A diaphragm is a thin, dome-shaped muscle that separates your chest from your abdomen and powers every breath you take. It’s the primary muscle of respiration, contracting and flattening each time you inhale to pull air into your lungs. The term also refers to a barrier contraceptive device, a flexible cup inserted into the vagina to prevent pregnancy. Both meanings come up frequently, so this article covers each one.
The Diaphragm Muscle: Structure and Location
The diaphragm sits at the base of your rib cage, forming a curved partition between your lungs above and your stomach, liver, and intestines below. It’s remarkably thin, only about 2 to 4 millimeters thick, with a central tendon in the middle and muscle fibers radiating outward from it like the spokes of a wheel.
Those muscle fibers anchor to three areas of your skeleton. The costal portion attaches to the inner surfaces of your lowest six ribs. The lumbar portion connects to your upper lumbar vertebrae (roughly L2 through L4) via thick tendinous bands called crura. And the sternal portion attaches to the bottom of your breastbone. Together, these attachment points create a broad, continuous sheet of muscle that seals the chest cavity from the abdominal cavity, with openings for your esophagus, major blood vessels, and nerves to pass through.
How It Controls Breathing
When you inhale, the diaphragm contracts and pulls downward, flattening from its resting dome shape. This increases the volume inside your chest cavity and creates a pressure drop, essentially a vacuum, that draws air into your lungs. When you exhale, the diaphragm relaxes and springs back up into its dome shape, pushing air out. This cycle happens automatically 12 to 20 times per minute at rest, and much faster during exercise.
The nerve that drives this process is the phrenic nerve, which originates from the third through fifth cervical vertebrae in your neck (C3 through C5). This is why spinal cord injuries at or above C3 can stop a person from breathing independently. The phrenic nerve carries motor signals that trigger contraction, sensory signals that relay information back to the brain, and sympathetic fibers that help regulate the process. Because breathing is controlled by the brainstem, the diaphragm contracts rhythmically without any conscious effort, though you can also override it voluntarily to hold your breath, sing, or blow out candles.
Beyond Breathing: Core Stability and Pressure
The diaphragm does more than move air. It plays a critical role in stabilizing your spine, especially during heavy lifting or sudden exertion. When you brace your core, the diaphragm contracts in coordination with your abdominal muscles and pelvic floor to increase pressure inside your abdomen. This pressurized cylinder of support stiffens your trunk and protects your lower back.
Research on this mechanism found that this cooperative contraction can reduce the load on the upper lumbar spine by about 50% and on the lower lumbar spine by about 30%. It also cuts the strain on your back muscles by more than half. This happens automatically when you lift something heavy, which is one reason physical therapists emphasize diaphragmatic breathing as part of core strengthening programs. The same pressure-building mechanism is what you use during the Valsalva maneuver, bearing down while holding your breath, whether you’re lifting weights, having a bowel movement, or pushing during childbirth.
Diaphragmatic Hernias
A diaphragmatic hernia occurs when abdominal organs push up through a defect or weakness in the diaphragm into the chest cavity. There are two main types.
Congenital diaphragmatic hernias are developmental defects present at birth. The diaphragm doesn’t fully form during fetal development, leaving a gap that allows the stomach, intestines, or liver to migrate into the chest. This can compress the developing lungs and is typically detected on prenatal ultrasound. On the left side, the key finding is that the stomach isn’t visible in the abdomen. On the right side, an abnormal shift of the heart to the left is the most reliable marker.
Acquired diaphragmatic hernias happen later in life, most often after blunt or penetrating trauma such as a car accident or a stab wound. These can also develop after surgery. The most common acquired type in everyday life is a hiatal hernia, where the upper part of the stomach slides up through the opening where the esophagus passes through the diaphragm. Hiatal hernias are extremely common, especially in people over 50, and are a major cause of acid reflux. CT scans are the preferred imaging tool for diagnosing acquired diaphragmatic hernias.
The Contraceptive Diaphragm
A contraceptive diaphragm is a shallow, flexible cup made of silicone or latex that you insert into the vagina before sex. It covers the cervix, creating a physical barrier that blocks sperm from reaching the uterus. It’s used with spermicidal gel, which adds a chemical layer of protection.
Under ideal conditions, with correct placement every time, a diaphragm prevents pregnancy about 94% of the time. With typical use, which accounts for the occasional mistake or inconsistency, effectiveness drops to about 87%. That means roughly 13 out of 100 people using a diaphragm in a typical year will become pregnant.
Fitting, Use, and Care
Diaphragms come in sizes ranging from 60 to 90 millimeters in diameter, and the right size depends on your anatomy. A properly fitted diaphragm sits with its back edge in the deepest part of the vaginal canal behind the cervix and its front edge tucked snugly behind the pubic bone. You should be able to feel the cervix through the dome. A healthcare provider selects the size during a fitting appointment, and you’ll need to be refitted if you gain or lose more than about 15 pounds, after a pregnancy, or after pelvic surgery.
After each use, wash the diaphragm with warm water and mild hand soap, dry it thoroughly, and store it in its case. Avoid talcum powder, baby powder, oil-based lubricants, and silicone-based lubricants, all of which can degrade the material. Leaving a diaphragm in place for extended periods increases the risk of urinary tract infections and has been linked to toxic shock syndrome, a rare but serious bacterial infection.
One limitation worth noting: the spermicide used with diaphragms can irritate the vaginal lining. The CDC notes that this disruption of the tissue may increase the risk of transmitting certain infections, including HIV. A diaphragm does not protect against sexually transmitted infections.