What Muscles Cover the Ribs and What Do They Do?

Several layers of muscle wrap around, bridge, and anchor the ribcage, and together they handle everything from breathing to twisting your torso to shielding the organs inside. The most immediate rib-covering muscles are the intercostals, thin sheets sandwiched between each pair of ribs, but much larger muscles like the pectoralis major, latissimus dorsi, serratus anterior, and parts of the abdominal wall also drape over significant portions of the rib cage. Each group has a distinct job, and some of them turn out to work differently from what anatomy textbooks long assumed.

The Intercostal Muscles

The intercostals are the muscles most intimately associated with the ribs because they literally fill the spaces between them. There are three layers in each intercostal space: the external intercostals on the outside, the internal intercostals in the middle, and the innermost intercostals deepest in. You can think of them as a layered mesh, with fibers running at different angles in each layer, much like plywood gains strength from alternating grain directions.

Their primary job is breathing. The external intercostals are traditionally described as inspiratory muscles because their fiber orientation tends to lift and expand the rib cage when they contract. The internal intercostals, especially their bony (interosseous) portions toward the back and sides, are considered expiratory because they pull the ribs downward and inward, helping push air out. But this is a simplification. Research shows that the mechanical advantage of these muscles shifts depending on where in the rib cage you look. The external intercostals in the upper, more dorsal interspaces have a strong inspiratory effect, but that advantage gradually reverses as you move toward the front of the lower ribs. Similarly, the internal intercostals near the sternum, called the parasternal intercostals, actually assist with inspiration rather than expiration.

During quiet, restful breathing, the external intercostals barely fire at all. They ramp up their activity when you breathe harder, whether from exercise, increased carbon dioxide in the blood, or mechanical resistance like breathing through a narrow tube. This has led researchers to describe the external intercostals as something of a reserve system, recruited mainly when the diaphragm needs help expanding the chest more aggressively.

Beyond breathing, the intercostals also stiffen the chest wall. Without them, the spaces between your ribs would simply collapse inward every time the diaphragm contracted and created negative pressure inside the chest. So even when they are not actively driving rib movement, they act as structural bracing that keeps the thorax stable.

The Pectoralis Major and Minor

The pectoralis major is the large, fan-shaped muscle that forms the bulk of the front of your chest. Its lower fibers originate directly from the cartilage of ribs two through six and from the front of the breastbone. Most people think of the pec major as a shoulder and arm muscle, and it is: it powers pushing, hugging, and arm-across-the-body movements. But because it attaches to the ribs, it also plays a role in respiration, particularly during forceful breathing. When you take a deep breath or cough, the pec major helps lift the upper ribs and expand the front of the chest.

Tucked underneath the pec major is the pectoralis minor, a smaller triangular muscle that runs from ribs three through five up to the coracoid process of the shoulder blade. The pec minor stabilizes the scapula by pulling it forward and down, which matters for overhead reaching and throwing. It also helps define the boundaries of the thoracic outlet, the narrow corridor between the chest and armpit through which major blood vessels and nerves pass on their way to the arm.

Tightness in the pectoralis muscles is common, especially in people who spend long hours hunched forward at a desk. When the pec minor shortens chronically, it tips the shoulder blade forward and can compress the structures in the thoracic outlet, contributing to numbness or tingling down the arm. Stretching or manual therapy targeting the pectoralis muscles has been shown to improve chest expansion and, in people with chronic obstructive pulmonary disease, may help reduce respiratory muscle fatigue and improve lung function measures like how much air you can force out in one second.

⁴

Serratus Anterior

Running along the side of the ribcage, from the undersurface of the shoulder blade to the outer surfaces of ribs one through eight or nine, the serratus anterior looks like a series of finger-like strips. It earns the nickname “boxer’s muscle” because it protracts the scapula, pushing it forward and around the rib cage, which is exactly what happens at the end of a punch. It also rotates the shoulder blade upward, which is essential any time you raise your arm overhead.

The serratus anterior is one of the most visible rib-covering muscles in lean, well-developed athletes. When it weakens or its nerve (the long thoracic nerve) is injured, the shoulder blade “wings” out from the back, a condition that looks dramatic and makes it hard to push anything or raise the arm. Because this muscle hugs the lateral rib cage so closely, it also provides a physical cushion over the ribs on the side of the torso, an area otherwise relatively exposed.

The Abdominal Muscles That Reach the Ribs

People tend to think of the abs as belonging to the belly, but the upper fibers of the abdominal wall attach directly to the lower ribs, covering them and anchoring them. The external oblique, the largest and most superficial of the lateral abdominal muscles, originates from the outer surfaces of ribs five through twelve. Its fibers angle downward and toward the midline, interdigitating (interlocking like fingers) with the serratus anterior along the side of the chest.

The external oblique is primarily a trunk rotator and lateral flexor. When the right external oblique contracts, it helps rotate the torso to the left, and vice versa. It also works with the other abdominal muscles to compress the abdominal contents, which assists with forced expiration, coughing, sneezing, and bearing down. Because the external oblique spans such a wide swath of the lower rib cage, it contributes meaningfully to protecting the lower ribs and the organs they shelter, including the lower lobes of the lungs, the spleen on the left, and the liver on the right.

Deeper in, the internal oblique and transversus abdominis also attach to the lower ribs, though they are hidden beneath the external oblique. The transversus abdominis in particular acts like a natural corset, compressing the abdomen from the sides and playing a significant role in forced expiration and core stabilization. The rectus abdominis, the “six-pack” muscle, attaches at its upper end to the cartilage of ribs five through seven and the bottom of the sternum, covering the front of the lower rib cage.

Latissimus Dorsi and the Back Muscles

The latissimus dorsi is one of the widest muscles in the body, and it covers a substantial portion of the back of the rib cage. It originates from the spinous processes of the lower thoracic and all the lumbar vertebrae, the thoracolumbar fascia, the posterior iliac crest, and the lower three or four ribs. From there it sweeps upward and laterally to insert on the upper arm bone.

⁵

The “lats” are best known for pulling the arms downward and backward, the motion you use during a pull-up, a rowing stroke, or reaching into a back pocket. But because the muscle attaches to the lower ribs, it also helps with deep inspiration and forceful respiratory actions like coughing and sneezing, essentially tugging on the lower rib cage to help expand or stabilize it as needed.

⁵

The trapezius and rhomboids, while primarily scapular stabilizers, also lie over the upper portion of the posterior rib cage. They do not attach directly to the ribs in most cases, but they form a muscular blanket over the upper back that indirectly protects the ribs beneath. The erector spinae group, running vertically alongside the spine, covers the posterior ribs from a deeper layer, and its primary role is extending and stabilizing the spine rather than moving the ribs themselves.

The Serratus Posterior Muscles and a Longstanding Myth

Deep to the larger back muscles lie two thin, often overlooked sheets: the serratus posterior superior, which attaches to ribs two through five in the upper back, and the serratus posterior inferior, which attaches to ribs nine through twelve in the lower back. For over a century, anatomy textbooks described the serratus posterior superior as an inspiratory muscle that elevates the upper ribs and the serratus posterior inferior as an expiratory muscle that depresses the lower ribs.

That role has been seriously challenged. Electromyographic studies have failed to show consistent respiratory activity in either muscle. An anatomic investigation comparing these muscles in people with and without chronic obstructive pulmonary disease found no structural differences between the two groups, which you would expect to see if these muscles were genuinely working harder to assist breathing in diseased lungs. The researchers concluded that no respiratory function should be attributed to either the serratus posterior superior or inferior.

⁶

So what do they actually do? The current best guess is that they serve a proprioceptive role, feeding the brain information about rib and trunk position, or they act as tensioning elements that help the deeper respiratory muscles work more efficiently by stabilizing the fascia they attach to. Either way, they are a good reminder that a muscle covering the ribs does not automatically mean a muscle that moves the ribs.

When Rib-Covering Muscles Cause Pain

Because so many overlapping muscle layers cover the ribs, pain in the chest wall can be surprisingly hard to pin down. One well-documented source of rib-area pain involves myofascial trigger points in the intercostal muscles. These are hyperirritable spots within the muscle that, when pressed, produce pain that radiates along the corresponding intercostal space, typically wrapping from back to front. In one clinical investigation, patients who developed these trigger points after a shingles infection of the intercostal nerve experienced pain that followed the rib interspace in the typical distal, anterior direction. Injecting a local anesthetic directly into the trigger point consistently eliminated the pain immediately.

⁷

Trigger points in the intercostals are not limited to post-shingles patients. They can develop from chronic coughing, rib fractures, prolonged poor posture, or repetitive trunk rotation in sports. The pain sometimes mimics cardiac or pulmonary conditions, which is why people with unexplained chest-wall pain sometimes end up in the emergency room before anyone considers a muscular cause. A key distinguishing feature is that myofascial rib pain is reproducible with direct pressure over a specific spot on the chest wall, whereas heart or lung pain typically is not.

Strain of the larger rib-covering muscles is more straightforward but still common. The serratus anterior can be strained by overhead lifting or repetitive reaching. The obliques are vulnerable during explosive rotational movements like swinging a bat or throwing. The intercostals themselves can be strained during violent coughing or sudden twisting, producing sharp pain with every breath that worsens with movement of the torso. In most of these cases, the rib cage is fine; it is the muscle over or between the ribs that is the problem.

Rib-Covering Muscles in Surgery and Reconstruction

The muscles that cover the ribs have a second career in reconstructive surgery. When surgeons need to repair large defects in the chest wall, whether from tumor removal, radiation damage, or trauma, they frequently use the pectoralis major, latissimus dorsi, or rectus abdominis as “workhorse flaps.” These muscles can be rotated or advanced on their blood supply to fill gaps, cover exposed bone or hardware, and restore the structural integrity of the chest.

⁸

The pectoralis major is the go-to flap for defects in the front of the chest and lower neck, largely because of its reliable blood supply and its bulk. The latissimus dorsi, being one of the largest flat muscles in the body, can cover enormous areas and is often the first choice for lateral or posterior chest wall defects. The rectus abdominis can be swung upward on its superior blood supply to reach defects in the lower chest and epigastric region. Surgeons prize these muscles because they can be harvested without catastrophic loss of function; surrounding muscles compensate for the missing one over time, and most patients regain nearly full use of the arm and trunk.

How These Muscles Work Together During Breathing

No single rib-covering muscle handles breathing alone. During a quiet breath in, the diaphragm does most of the heavy lifting by descending and creating negative pressure in the chest. The parasternal intercostals fire at the same time, lifting and stabilizing the upper ribs so they do not get sucked inward. The external intercostals stay mostly quiet unless breathing demand rises.

During a forceful exhale, cough, or sneeze, the picture changes. The internal interosseous intercostals and the triangularis sterni (a thin muscle on the inner surface of the front chest wall) actively pull the ribs down and in. The abdominal muscles contract to push the diaphragm upward from below. And as mentioned earlier, the latissimus dorsi and pectoralis major can pitch in during especially powerful efforts. The coordination across all of these layers is governed by a gradient of neural drive that closely mirrors the mechanical advantages at each rib level, meaning the brain preferentially activates the muscles at the locations where they will do the most good.

This layered, redundant system is why even substantial injury to one muscle group rarely causes total respiratory failure. If the intercostals are damaged on one side, the diaphragm and the abdominal muscles can compensate. If the diaphragm is paralyzed, the intercostals and accessory muscles like the scalenes and sternocleidomastoid can keep air moving, though less efficiently. The ribs are covered not by a single shield but by an interlocking network, and that redundancy is part of the design.

Muscles That Connect to the Ribs Without Really Covering Them

A few muscles commonly confused with rib-covering muscles deserve a brief mention because they attach to the ribs but are not really draped over them in the way the term “cover” implies. The scalene muscles, for instance, run from the cervical spine down to the first and second ribs. They help elevate the upper ribs during breathing, but they sit in the neck rather than on the thorax. The subclavius is a small muscle between the clavicle and the first rib that stabilizes the collarbone during arm movement; it touches a rib but does not cover the rib cage in any meaningful sense.

The diaphragm itself attaches to the inner surfaces of the lower six ribs, and it is technically the most important respiratory muscle of all. But it sits below the rib cage as a dome-shaped partition between the chest and abdomen rather than blanketing the outer surface of the ribs. So while these muscles are functionally linked to the rib cage, they belong to a different anatomical conversation than the layers that wrap around the outside.

1
PubMed. Respiratory action of the intercostal muscles
2
European Respiratory Journal. Respiratory function of the rib cage muscles
3
PubMed Central. Anatomy and Embryology of the Thoracic Outlet
4
International Journal For Multidisciplinary Research. Impact of Neurophysiological Facilitation (Pnf Strech) of Pectoralis Major and Minor Muscle: a Noval Approach to Improve Pulmonary Function in Copd Patient
5
Osmosis. Latissimus Dorsi: What Is It, Location, Function, and More
6
PubMed. An anatomic investigation of the serratus posterior superior and serratus posterior inferior muscles
7
PubMed. Myofascial trigger points in intercostal muscles secondary to herpes zoster infection of the intercostal nerve
8
PubMed Central. Workhorse flaps in chest wall reconstruction: the pectoralis major, latissimus dorsi, and rectus abdominis flaps