The intercostal muscles are three layers of muscle that sit between your ribs, forming much of the chest wall. You have 11 pairs on each side of your ribcage, and their primary job is driving the mechanical act of breathing by expanding and compressing your rib cage. They also help stabilize your torso during twisting and bending movements.
Three Layers, Three Different Roles
The intercostal muscles are stacked in three distinct layers between each pair of ribs, running from superficial (closest to the skin) to deep (closest to the lungs).
The external intercostals are the outermost layer. Their fibers angle downward and toward the front of your body. When they contract, they lift the ribs outward and upward, expanding the width of your chest in what’s sometimes called a “bucket handle” motion. This is the muscle layer most responsible for pulling air into your lungs during normal breathing. The external intercostals run from the back of the ribcage to the point where the bony ribs meet cartilage near the breastbone, where they transition into a thin sheet of connective tissue.
The internal intercostals form the middle layer. Their fibers run perpendicular to the external layer, angling downward and toward the back. When these muscles contract, they pull the ribs downward and inward, compressing the chest cavity and pushing air out. They’re most active during forceful exhalation, like blowing out candles, coughing, or exercise. The internal intercostals span from the breastbone in front to the back of the ribcage, essentially covering the opposite territory from the external layer.
The innermost intercostals are the deepest layer, separated from the internal intercostals by a thin space containing the intercostal nerves and blood vessels. Their inner surface sits just outside the membrane lining your lungs. These muscles work alongside the internal intercostals during forced exhalation, though they’re thinner and less powerful.
How They Power Breathing
The classic textbook explanation is straightforward: external intercostals breathe in, internal intercostals breathe out. The reality is more nuanced. Research published in The Journal of Physiology found that the external intercostals have their strongest inspiratory effect in the upper ribcage, particularly toward the back. But this effect diminishes as you move lower and toward the front of the chest. In the lower interspaces (around the sixth to eighth rib gaps), the external intercostals actually produce a small expiratory effect instead.
Similarly, the internal intercostals are strongest as expiratory muscles in the lower front portion of the ribcage. Their expiratory power decreases as you move upward and toward the back. If all segments contracted at full force, the internal intercostals would still produce a net expiratory effect across the entire ribcage, but the contribution varies significantly by location.
During quiet breathing at rest, the external intercostals do most of the active work alongside the diaphragm. Exhalation at rest is largely passive, driven by the natural elastic recoil of the lungs and chest wall. The internal and innermost intercostals kick in primarily during forceful breathing, such as during exercise, singing, or coughing.
Trunk Stability and Rotation
Beyond breathing, the intercostal muscles contribute to stabilizing and rotating the trunk. The parasternal intercostals, a portion of the internal intercostals near the breastbone, are consistently active when you rotate your torso toward the same side. They fall silent during rotation to the opposite side. This means your intercostal muscles are working during activities like throwing, swinging a bat, or twisting to reach something behind you. They help hold the ribcage rigid so that force generated by your core and limbs transfers efficiently rather than being lost to a floppy torso.
Nerve and Blood Supply
Each intercostal space has its own nerve, artery, and vein running in a bundle along the underside of the rib above. The intercostal nerves branch from the spinal cord at levels T1 through T11, one for each space. These nerves supply the intercostal muscles themselves and also carry sensation from the overlying skin, which is why a problem in one intercostal nerve can cause pain that wraps around the chest wall in a band-like pattern.
Blood reaches the intercostal muscles from two directions. The front of each space is fed by branches of arteries running behind the breastbone, while the back of each space receives blood from branches of the aorta. These two supplies connect in the middle, ensuring a reliable blood flow even if one side is compromised.
Intercostal Muscle Strain
Strains of the intercostal muscles are common and often result from sudden twisting, reaching overhead, or heavy lifting. Forceful coughing or sneezing can also do it. The hallmark symptom is chest pain that gets worse with movement, deep breathing, or coughing. You may also notice tenderness when pressing on the affected area, pain when moving your arm on that side, and occasionally bruising, swelling, or visible muscle spasms.
Recovery time depends on severity. A mild strain, where fibers are stretched but not torn, typically heals within a few days. A moderate strain involving partial tearing of muscle fibers generally takes 3 to 7 weeks. A severe strain with complete tearing of the muscle can take longer, though most rib-area muscle injuries resolve within about 6 weeks. Rest, ice, and over-the-counter pain relievers are the standard early approach, followed by gradual return to activity as pain allows.
One of the more frustrating aspects of intercostal strains is that you can’t fully rest the injured muscle because you need to breathe. Shallow breathing feels easier in the short term but can lead to complications if it goes on too long. Gentle, controlled deep breaths, even though they hurt, help maintain lung function during recovery.
Intercostal Neuralgia
Intercostal neuralgia is nerve pain that follows the path of one or more intercostal nerves, producing a sharp or burning sensation that radiates along the rib. The most common cause is shingles, a reactivation of the chickenpox virus. The nerve pain that lingers after a shingles outbreak, called post-herpetic neuralgia, affects an estimated 3.2 people per 1,000 each year. Other causes include rib fractures and surgical procedures that involve opening the chest.
Treatment typically starts with anti-inflammatory medications and physical therapy. If those aren’t enough, medications that calm nerve signaling, such as certain antidepressants or anti-seizure drugs, are commonly used. More resistant cases may involve nerve blocks, radiofrequency treatments to disrupt pain signals, or electrical nerve stimulation.
Chest Wall Pain vs. Pleurisy
Because the intercostal muscles sit right over the lungs, muscle pain in this area can feel alarmingly similar to lung problems. Pleurisy, an inflammation of the membrane surrounding the lungs, also causes sharp chest pain that worsens with breathing. The key difference: pleuritic pain typically lessens or stops entirely when you hold your breath, because the inflamed membranes stop sliding against each other. Intercostal muscle pain, by contrast, is usually reproducible by pressing on the sore spot or by specific movements of the arm or trunk. Pleuritic pain may also spread to the shoulders or back and is often accompanied by fever or a cough, pointing to an underlying infection or inflammatory condition rather than a muscle problem.