Incomplete bowel emptying usually stems from a coordination problem between the muscles of the pelvic floor and the rectum, though structural changes, sluggish colonic movement, nerve damage, medications, and even toilet posture can all play a role. The medical term for the sensation is “incomplete evacuation,” and it is one of the most common complaints gastroenterologists hear. What makes it frustrating is that several distinct mechanisms can produce the same feeling, and more than one can be operating at the same time.
Pelvic Floor Muscles That Work Against You
The single most studied cause of incomplete evacuation is a condition called dyssynergic defecation. Normally, when you bear down on the toilet, the muscles of your pelvic floor relax while your abdominal muscles push. In dyssynergic defecation, the pelvic floor muscles contract at exactly the wrong moment, or fail to relax enough, creating a kind of muscular tug-of-war. Research shows that most people with this condition demonstrate an inability to coordinate the abdominal, rectoanal, and pelvic floor muscles during defecation, with the failure taking the form of inadequate pushing force, paradoxical contraction of the anal sphincter, or insufficient sphincter relaxation.1Journal of Neurogastroenterology and Motility. Diagnosis and Treatment of Dyssynergic Defecation Clinically, this has been defined as inappropriate pelvic floor contraction or less than 20% relaxation of the resting sphincter pressure during a pushing attempt.2PubMed. Obstructed defecation syndrome associated with paradoxical puborectalis contraction: osteopathic treatment versus anal biofeedback
What makes dyssynergic defecation tricky is that many people develop it without any obvious injury or illness. Some researchers believe it is a learned behavior pattern, possibly stemming from years of straining, ignoring the urge to go, or chronic holding. Others point to the fact that psychological stress can exacerbate or even trigger pelvic floor dysfunction, which then alters bowel habits and feeds a cycle of anxiety around toileting.3PubMed Central. Biofeedback Treatment Can Improve Clinical Condition and Quality of Life in Patients with Pelvic Floor Dyssynergy with Irritable Bowel Syndrome: A Prospective Cohort Study The reassuring news is that it is one of the most treatable causes, a point covered later in the article.
Structural Changes in the Rectum
Even when the muscles coordinate properly, the anatomy of the rectum itself can prevent full emptying. Two structural conditions stand out: rectocele and rectal intussusception.
A rectocele is a bulging of the front wall of the rectum, usually into the back wall of the vagina in women. During a bowel movement, stool can push into this pocket rather than traveling downward, leaving the sensation that something is still there. Rectoceles are extremely common findings on imaging, and symptoms most often include pelvic pressure and difficulty passing stool.4PubMed Central. Functional Disorders: Rectocele In a study of 52 women with evacuation difficulty, those with a rectocele had significantly more incomplete rectal emptying and slower rectal evacuation times than those without one, and the deeper the rectocele, the longer the emptying took.5PubMed. Dyschezia and rectocele–a marriage of convenience?
An interesting nuance: not all rectocele symptoms are actually caused by the rectocele. One study found that vaginal digitation, the need to press against the vaginal wall to help evacuate stool, was the only symptom specifically linked to a true rectocele. Other obstructed-defecation symptoms were more closely associated with stool consistency than with the rectocele itself.6PubMed. Rectocele or stool quality: what matters more for symptoms of obstructed defecation? In practical terms, this means that if your main complaint is incomplete emptying but you don’t need to manually assist stool out, your rectocele may be an incidental finding rather than the root cause.
Rectal intussusception is a different problem: part of the rectal wall folds inward on itself during straining, creating a partial blockage. People with this condition often present with constipation and incomplete evacuation, though some have no symptoms at all.7PubMed Central. Functional Disorders: Rectoanal Intussusception The invaginated tissue essentially acts as a plug, and the rectum cannot push past it efficiently.
When the Colon Itself Moves Too Slowly
Before stool even reaches the rectum, it has to travel through the colon. In slow transit constipation, the colon’s propulsive contractions are reduced, which means stool sits in the colon for far longer than it should. This leads to harder, drier stool that is more difficult to evacuate and can leave behind a persistent sense of fullness. Slow transit constipation is estimated to account for roughly 15 to 30% of cases among people who are chronically constipated.8PubMed Central. Slow transit constipation: a review of a colonic functional disorder The proposed causes involve problems with the autonomic and enteric nervous systems or a dysfunctional neuroendocrine system in the gut wall itself.
This is a condition defined by markedly delayed transit through the colon, leading to fewer bowel movements, abdominal discomfort, and a significant hit to quality of life.9PubMed Central. Slow Transit Constipation: Pathophysiological Perspectives and Management Updates People with slow transit constipation often describe a general feeling that their bowels never fully clear, which makes sense physiologically: if the colon is not contracting with enough force or frequency, residual stool accumulates. Slow transit and pelvic floor dysfunction can coexist, and when they do, treating only one of them often leaves the person still symptomatic.
Reduced Rectal Sensation
Your rectum relies on nerve signals to tell your brain when it is full and when it has finished emptying. When those signals are blunted, a condition called rectal hyposensitivity, you may not sense a full rectum until it is overly distended, and you may stop pushing before the rectum is truly empty. Rectal hyposensitivity is defined clinically by elevated sensory thresholds to rectal distension and is linked to both constipation and fecal incontinence.10PubMed Central. Rectal hyposensitivity The cause can be a primary disruption of nerve pathways, secondary to changes in rectal wall mechanics (a stretched-out rectum after years of constipation becomes less sensitive), or a combination of both.
What this looks like in daily life is someone who goes to the bathroom, passes some stool, never quite feels “done,” and sometimes does not feel the urge at all until the rectum is uncomfortably full. It is one of the more underrecognized causes of incomplete evacuation because it is invisible on standard imaging and requires specialized testing to identify.
Neurological Conditions
The bowel is heavily wired into the nervous system, so neurological diseases frequently affect evacuation. People with spinal cord injury, multiple sclerosis, and Parkinson’s disease present with serious bowel dysfunction characterized by constipation, incontinence, impaired motility, and altered visceral sensitivity.11PubMed Central. Neurogenic bowel dysfunction in patients with spinal cord injury, myelomeningocele, multiple sclerosis and Parkinson’s disease In these cases, incomplete evacuation is part of a broader pattern called neurogenic bowel, where both the sensory signals and the motor commands to the colon and rectum are disrupted.
Even milder nerve involvement can contribute. Diabetes that has caused peripheral neuropathy, for instance, can slow colonic transit and dull rectal sensation. If incomplete evacuation develops alongside a diagnosed neurological condition, the bowel dysfunction is rarely coincidental.
Medications and Metabolic Conditions
Several categories of medication slow the gut enough to cause incomplete emptying. Opioid painkillers are the most notorious, but antipsychotics, certain antidepressants, iron supplements, calcium channel blockers, and antacids containing aluminum all slow intestinal motility. Drug-induced gastrointestinal disorders can mimic conditions like irritable bowel syndrome, and recognizing the medication as the culprit can prevent unnecessary testing and treatment.12PubMed Central. Drug-induced gastrointestinal disorders
On the metabolic side, hypothyroidism is a classic offender. An underactive thyroid slows gastrointestinal movement through neuromuscular dysfunction, hormonal changes, and structural modifications to the intestinal wall, including thickening of the muscular layer and shortening of intestinal villi.13PubMed Central. Integrated Management of Constipation in Hypothyroidism: Evaluating Pharmacological and Non-Pharmacological Interventions If constipation and incomplete evacuation appeared around the same time as fatigue, weight gain, or cold intolerance, thyroid function is worth checking.
Descending Perineum Syndrome
Years of chronic straining can weaken the connective tissue that supports the pelvic floor, causing the perineum to descend excessively during pushing. This descent changes the angle between the rectum and the anal canal, making effective evacuation harder and encouraging even more straining, which worsens the descent further. In a study of 39 patients with this condition, almost all reported constipation, incomplete rectal evacuation, and excessive straining, and about a third needed to use their fingers to assist evacuation.14PubMed. Descending perineum syndrome: audit of clinical and laboratory features and outcome of pelvic floor retraining Testing in that group showed abnormal perineal descent in 78% and abnormal changes in the rectoanal angle during defecation in 57%.
The increased pressure that comes from straining at an abnormal angle essentially works against productive evacuation.15PubMed Central. Clinical Features and Associations of Descending Perineum Syndrome in 300 Adults With Constipation in Gastroenterology Referral Practice It is a self-reinforcing problem: incomplete evacuation causes straining, straining causes descent, descent causes worse evacuation.
Pregnancy, Childbirth, and Pelvic Trauma
Pregnancy itself places significant mechanical and hormonal stress on the pelvic floor, and delivery can compound the damage. In a study of 30 women treated surgically for obstructed defecation syndrome, about two-thirds had delivered vaginally and the remainder had cesarean sections. The women who had cesarean sections actually had higher obstruction scores before surgery, suggesting that pregnancy and delivery trauma alone, independent of vaginal delivery, can contribute to pelvic floor dysfunction.16PubMed Central. Obstructed Defecation Syndrome After Delivery Trauma This is a finding that surprises many women who assumed a cesarean would protect them from pelvic floor problems. The weight and hormonal changes of pregnancy appear to be enough on their own to alter pelvic anatomy.
Toilet Posture Matters More Than You’d Think
The modern sitting toilet places your body in a position that works against easy evacuation. When you sit upright at roughly 90 degrees, the puborectalis muscle only partially relaxes, keeping a kink in the path between the rectum and the anal canal. A scoping review of research on toilet postures found that squatting results in a straighter rectoanal canal and requires less straining than standard sitting.17PubMed Central. Sitting vs. squatting: a scoping review of toilet postures and associated health outcomes You don’t need to install a squat toilet to benefit from this. Leaning forward and placing your feet on a low stool to bring your knees above hip level mimics much of the angle advantage of squatting.
For someone whose incomplete evacuation is primarily postural, this is a remarkably simple fix. For someone with dyssynergia or a rectocele, it may help but won’t solve the problem on its own. Still, posture is the lowest-cost, lowest-risk adjustment available, and it’s worth trying before pursuing anything more involved.
The Role of Psychological Stress
The gut-brain axis runs in both directions. Chronic constipation and pelvic floor dysfunction can contribute to anxiety and depression, and psychological stress can in turn exacerbate or even trigger pelvic floor problems.3PubMed Central. Biofeedback Treatment Can Improve Clinical Condition and Quality of Life in Patients with Pelvic Floor Dyssynergy with Irritable Bowel Syndrome: A Prospective Cohort Study This bidirectional relationship helps explain why some people find their evacuation difficulties worsen dramatically during stressful periods. It also explains why purely mechanical treatments sometimes fail: if the nervous system is perpetuating a pattern of pelvic floor tension, addressing only the muscles without addressing the stress can leave the cycle intact.
How Doctors Figure Out the Cause
Because so many different problems produce the same symptom, diagnosing the underlying cause requires specialized testing. The two most common tools are anorectal manometry, which measures pressures and coordination patterns in the rectum and anal canal, and the balloon expulsion test, which assesses whether you can push a small inflated balloon out of the rectum within a set time. Diagnosing dyssynergic defecation requires a dyssynergic pattern on manometry along with at least one other abnormal test, such as the balloon expulsion test or defecography, which is an imaging study that shows the rectum in motion during a simulated bowel movement.18PubMed. Defecation Symptoms in Relation to Stool Consistency Significantly Reflect the Dyssynergic Pattern in High-resolution Anorectal Manometry in Constipated Patients
Each test has strengths and weaknesses. The balloon expulsion test had a specificity of about 82% for diagnosing dyssynergic defecation in one comparative study, while high-resolution manometry had a specificity of roughly 53%.19PubMed Central. High-Resolution Anorectal Manometry and Balloon Expulsion Test Outcomes in Functional Constipation: A Comparative Study That’s why guidelines call for more than one abnormal test before assigning the diagnosis. Defecography is particularly useful for identifying structural causes like rectoceles and intussusception, which manometry cannot detect.
For slow transit constipation, a different approach is needed. Transit studies, where you swallow markers that are tracked on X-rays over several days, can show whether the colon is moving contents at a normal speed. Blood work for thyroid function, calcium levels, and other metabolic causes is a routine part of the workup as well.
Treatment That Targets the Mechanism
The right treatment depends entirely on which mechanism is causing the problem, which is why accurate diagnosis matters so much.
For dyssynergic defecation, biofeedback therapy is the frontline treatment. Biofeedback uses sensors to give you real-time visual or auditory feedback on your pelvic floor muscle activity, essentially teaching you to relax the right muscles at the right time. Studies show that biofeedback improves both the percentage of anal sphincter relaxation and clinical symptoms like constipation and quality of life in patients with pelvic floor dyssynergia, regardless of whether they also have irritable bowel syndrome.3PubMed Central. Biofeedback Treatment Can Improve Clinical Condition and Quality of Life in Patients with Pelvic Floor Dyssynergy with Irritable Bowel Syndrome: A Prospective Cohort Study The improvements are not just in lab measurements; constipation scores and lifestyle scores dropped significantly in treated patients.
For structural causes like rectocele and intussusception that have not responded to conservative management, surgery becomes an option. A technique called stapled transanal rectal resection (STARR) has shown good results for obstructed defecation caused by these anatomical problems. In one study, constipation symptoms improved in 90% of patients at one year after the procedure, with most rating their outcome as good or excellent.20PubMed Central. Stapled transanal rectal resection for obstructed defecation syndrome associated with rectocele and rectal intussusception Surgery is generally reserved for cases where biofeedback, dietary changes, and other conservative approaches have not worked.
Sacral neuromodulation, a technique that uses a small implanted device to deliver mild electrical pulses to the nerves controlling the bowel, is an emerging option for more refractory cases. It has shown significant improvements in bowel function scores and quality of life in patients with dysfunction following rectal surgery.21PubMed Central. Sacral neuromodulation improves bowel function in patients with low anterior resection syndrome The technique has also been studied in irritable bowel syndrome, where it significantly reduced symptoms and improved quality of life in carefully selected patients.22PubMed. A randomized, controlled, crossover study of sacral nerve stimulation for irritable bowel syndrome
When Stool Consistency Is the Real Culprit
Before pursuing extensive testing, it is worth considering the simplest explanation: stool that is too hard or too loose can create a false sensation of incomplete emptying even when the pelvic floor and rectum are working normally. Hard stool fragments and breaks apart during passage, leaving pieces behind. Very loose stool can coat the rectal walls without fully evacuating, producing a persistent sense of urgency. The finding that many obstructed-defecation symptoms track more closely with stool consistency than with structural abnormalities is a useful reminder that fiber intake, hydration, and diet deserve attention first.6PubMed. Rectocele or stool quality: what matters more for symptoms of obstructed defecation?
A trial of increasing soluble fiber (psyllium husk is the best studied), adequate water intake, and regular physical activity resolves symptoms for a substantial number of people and costs nothing. If those measures do not help within a few weeks, that’s when specialized evaluation becomes worthwhile.