Damage to the bulbospongiosus muscle, a paired skeletal muscle that wraps around the base of the penis in men and the vaginal opening in women, can cause a range of problems from post-void dribbling and weakened ejaculation to sexual dysfunction and perineal pain. The muscle can be injured during childbirth, urethral surgery, pelvic radiation, or through gradual deterioration from diabetes and aging. Because the bulbospongiosus sits deep in the perineum and its symptoms often overlap with other pelvic floor complaints, damage frequently goes unrecognized or gets attributed to something else entirely.
What the Bulbospongiosus Muscle Does
The bulbospongiosus is a paired, striated muscle that originates from the perineal body, the fibrous hub between the genitals and the anus. In men, the muscle fibers wrap around the bulb of the urethra and the corpus spongiosum of the penis. In women, the fibers encircle the vaginal opening and cover the vestibular bulbs. The muscle is controlled by the deep branch of the pudendal nerve, the same nerve bundle that serves several other pelvic floor muscles including the ischiocavernosus and the external urethral sphincter.1PubMed Central. Applied Anatomy of Bulbospongiosus Muscle: a Narrative Review
In practical terms, this muscle has three main jobs. First, it compresses the urethra after urination to expel residual urine, the “milking” action that prevents dribbling. Second, during ejaculation, rhythmic contractions of the bulbospongiosus propel semen through the urethra. Third, the muscle contributes to penile rigidity by compressing the corpus spongiosum, helping maintain erection pressure. In women, it supports vaginal tone and contributes to clitoral engorgement. When the muscle is damaged or denervated, any or all of these functions can be compromised.
Childbirth as a Source of Injury
Vaginal delivery is the single most common cause of bulbospongiosus damage in women. The muscle sits directly in the path of a descending fetal head, and tearing of perineal tissue during delivery almost always involves it. A cohort study that tracked perineal injuries found that every second-degree tear and every episiotomy involved the bulbospongiosus, though not all injuries extended to the nearby superficial transverse perineal muscle.2PubMed. Postpartum perineal pain and dyspareunia related to each superficial perineal muscle injury: a cohort study That distinction matters because the bulbospongiosus and its neighbor serve different functions, and knowing which muscle is torn can help predict which symptoms a woman will experience afterward.
Biomechanical modeling of childbirth has helped explain why the bulbospongiosus is so vulnerable. Researchers have built geometric simulations that include the pelvic floor muscles, the perineal body, and the surrounding structures to map how forces distribute during delivery.3PubMed. A biomechanical perspective on perineal injuries during childbirth Because the bulbospongiosus sits superficially and directly under the vaginal opening, it bears the brunt of the stretching and tearing forces. In many cases, the injury heals adequately with standard perineal repair. But when the muscle heals poorly or the repair does not restore its anatomy, women can experience persistent perineal pain, pain during intercourse, and reduced support of the urethra.
Surgical Damage During Urethral Reconstruction
For men with urethral strictures, surgery to reconstruct the urethra, called urethroplasty, requires the surgeon to work directly through or around the bulbospongiosus. The muscle must be divided or retracted to access the narrowed segment of the urethra underneath. This dissection risks injuring both the muscle fibers and the perineal nerve branches that supply them. In a series of patients who underwent bulbar end-to-end anastomosis, about one in five experienced reduced force of semen emission, and a small number could only ejaculate by manually compressing the perineum. Among patients who had substitution urethroplasty using oral mucosal grafts, roughly 30% reported weaker ejaculation and about half experienced some degree of post-void dribbling.4European Urology. Muscle- and Nerve-sparing Bulbar Urethroplasty: A New Technique
The hypothesis behind these complications is that neural damage to the bulbospongiosus or to the perineal nerves during surgical preparation of the bulbar urethra disrupts the muscle’s ability to contract on command. Without that contraction, the urethral “milking” reflex is lost, and semen emission loses its propulsive force.
Does Muscle-Sparing Surgery Help?
The logical follow-up question is whether deliberately sparing the bulbospongiosus during urethroplasty prevents these problems. Surgeons have developed techniques that split the muscle along its midline rather than transecting it, aiming to preserve more of the nerve supply and muscle bulk. The results, however, have been surprisingly mixed.
An early comparative study found that sparing the bulbospongiosus during urethroplasty did not produce a significant difference in patient-reported ejaculatory function or post-void dribbling compared with the standard non-sparing approach.5PubMed. Functional Effects of Bulbospongiosus Muscle Sparing on Ejaculatory Function and Post-Void Dribbling after Bulbar Urethroplasty A more recent study comparing sparing and non-sparing anastomotic techniques reached the same conclusion: no statistically significant difference in post-void dribbling or ejaculatory outcomes between the two groups.6Scientific Reports. Comparison of postoperative outcomes related to ejaculatory function and post-micturition dribbling between bulbospongiosus muscle sparing and non-sparing anastomotic urethroplasty techniques
The explanation for this counterintuitive finding comes down to anatomy. Most of the bulbospongiosus’s nerve supply and blood vessels enter from the lateral and proximal side of the muscle, not from the midline where the standard technique divides it. So the standard longitudinal split may not actually damage much of the nerve infrastructure. This is reassuring for patients facing urethroplasty, though it also means the muscle-sparing technique’s theoretical advantage has not translated into clear clinical benefit so far.
Diabetes and Gradual Deterioration
Not all bulbospongiosus damage arrives suddenly. Chronic conditions, particularly diabetes, can erode the muscle’s structure over time. An animal study of long-term diabetes found sweeping changes in both the bulbospongiosus and the ischiocavernosus: reduced fiber diameter and volume, lower numerical density of muscle fibers, and significant drops in markers of nerve function. Penile reflexes weakened, and the electrical activity in both muscles declined.7PubMed. Pathobiology of ischiocavernosus and bulbospongiosus muscles in long-term diabetic male rats and its implication on erectile dysfunction The researchers concluded that this combined muscle degeneration and nerve damage plays a major role in erectile dysfunction in diabetes, a finding that makes sense given the muscle’s role in maintaining penile rigidity.
Aging compounds the problem. Research on aging multiparous animals found moderate nerve damage in the bulbospongiosus nerves, including myelin thickening from sheath decompaction and signs of Wallerian degeneration, the process by which a nerve fiber breaks down after losing its connection to the cell body. Younger animals that had given birth showed only mild nerve changes, probably because their nerves could still regenerate effectively. But in older animals, the combination of prior delivery trauma and age-related nerve decline produced measurable damage that the body could not fully repair.8Scientific Reports. Targeted neuromodulation of pelvic floor nerves in aging and multiparous rabbits improves continence
Symptoms That Point to Bulbospongiosus Problems
The most common and recognizable symptom of bulbospongiosus dysfunction in men is post-micturition dribble: the annoying leakage of a few drops of urine after you think you have finished urinating. The dribble happens because urine pools in the bulbar urethra and, without a functioning muscle contraction to squeeze it out, seeps out under gravity once you move. While the full cause of post-micturition dribble is still debated, weakness or failure of the pelvic floor muscles, including the bulbospongiosus, is considered the most important factor.9PubMed Central. A current perspective on post-micturition dribble in males
Weakened ejaculation is the other hallmark symptom. Men with bulbospongiosus damage often notice that semen no longer exits with the same force, or that ejaculation feels incomplete. In severe cases, semen may dribble rather than being expelled. These two symptoms together, post-void dribble and weak ejaculation, are strongly suggestive of impaired bulbospongiosus function, since both depend on the same compressive mechanism.
In women, symptoms of bulbospongiosus injury tend to blend with broader pelvic floor complaints. Persistent perineal pain, especially during intercourse, and a sense of reduced vaginal tone are common after obstetric tears that involve the muscle. Some women also experience mild stress urinary incontinence, since the bulbospongiosus plays a supporting role in urethral closure. MRI-based studies have found that bulbospongiosus thickness is a predictor of pelvic organ support, with thicker muscles showing a strongly protective association against prolapse.10International Urogynecology Journal. 3D MRI Biomarkers for Predicting Pelvic Organ Prolapse Risk and Severity
How Damage Is Assessed
Diagnosing bulbospongiosus damage specifically, as opposed to general pelvic floor dysfunction, usually involves some combination of clinical exam and specialized testing. The bulbocavernosus reflex, triggered by squeezing the glans of the penis or clitoris and watching for an anal sphincter contraction, tests the reflex arc that passes through the bulbospongiosus. An absent or weak reflex suggests damage somewhere along the pudendal nerve pathway or in the muscle itself.11PubMed Central. Applied Anatomy of Bulbospongiosus Muscle: a Narrative Review
Electrophysiologic studies can go further by measuring the electrical activity of the bulbospongiosus directly using needle electrodes, similar to how nerve conduction studies work in the arms and legs. This approach has been used in research on radiation-related erectile dysfunction, where investigators performed electrophysiologic studies of the pudendal nerve and bulbospongiosus muscles before and after pelvic radiation treatment to track nerve damage over time.12PubMed. Pudendal nerve and internal pudendal artery damage may contribute to radiation-induced erectile dysfunction In clinical practice, these studies are less commonly ordered unless the diagnosis is uncertain or the patient is being evaluated before a complex pelvic surgery.
Imaging has also improved. Three-dimensional MRI can now measure bulbospongiosus thickness and identify asymmetry or atrophy, offering objective data about muscle integrity that was previously only available through examination under anesthesia or intraoperative inspection.
Surgical Reconstruction for Congenital Defects
One area where bulbospongiosus repair has shown striking results is in children born with proximal hypospadias, a condition where the urethral opening is located well short of its normal position at the tip of the penis. In these cases, the bulbospongiosus is often malformed or poorly attached, contributing to abnormal penile position and scrotal anatomy.
Surgeons have developed a technique that reconstructs the bulbospongiosus around the bulbar urethra and uses it to anchor the penis to the pubic bones. In a series of 18 patients who had this repair, the base of the penis shifted to a normal anatomical position in every case, and the procedure also corrected penoscrotal transposition, a condition where the scrotum sits in front of the penis. The 15 patients who did not receive the repair during the first stage showed no improvement until the muscle was repaired in a subsequent operation.13PubMed. Repair of the Bulbospongiosus Muscle to Suspend the Penis to the Pubic Bones in Proximal Hypospadias
Long-term follow-up of patients who had this reconstruction and reached puberty has been encouraging. Post-pubertal evaluations found that patients reported a non-dribbling urinary stream, functional erections, and ejectile ejaculations, along with strong satisfaction regarding genital function and appearance.14PubMed. Bulbospongiosus Muscle Reconstruction in Proximal Hypospadias: Post Pubertal Function and Patient Satisfaction These outcomes suggest that when the muscle can be properly positioned and reconstructed early, it can develop normal contractile function over time.
Neuromuscular Stimulation Research
Electrical stimulation of the bulbospongiosus is an active area of research, though most of the evidence so far comes from animal models. Investigators have explored whether stimulating the muscle at different frequencies can alter its contractile behavior. In a rat model, low-frequency neuromuscular electrical stimulation applied to the bulbospongiosus significantly prolonged ejaculation latency compared to both high-frequency stimulation and no stimulation at all. The low-frequency group took roughly twice as long to ejaculate as the control group.15International Journal of Impotence Research. Low frequency neuromuscular electrical stimulation applied to the bulbospongiosus muscle prolongs the ejaculation latency in a rat model
This finding is interesting for two reasons. First, it confirms that the bulbospongiosus can be externally modulated, meaning its contraction patterns are not purely reflexive and can be influenced by targeted stimulation. Second, it raises the possibility that therapeutic stimulation could eventually help men with either premature ejaculation or, at the other end of the spectrum, with weak ejaculation caused by muscle damage. The work on aging animals also supports this idea: targeted neuromodulation of pelvic floor nerves, including those serving the bulbospongiosus, improved continence in older animals with documented nerve damage.16Scientific Reports. Targeted neuromodulation of pelvic floor nerves in aging and multiparous rabbits improves continence Whether these results will translate to humans in a practical clinical device remains to be seen.
Regenerative Therapies on the Horizon
For damage caused by diabetes or other chronic conditions, where the muscle fibers and nerve endings have degenerated over years, the treatment challenge is different from surgical injury. You cannot stitch together what has slowly wasted away. Emerging therapies including low-intensity shockwave treatment, platelet-rich plasma, gene therapy, and stem cell therapy have shown early promise for erectile dysfunction in the context of diabetes, but they all require more robust evidence before they become standard care.17PubMed Central. Erectile Dysfunction in Diabetes Mellitus: A Comprehensive Narrative Review of Pathophysiology, Genetic Association Studies and Therapeutic Approaches The hope is that some of these approaches could restore not just blood flow to the penis, as current treatments like PDE5 inhibitors do, but also the structural integrity of the muscles and nerves that drive erection and ejaculation.
Pelvic floor physical therapy remains the most accessible intervention for mild to moderate bulbospongiosus weakness regardless of cause. Exercises that target the pelvic floor, often called Kegels though the name undersells the specificity involved, aim to strengthen the bulbospongiosus along with its neighboring muscles. The evidence base for pelvic floor training in post-void dribble and mild ejaculatory weakness is modest but consistent enough that most urologists will recommend it as a first step before considering more invasive options.
Pelvic Radiation and Nerve Crossfire
Radiation therapy for prostate and rectal cancers can damage the bulbospongiosus indirectly by injuring the pudendal nerve and internal pudendal artery that supply it. Researchers tracking patients through stereotactic body radiation therapy performed electrophysiologic assessments of the pudendal nerve and bulbospongiosus before and after treatment, alongside ultrasound studies of pelvic blood flow, to identify which structures were being harmed.18PubMed. Pudendal nerve and internal pudendal artery damage may contribute to radiation-induced erectile dysfunction The concern is that radiation-induced erectile dysfunction, long attributed mainly to vascular damage, may also involve denervation of the muscles responsible for maintaining rigidity. If this turns out to be a significant contributor, it could shift how radiation oncologists plan treatment fields, adding the pudendal nerve to the list of structures they try to spare.
This represents a broader shift in how clinicians think about the bulbospongiosus. For decades, it was treated as a minor anatomical detail, something surgeons cut through on the way to more important structures. The growing recognition that its integrity matters for urinary control, sexual function, and ejaculatory mechanics has started changing operative technique, diagnostic workups, and rehabilitation protocols. The muscle’s small size belies its outsized role in functions that patients care deeply about.
Cycling and Perineal Pressure
Cyclists deal with a different mechanism of potential injury. Sitting on a narrow saddle compresses the perineum directly, putting sustained pressure on the bulbospongiosus, the pudendal nerve, and the internal pudendal artery. Over time, this repeated compression can cause numbness, tingling, and in some riders, temporary erectile difficulties. The good news is that the relationship between saddle design and perineal symptoms has been well studied, and practical modifications, specifically wider or cut-out saddles, proper handlebar height, padded cycling shorts, and periodically standing on the pedals, measurably reduce perineal pressure and symptoms.19Quality in Sport. Urogenital Health in Cyclists: Implications for Sports Medicine For most recreational riders, these adjustments are enough to prevent any lasting muscle or nerve damage. Professional cyclists who log extreme hours in the saddle face higher risk, but even in that group, chronic bulbospongiosus injury is uncommon when equipment and position are optimized.