The muscles between and around your ribs are called the intercostal muscles. There are 11 pairs of them, one set in each space between adjacent ribs, and they’re the primary muscles responsible for expanding and contracting your rib cage as you breathe. A few other muscles also attach directly to the ribs, including the serratus anterior, which you can see and feel along the side of your torso.
The Three Layers of Intercostal Muscles
The intercostal muscles aren’t a single sheet. They’re arranged in three distinct layers stacked on top of each other, each running in a slightly different direction. Think of them like plywood, where alternating grain directions create strength.
The external intercostals are the outermost layer, sitting just beneath the skin and surface tissue. Their fibers angle downward and toward the center of your chest. These are the muscles that do the heavy lifting when you breathe in. They pull your ribs upward and outward, expanding your rib cage. That expansion increases the volume inside your lungs and creates suction that draws air in.
The internal intercostals form the middle layer. Their fibers run perpendicular to the external layer, angling in the opposite direction. These muscles are most active when you breathe out forcefully. When they contract, they pull the ribs closer together, shrinking the rib cage and pushing air out of your lungs. They’re especially engaged when you cough, sneeze, or sigh.
The innermost intercostals are the deepest layer, lining the inside of the rib cage closest to your lungs. They’re thinner and less well-defined than the outer two layers, and they assist the internal intercostals during exhalation. The intercostal nerves and blood vessels run in the small gap between the internal and innermost layers.
How Breathing Actually Works
During quiet, relaxed breathing, your diaphragm (the dome-shaped muscle below your lungs) does most of the work. The external intercostals assist by lifting the ribs slightly with each inhale. Normal exhaling is largely passive: your rib cage and lungs simply recoil back to their resting position.
Forced breathing is where the intercostals really kick in. During exercise, when you’re breathing hard, the external intercostals contract more aggressively to pull the ribs wider. On the exhale, the internal intercostals actively squeeze the rib cage down to push air out faster. This is also what happens when you blow out candles, play a wind instrument, or cough hard enough to clear your airways.
Other Muscles Attached to Your Ribs
The intercostals aren’t the only muscles on the rib cage. Several larger muscles originate or insert on the ribs and serve different purposes.
The serratus anterior is the most visible one. It’s a fan-shaped muscle that originates on the outer surfaces of ribs one through eight (or nine) and wraps around the side of your torso to attach to your shoulder blade. You can feel it by placing your hand just below your armpit. On lean or muscular people, it appears as a series of finger-like segments along the side of the rib cage, sometimes called “digitations” because they look like spread fingers gripping the ribs. Its main job is pulling the shoulder blade forward and rotating it to let you raise your arm overhead. When your shoulder is braced, it can also help lift the ribs during heavy breathing.
The pectoralis minor is a smaller chest muscle that attaches to ribs three through five and connects up to the shoulder blade. It pulls the shoulder blade forward and downward, and can assist with breathing when your shoulder is stabilized. The subcostalis muscles are small, variable muscles on the inner surface of the lower ribs that help depress the ribs during exhalation. They’re not present in everyone and are too deep to feel from the outside.
What Controls These Muscles
The intercostal nerves, which branch off the spinal cord from the upper and mid-back (thoracic vertebrae T1 through T11), run through each intercostal space and control the rib muscles. Each nerve supplies the muscles, skin, and lining tissue in its corresponding rib space. The lower intercostal nerves (from the seventh through eleventh ribs) continue beyond the rib cage into the abdominal wall, which is why a rib injury can sometimes produce pain that seems to wrap around into your belly.
Intercostal Muscle Strains
If you’ve ever felt a sharp pain between your ribs after twisting, coughing hard, or overexerting during exercise, you may have strained an intercostal muscle. These strains are one of the most common causes of rib-area pain, and they can feel alarming because the pain worsens every time you breathe.
Typical symptoms include sharp pain in the upper back or rib area, tenderness when pressing between the ribs, stiffness when twisting or bending your torso, and pain that gets worse with deep breaths, coughing, or sneezing. Muscle spasms between the ribs are also common. The pain can come on suddenly from a direct blow or develop gradually from repetitive movements like rowing or swimming.
Recovery time depends on severity. A mild strain often heals within a few days. Moderate strains, where more muscle fibers are torn, typically take three to seven weeks. A severe strain involving a complete muscle tear takes longer. Most rib muscle injuries resolve within about six weeks. Rest, ice, and gentle stretching as pain allows are the standard approach. The tricky part is that you can’t fully rest these muscles since you need them to breathe, which is why rib strains tend to feel persistent and annoying even when they’re healing normally.
How to Feel Your Rib Muscles
You can locate your intercostal muscles by pressing your fingertips into the spaces between any two ribs on the side of your chest. The tissue filling those gaps is the intercostal muscle. It’s thin, so you’re mostly feeling the outermost (external) layer. If you press while taking a deep breath, you may feel the muscles tighten slightly as they work.
The serratus anterior is easier to identify visually. Place your hand on your side, just below your armpit and in front of your latissimus dorsi (the large back muscle). If you push your arm forward against a wall, you’ll feel the serratus engage and firm up along the side of your rib cage. The distinct finger-like segments that give this muscle its serrated appearance are separated by bands of connective tissue, and they become more visible as body fat decreases.