How the pelvic floor is built

Understanding the layout makes the rest of this section easier. The pelvic floor is not one muscle but several layers, arranged around three openings, working together with the abdominal wall and the diaphragm.

The frame it sits in

The pelvis is a bony ring. At the front sits the pubic bone, at the back the sacrum and coccyx, and at the sides the two sitting bones. The pelvic floor spans the space between those four points, rather like a hammock fixed at each corner, though it is more accurate to picture a shallow bowl than a flat sheet. Above it sit the bladder at the front, the uterus in the middle and the rectum at the back.

Because the attachments are bony and fixed, the position of the pelvis changes the length of the muscles. Standing with the pelvis tucked under, or gripping the buttocks constantly, holds the floor in a shortened position. Posture is not the whole story, but it is part of it.

The deep layer

The deep layer is usually described as the levator ani group. It has three main parts, named for what they connect: one running from the pubic bone around the rectum, one running from the pubic bone to the coccyx, and a broader fan attached to a thickened band of connective tissue at the side of the pelvis. Together they form the bulk of the pelvic floor and do most of the supporting work.

At rest, these muscles maintain constant low level tone. They are not switched off between contractions, which is why the pelvic floor is described as a postural muscle group. When abdominal pressure rises during a cough, a laugh or a lift, they contract before the pressure arrives, as a reflex. That timing is at least as important as raw strength, and it is one of the first things to be lost.

A little further back sits a small muscle at the side of the pelvis that acts partly as a hip rotator and partly as part of the pelvic wall. It is frequently tender in people with pelvic pain, which is one reason a pelvic pain assessment often includes the hips.

The superficial layer

Closer to the surface, a second set of muscles surrounds the vaginal opening, runs along either side of the vestibule beneath the labia, and forms the ring of muscle around the anus. These muscles are involved in closing the vaginal opening, in engorgement of the clitoral structures during arousal, and in the rhythmic contractions of orgasm.

Between the vaginal opening and the anus lies the perineal body, a dense knot of connective tissue where several muscles converge. It is a small structure that does a great deal of work, and it is the structure most often damaged by tearing or an episiotomy during birth.

The three openings

From front to back: the urethra, roughly four centimetres long in women, which is short enough to explain why urinary infections are more common than in men; the vagina; and the anus. The muscles form functional slings around each. Continence depends on those slings holding closed at rest, and normal function depends on them relaxing fully at the right moment. A muscle that cannot relax produces hesitancy in starting to urinate, incomplete emptying, straining to open the bowels, and pain with penetration.

The nerve supply

The main nerve to the pelvic floor arises from the lower spinal segments and runs a long, winding course through the pelvis, giving branches to the muscles, the anal sphincter, and the skin of the vulva and clitoris. Its route takes it through narrow spaces, which makes it vulnerable to stretch. Prolonged pushing in the second stage of labour, or an instrumental delivery, can stretch it enough to reduce muscle activation for a period afterwards. Recovery is usual, but it takes time, and it is one reason why the pelvic floor immediately after birth feels absent rather than merely weak.

Why it works with breathing

The diaphragm sits at the top of the abdominal cavity and the pelvic floor at the bottom. On inhalation the diaphragm descends and the pelvic floor lengthens slightly; on exhalation both recoil upward. This coupling is why breath holding during exercise raises pressure on the pelvic floor, why breathing work is central to treating an overactive floor, and why exhaling on effort is a useful habit when lifting.

The deep abdominal muscles complete the system. They contract along with the pelvic floor as part of the same anticipatory reflex, which is why an attempt to isolate the pelvic floor perfectly is neither possible nor necessary. What matters is that the contraction is an inward lift rather than a downward push. The exercise page explains how to tell the difference.

What structure predicts

Almost every symptom in this section maps back to the anatomy. Support failure produces prolapse. Sphincter failure produces leaking. Failure to relax produces obstructed voiding, constipation and painful sex. Nerve injury produces temporary or occasionally lasting weakness. Damage to the perineal body produces a scar that can remain tender for months.

Last reviewed: September 2026