, there are several other muscles in the upper body which assist with movements related to rib cage adjustments. Serratus posterior and pectoralis minor muscles assist with raising the upper ribs. The sternocleidomastoid muscle, which comes from the jaw and crosses over the neck, moves the breastbone upward. Scalene and latissimus dorsi muscles in the upper back also assist with raising the shoulder blade to add extra space in the rib cage.

Intercostal spaces between the ribs are often punctured during a thoracostomy, which is a procedure used to remove fluid from the lungs.

Associated Conditions

As with any muscle, the external intercostals can be strained as a result of too much stress or pressure. It is easy to mistake a strained external intercostal for a back or neck injury, as this is where most of the symptoms will appear. Someone with strained external intercostals will experience sharp pain to the upper back and ribs. This pain will worsen with coughing, sneezing, and breathing deeply. This will cause a person’s ribs to be tender with the possibility of spasming external intercostals. The presence of pain over specific ribs will help eliminate the confusion between a strained upper back and strained external intercostals.

The cause of strained external intercostals is typically too much exertion or direct injury to the muscles via assault or respiratory conditions. Repetitive activities such as twisting in yoga, golf, tennis, and weight-lifting can also cause strain to the external intercostals. Similarly, jobs which require repetitive motions, such as overhead lifting and carrying heavy objects can also cause this injury. While participation in these activities does place someone at risk for straining such muscles, this injury often occurs in individuals who are overall weakened due to lack of exercise or a prolonged illness.

Doctors can diagnose strained intercostal muscles through a physical exam. Since sharp pain may be the cause of a fractured rib, a doctor may perform an X-ray to make a definite diagnosis. Medical treatment of strained intercostal muscles includes the use of heat and ice to reduce swelling, rest and activity limitations, along with pain medications. Doctors may recommend muscle relaxers for individuals who are experiencing spasms of the intercostal muscles. If swelling and pain persists after five to seven weeks, doctors may use anti-inflammatory injections as second-line treatments.


Physical therapy and occupational therapy are often recommended to rehabilitate intercostal muscles which may have been strained due to lack of activity or poor posture. Therapy for this type of injury often focuses on pain management with the integration of strengthening programs. These strengthening programs will improve posture, build endurance levels, and improve a person’s breathing patterns.

Maintaining healthy patterns such as these will cause an individual to heal more quickly from a strain of this type. This rehabilitation will also serve to prevent future injuries to the external intercostal muscles.

4 Sources
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  2. Donley ER, Loyd JW. Anatomy, thorax, wall movements. StatPearls Publishing.

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  4. Yoo WG. Effect of a combined thoracic and backward lifting exercise on the thoracic kyphosis angle and intercostal muscle pain. J Phys Ther Sci. 2017;29(8):1481–1482. doi:10.1589/jpts.29.1481

By Brittany Ferri
Brittany Ferri, MS, OTR-L, CCTP, is an occupational therapist, consultant, and author specializing in psychosocial rehab.