This post was written by H&W instructor Allison Ariail PT, DPT, CLT-LANA, BCB-PMD. Allison will be instructing the Pelvic Floor Level 1 course Boston this October.
Several weeks ago some of my fellow faculty members and I were discussing the resting tone of the pelvic floor. These days we take it for granted that we know there is constant low-level activity in the pelvic floor and anal sphincter in order to provide continence. However, how did this information come about? I took it upon myself to do some research to find out the beginnings of this knowledge. What I found was interesting and thought I would share.
In the late 1940’s and early 1950’s the belief was held that the pelvic floor and external anal sphincters were inactive at rest, like other striated muscle throughout the body. Activity was believed to be initiated by afferent impulses from the rectal ampulla and anal canal. In 1953 Floyd and Walls found activity in the external anal sphincters at rest, even during sleep. In 1962 Parks, Porter, and Melzak published a study examining the pelvic floor muscles and the external anal sphincters using electromyography recordings. They also found activity in these muscles at rest. They hypothesized the activity was maintained by spinal reflex. These researchers looked at the activity in a healthy population, a paraplegic population, and a population that had undergone a rectal excision. When examining the paraplegic population (all subjects had complete SCI injuries above L3), they did identify activity of the pelvic floor at rest.
With respects to the rectal excision population, they examined patients whose rectums were removed, but the somatic muscles, external sphincters, and the levator ani remained with innervation intact and the muscles were sutured to provide a muscular pelvic floor. These patients also exhibited activity in the pelvic floor and anal sphincter at rest. These patients were important to the study in order to rule out that the reflex was not coming from somewhere in the rectal wall. Additionally, these researchers discovered this resting activity that was present the anal sphincter was inhibited during defecation in response to a certain degree of rectal distension.
So what did all of this new information mean to these researchers? It meant that the pelvic floor and external anal sphincter were unique due to the fact they were activated at rest, and without this activation continence would not be maintained. They determined the activation to be reflex and termed it “postural reflex of the pelvic floor.” Additionally, they termed the inhibition due to rectal distension “the rectal inhibitory reflex,” which also was due to a reflex arc. This new information was groundbreaking for the time and lead to other research that provided us with the knowledge that we have today! Thank goodness for these researchers as well as the many others who have furthered the advancement of knowledge about the pelvic floor!
Learn more about Allison and the Pelvic Floor Series by visiting our website!
1. Floyd, Walls. Electromyography of sphincter ani externus in man. J. Physiol. 122: 599, 1953.
2.Parks, Porter, Melzak. Experimental study of the reflex mechanism controlling the muscles of the pelvic floor. Dis. Colon Rectum. 5 (6): 407. 1962.