Intercostal muscles are three layers of muscle that fill the spaces between your ribs. You have 11 intercostal spaces on each side of your chest, and each space contains an external, internal, and innermost intercostal muscle working together. Their primary job is breathing, but they also help stabilize your torso and allow your trunk to twist and bend.
Three Layers Between Each Rib
The intercostal muscles are stacked in three distinct layers, each with fibers running in a different direction. This layered design gives the rib cage both flexibility and strength, similar to how plywood gets its durability from alternating grain directions.
The external intercostals are the outermost layer. There are 11 pairs, and their fibers angle downward and forward from the rib above to the rib below. They wrap around the sides and back of the rib cage but don’t extend all the way to the front. Instead, they transition into a thin sheet of connective tissue near the breastbone.
The internal intercostals sit just beneath the externals, with fibers running perpendicular to them. These muscles are concentrated more toward the front of the chest and thin out toward the back, where they become a connective tissue membrane. This opposing fiber direction is key: it lets the two layers pull on the ribs in different ways during breathing.
The innermost intercostals form the deepest layer, lining the inside of the rib cage. They’re thinner and less uniform than the other two layers, sometimes skipping a rib entirely. A thin lining called the endothoracic fascia sits just beneath them, separating the muscles from the membrane that surrounds the lungs.
How They Power Breathing
Every breath you take involves coordinated movement of your ribs, and the intercostal muscles are the main drivers of that motion. When you inhale, your ribs need to swing upward and outward to expand the chest cavity and draw air into the lungs. When you exhale, the ribs move back down and inward.
During quiet, relaxed breathing, you don’t actually use all three layers much. The heavy lifting is done by a specific portion of the internal intercostals called the parasternal intercostals, which sit right next to the breastbone. These muscles contract with every breath to help lift the front of the rib cage and prevent it from being pulled inward by the diaphragm. They work in concert with the scalene muscles in the neck to keep the upper rib cage expanded.
The external intercostals play a smaller role during calm breathing. They function more like a reserve system, activating mainly when you need deeper or faster breaths. During exercise, heavy exertion, or when breathing becomes more difficult, the external intercostals ramp up significantly to pull the ribs higher and expand the chest further. The bulk of the internal intercostals (the portions away from the breastbone) assist with forceful exhalation, compressing the rib cage to push air out more quickly.
Roles Beyond Breathing
The intercostal muscles do more than move air in and out. They contribute to trunk rotation, which matters for everything from throwing a ball to turning in bed. Research published in the Journal of Neurophysiology found that the parasternal intercostals consistently activate during rotation toward the same side, increasing their output to about 152% of their resting activity. When you rotate away from that side, those same muscles quiet down to roughly 83% of baseline. This means the intercostals are actively participating in rotational movements, not just passively going along for the ride.
They also help stabilize the rib cage during lifting, coughing, laughing, and any activity that creates pressure changes inside your chest or abdomen. Without this stabilization, forceful movements would cause the spaces between your ribs to bulge or collapse.
Nerve and Blood Supply
Each intercostal space contains a neurovascular bundle: a nerve, an artery, and a vein running together along the underside of the rib above. The intercostal nerves branch from the spinal cord at levels T1 through T11, providing both motor signals (telling the muscles when to contract) and sensory signals (carrying pain and touch information back to the brain). These nerves also supply sensation to the skin of the chest wall through branches that reach the front and sides of the torso.
Blood reaches the intercostal muscles from two directions. Posterior intercostal arteries supply the back half of each intercostal space, while anterior intercostal arteries (branching from the internal thoracic artery behind the breastbone) feed the front half. These two sets of arteries meet and connect near the middle of each rib, ensuring reliable blood flow even if one route is partially blocked.
Intercostal Muscle Strains
Straining an intercostal muscle is one of the more common causes of chest wall pain. It typically happens from a direct blow to the ribs, a sudden twisting motion, or a rapid increase in physical activity. Overhead sports, heavy lifting, and forceful coughing are frequent culprits.
The hallmark symptom is sharp pain in the rib area that gets noticeably worse with deep breaths, coughing, or sneezing. You may also feel stiffness and muscle tension across the upper back or chest, along with tenderness when pressing on the affected area. Because the pain intensifies with breathing, many people unconsciously shift to shallow, rapid breaths, which can leave you feeling short of breath even though your lungs are fine.
In some cases the pain starts suddenly after an obvious injury, but it can also build gradually over days or weeks from repetitive strain. Swelling and inflammation around the injured muscle are common, and in rare cases a small blood clot (hematoma) can form in the tissue.
Diagnosis is straightforward and based on your history and a physical exam. Imaging like X-rays or MRI isn’t typically needed to confirm a strain, but may be ordered to rule out a rib fracture or injury to internal organs.
Strain vs. Intercostal Neuralgia
Not all pain between the ribs comes from a muscle injury. Intercostal neuralgia is nerve-based pain that can feel similar but behaves differently. Distinguishing between the two matters because the treatments differ.
A muscle strain usually produces localized tenderness that you can pinpoint with your finger, and it worsens with specific movements that stretch or load the injured muscle. Intercostal neuralgia, by contrast, tends to follow a band-like pattern along one or more ribs, often described as burning, stabbing, or tingling. You might notice numbness, extreme sensitivity to light touch, or pain that wraps from the back around to the front of the chest. In some cases, the skin over the affected area changes color or individual muscles twitch involuntarily.
One clinical sign that can help tell them apart is called Schepelmann’s sign. If bending your trunk toward the painful side makes it worse, that points toward compression of intercostal structures like muscles or nerves. If bending away from the painful side is worse, the problem is more likely related to the lining around the lungs (pleurisy) rather than the intercostal muscles themselves.
What Recovery Looks Like
Intercostal strains are frustrating because the injured muscle can’t truly rest. You breathe roughly 20,000 times a day, and each breath engages the intercostals to some degree. That constant low-level use means healing tends to take longer than a comparable strain in your arm or leg.
Mild strains, where the muscle fibers are stretched but not torn, typically improve within a few weeks. Moderate strains involving partial tears can take several weeks to a couple of months. During recovery, the focus is on managing pain well enough to maintain normal breathing depth, since prolonged shallow breathing can lead to reduced oxygen levels and, in some cases, secondary lung complications. Gentle stretching and gradual return to activity help restore normal rib cage mobility as the tissue heals.