The pelvic floor consists of a layer of muscle and fibrous tissue which extends across the lower part of the bony pelvis from the lower edge of the symphysis pubis to the tip of the sacrum. It is a complicated and important structure permitting the passage of urine and faeces and is perforated in front by the urethra leading down from the bladder, and behind by the rectum and anal canal. The vagina perforates the pelvic floor at approximately its mid-point. It would be difficult to design a man-made structure to be perforated by the urethra, vagina and rectum and yet to be strong enough to prevent all the abdominal organs from falling out of the bottom of the pelvis. It must also be remembered that the pressure within the abdomen, and therefore on the pelvic floor, increases to quite an extraordinary degree during coughing or sneezing, as well as during exercise and especially when straining to open the bowels.
The main structure of the pelvic floor is a pair of muscles called the levator ani. These stretch from each side wall of the pelvis, joining together in mid-line to form a type of hammock or sling across the pelvic outlet, and are supported by layers of fibrous tissue both above and below. During the actions of coughing and sneezing the levator ani muscles actually contract and thus give a special support to the pelvic outlet. The fact that these muscles can relax in order to allow the baby to pass through the pelvis is truly remarkable. As the baby’s head passes through the pelvic floor the levator ani muscles and their associated fascia are folded sideways against the walls of the pelvis and, providing they are not badly damaged, they will rapidly return to their normal and natural state after delivery.
Postnatal exercises are, however, most important in restoring the tone and strength of the muscles.