Introduction to the pelvic floor

March 10, 2025
1:20 pm

The pelvic floor is a set of muscles, fasciae and ligaments located in the lower part of the trunk, anchored to the pelvic bones, like a "hammock". Although for a long time it was thought that their only function was to support the pelvic viscera (bladder, uterus and rectum in women; bladder, prostate and rectum in men), it is now known that they perform many other tasks. They are involved in stabilising posture, balance and gait, as well as in breathing, through coordinated action with the abdominal muscles, especially the deep abdominal muscles, and the gluteal muscles. They also collaborate in the physiological functions of the pelvic organs, and in particular in the coordination of urination and defecation. In women, the pelvic floor also plays a very important role during sexual intercourse and childbirth. In men, it plays a role in erection and ejaculation.

The structure and function of the pelvic floor is very complex. Figure 20 Pelvic floor To this day, there is still a great discrepancy between authors, with various nomenclatures and theories regarding micturition and continence mechanisms. For this reason, I will not venture to give more general details on the subject, as it would take several hundred pages to do so. I will focus on its role in micturition, which is, from the point of view of urinary tract infections, what we are concerned with in this book. But before I go into that, I would like to point out the difference between the terms "pelvic floor" and "perineum", because although they are often used interchangeably, they have a different meaning. The perineum is the anatomical region that closes the lower part of the pelvis, while the pelvic floor is a set of muscles, ligaments and fasciae, as I have already mentioned, located in the pelvis (and part of it, in the perineum). It is like imagining that the pelvic floor is the door of the house and the perineum is the façade of that house. The door is integrated into the façade, but the door is not the same as the façade. Therefore, the pelvic floor is not the same as the perineum. However, for practical purposes, these two terms are often used interchangeably, and on this website we will do so.

The role of the pelvic floor in urination

The bladder functions in two phases: voiding and resting. We could also call them the "on" phase (micturition) and the "off" phase (rest). During the off phase, the detrusor muscle of the bladder wall is relaxed, so that the bladder can fill with urine without difficulty. At the same time, the internal sphincter (located in the bladder neck) and the external sphincter (part of the pelvic floor) are contracted. It is important to know that the functioning of the internal sphincter does not depend on our voluntary control, but on the autonomic nervous system, and in particular the sympathetic nervous system (the opposite of the parasympathetic). Thus, we cannot simply ask our internal sphincter to contract more or less. This mechanism will depend on certain reflexes, and will be affected by certain pathologies that affect the autonomic nervous system (central or spinal neurological diseases, stress) or that stimulate the production of more muscle cells at this level, as in the case of prostatic hypertrophy. Men with an enlarged prostate (hypertrophy), a very common pathology from the age of 50-60, often have an internal sphincter that is also hypertrophic. In addition to the difficulty in emptying the bladder due to the obstruction caused by the enlarged prostate at the level of the urethra, there is also hyperactivity of this muscle. This is why the treatment for this problem is often alpha-blocker drugs, which block the alpha-adrenergic receptors of the bladder neck, belonging to the sympathetic nervous system, and relax the muscle.

But back to the pelvic floor, unlike the involuntarily controlled internal sphincter, this set of muscles, and especially the external sphincter of the bladder, can be voluntarily controlled by our brain, via the pudendal nerve. When we feel the urge to urinate and cannot find a toilet, we can voluntarily contract this muscle to prevent urine leakage, even though our bladder is pushing to empty. The same happens if we exert ourselves, cough, laugh, etc.

The external sphincter does not function in an "on" and "off" mode like the bladder, but actually has three positions. Under normal conditions, it is in a state of mild tonic contraction. This allows it to prevent urine leakage when the bladder is filling and the pressure inside the abdomen is not very high. But, if the pressure is increased by any straining, the external sphincter can contract much more to prevent incontinence at that time. On the other hand, when we decide to empty our bladder, the sphincter has to relax completely. It should also be noted that, although it is a voluntarily controlled muscle, its control becomes automatic in childhood. Thus, when we are going to sneeze, we do not have to think "I have to contract my sphincter", but this act is carried out automatically. In the same way, if we want to urinate, our sphincter should be able to relax without us having to actively think about it. (Figure 21). The problem is that many people do not acquire these reflexes correctly, which leads to many urinary problems. This pathology is known as "dysfuctional voiding". It should not be confused with dyssynergia (detrusor-sphincter dyssynergia), which is a pathology of neurological origin, where the external sphincter is constantly contracted, not because of a poorly acquired automatism, but because of an underlying nervous system problem (Parkinson's disease, spinal cord injury, disc herniation, diabetes with peripheral neuropathy, etc.). Although the result is the same, as the bladder has to empty when the "door is closed", the treatment is very different. I am not going to develop the subject of dyssynergia, as these are very complex pathologies that are not the subject of this article. I will focus on explaining voiding dysfunction of non-neurological origin, which is very common and is one of the main causes of urinary tract infections in children and adults. If you want to learn more about it, don't miss the next article.

What is uncoordinated urination?

Uncoordinated micturition is "peeing by squeezing the bum". It has been studied a lot in children, and much less in adults. It is known to be a very common cause of urinary tract infections, daytime incontinence or nocturnal enuresis (bedwetting). It can also cause urethral or pelvic pain in some cases.

It can be diagnosed by various methods. Although the most reliable is the urodynamic study, where bladder and rectal catheters are used to take measurements, as it is an invasive method, it is not usually used as a first diagnostic test. Often, what is done is a flowmetry with perineal EMG. This is a test where the patient is asked to urinate into a device that looks like a toilet while the computer connected to the device forms a graph where it measures the time and force of the urine flow. Figure 22. Previously, before the patient urinates, electrodes are placed on the perineum to measure muscle activity, which will help us to know whether the muscles are relaxed or contracted during urination. It is a simple, non-invasive technique that gives us a lot of information. In fact, I use it every day in my clinical practice. What I usually find, especially in women, where the prostate is not a "confounding factor", are various voiding patterns:

Patients with "normal" micturition where we see a bell-shaped curve and a well relaxed pelvic floor.
Patients with "stacatto" urination, where we see a "sawtooth" curve and a pelvic floor that performs powerful phasic contractions while the patient urinates.
Patients with fluctuating micturition or decreased flow and a pelvic floor with a tonic contraction that does not change before, during, or after micturition. (see figure 23)

The second and third cases are actually different evolutionary moments of the same problem. At the beginning, when uncoordinated urination occurs, we find the second pattern. The bladder has the strength to push hard, even though the pelvic floor makes phasic contractions, and manages to empty completely, often. The third pattern is a more advanced evolutionary stage where, after years of straining to empty, the detrusor muscle of the bladder eventually weakens, as it does in men who have had prostatic hypertrophy for a long time. Eventually, the bladder loses its strength and urination is slow and weak, and often incomplete. Also, the pelvic floor, after years of excessive contraction, loses its powers, especially when it comes to relaxation, and remains in a state of permanent tonic contraction. When we perform voiding re-education to teach patients to relax the pelvic floor, the opposite is usually the case. Those with the third pattern change to the second pattern after a few months, and then from the second to the first. This is because the muscles gradually regain their function.

Why does uncoordinated urination occur?

Let us now discuss the causes of uncoordinated urination of "non-neurological" origin. This problem is multifactorial. It may simply be due to a poorly acquired reflex at the time of nappy removal, where the child does not automate the voluntary relaxation of the external sphincter while urinating, and tends to do the opposite, contracting the pelvic floor during urination. Often, these are children who have been quite precocious in the removal of nappies (around the age of two or earlier) and who are used to squeezing their tummy to urinate. They are usually withholding children, who have to be insisted on a lot to go to the toilet, and are often associated with constipation, due to the same mechanism (they do not know how to relax the anal sphincter properly during defecation). They may have good daytime and night-time continence, or they may have good daytime continence but wet the bed. Sometimes they also have symptoms of overactive bladder (small urine leaks during the day, children often cross their legs to avoid wetting themselves, or episodes of "jiggle incontinence" or giggle incontinence). In these children there is usually no organic cause, and it is known that the most effective treatment is voiding re-education by a physiotherapist or nurse expert, with a programme called "biofeedback", which will be discussed in the second part of the book. With this programme, it is possible to modify the automatism and make the patient relax the sphincter correctly during urination. It is important to treat children with this problem, as it is known that, if they have not received treatment, the risk of having voiding problems in adulthood is very high. In fact, I always ask patients who consult for UTIs if they have had voiding problems in childhood or adolescence, and they often tell me that they have had infections or bedwetting, but that it was never treated. Many also refer to chronic "lifelong" constipation.

Another cause of uncoordinated urination is urinary retention, whether it is voluntary (people who report going to the toilet because they are busy or because they dislike using public toilets, for example) or work-related, as certain jobs do not allow us the freedom to go to the toilet when we need to. These people usually have an enormous bladder capacity, they can store more than half a litre of urine without hardly having the urge to urinate. They tend to voluntarily contract the sphincter to "hold back the urge", and this ends up becoming a reflex. Then, when they have to relax it to urinate, they do not succeed, and often voluntarily or involuntarily squeeze their belly to urinate, which in turn causes further contraction of the sphincter. Sometimes they complain of small "paradoxical" urine leaks. This is because, being constantly contracted, the sphincter loses the ability to perform a maximum contraction when abdominal pressure increases (the three sphincter positions, remember?). So when they strain, cough or laugh, they leak a little urine even though they have a very strong sphincter. This is a problem because many women with uncoordinated urination that is not accompanied by infections but by urinary leakage consult a gynaecologist or urologist because of this problem. If uncoordinated urination is not suspected and an EMG flowmetry or urodynamic study is not performed, they are likely to end up having surgery (suburethral sling) unnecessarily, when the problem is not a deficit of pelvic floor muscle tone, but rather the opposite. Typically, these patients do not improve after surgery, or they improve, but later the incontinence recurs and is accompanied by other problems such as infections, pain or urinary retention.

A loss of pelvic statics can also lead to dysfunctional urination. It is important to know that pelvic statics depends on the condition of the pelvic muscles, but also of the abdominal, lumbar and diaphragm muscles, as well as on the balance of the bony part, especially the pelvis and hips. Any problem that throws this out of balance can lead to pelvic floor muscle dysfunction. Examples would be childbirth or pelvic or abdominal surgery (vaginal, perineal or abdominal approach), abdominal hyperpressure caused by chronic coughing or very intense physical exercise, or skeletal or motor alterations of the lower limbs. When a person has osteoarticular pain in the hip, knee, foot, etc., he or she often adopts what we call an "antalgic posture" to avoid pain when supporting that limb. The same happens if one of the two lower limbs is shorter than the other, either naturally or after trauma or surgery. In all these cases, the pelvis will no longer be horizontal and will tilt to one of the two sides, breaking the balance and pelvic statics (this is called hip dysmetry). I have had many patients who have started to suffer from urinary tract infections, incontinence, urinary or faecal retention immediately after having such a problem, and they have been greatly improved by physiotherapy for their pain or by using an orthopaedic insole to rebalance the hip.

I would like to mention other causes of uncoordinated urination such as pain or psychological problems. These are patients who have suffered a local problem (severe infection, painful surgery, trauma, sexual assault or other) and who, due to persistent pain or as a defence mechanism, have developed hypertonia of the pelvic floor muscles. It is a complicated situation, because here, in addition to the muscular and coordination problem, psychological factors are involved, which overload patients a lot and which must be treated at the same time, otherwise there will be no improvement. I would like to clarify that emotional stress can be an important cause of uncoordinated urination, which acts at the level of both sphincters. The internal sphincter is controlled by "alpha adrenergic" receptors in the bladder neck. These nerve receptors respond to commands from the sympathetic system via the neurotransmitter noradrenaline (a cousin of adrenaline). The sympathetic system is the part of the autonomic nervous system that is activated in situations of stress and alertness. Thus, in a situation of chronic stress our sympathetic system will be constantly over-activated and will send a lot of noradrenaline to our internal sphincter, preventing it from relaxing. This is logical if we think about what the sympathetic response is for in an evolutionary way, because when we were prehistoric hominids, this response was activated when we felt threatened by a danger such as a wild animal attack, for example. At that point, there was no place to urinate, of course. So our sympathetic system would make us hold our urine (and faeces too, for that matter) so that we would then be running away or fighting and not relieving ourselves. The problem is that today's chronic stress overactivates our sympathetic system and causes a certain chronic hypertonicity of the internal bladder sphincter. The external sphincter is also affected by this response because, although it is controlled by the pudendal nerve rather than the sympathetic system, it is known that some of the muscle fibres of both sphincters are intermingled and often act together.

Why can uncoordinated urination lead to urine infections?

By what mechanism does uncoordinated urination cause urine infections? You may ask. It is obvious that if a person does not manage to empty their bladder correctly due to this voiding dysfunction, and there is always urine trapped inside, they will be more at risk of suffering from infections, as the urine will be full of bacteria that are not eliminated with each urination. But what about all those people who have uncoordinated micturition but do manage to empty their bladder completely? What about those who have uncoordinated urination but do not have infections?

The mechanism is easy to understand. When urine passes through the urethra during urination, if there is a simultaneous contraction of the sphincter, the urethra will be "strangled" and the urine, especially the last drops, will make "up and down" movements as it passes through the urethra, a bit like a dropper. It will then reach the vagina, where it will be contaminated with local micro-organisms, and then be absorbed into the bladder, taking these germs with it. If the vaginal microbiota is composed of protective lactobacilli, urine infection will not occur even if there is uncoordinated urination. But if the vagina contains uropathogenic bacteria, they will pass into the bladder by this "dropper" phenomenon and probably cause an infection. Therefore, for a UTI to occur in these cases, two circumstances must be present at the same time: uncoordinated micturition and vaginal dysbiosis.

In conclusion, uncoordinated micturition of non-neurological origin is an extremely common pathology. It often starts in childhood or adolescence but, if not symptomatic, goes completely unnoticed until adulthood or old age when it starts to cause problems. In my clinical practice I routinely perform EMG flowmetry on people consulting for UTIs, and about nine out of ten have uncoordinated micturition. In other articles I will discuss some treatment strategies for this common problem.

I don't like my toilet...

I have to tell you about the toilet bowl. Yes yes, the wc, the toilet. It turns out that, from my point of view, a very important cause of urinary tract infections is the use of sitting toilets (i.e. "normal" toilets). This is again related to pelvic floor statics, muscle relaxation and urethral alignment. It is important to know that our natural way of urinating, at least in the case of women, is squatting. This position favours relaxation of the pelvic floor and alignment of the bladder neck with the urethra. However, if we sit at 90° and, above all, if our knees are below our hips (which is the most common position when we sit on the toilet), this relaxation and alignment will not occur, and urination is likely to be dysfunctional. This is why Turkish toilets (those that are nothing more than a kind of hole in the floor), although they look disgusting, allow for a much more physiological way of urinating. (figure 24). As I know that most people don't have this type of toilet at home or at work, and don't want to call the plumber to install it, in future articles I will give you a few useful tips on how to adopt the correct position.

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