Pelvic floor dysfunction (PFD)is a common postpartum condition with substantial impact on women’s quality of life, physical function, and psychosocial well-being. Epidemiological evidence shows that PFD symptoms are highly prevalent. A study in southern China reported that the overall prevalence of uterine/organ prolapse among postpartum women at 6 weeks was 72.83%(1). A meta-analysis based on 32 studies involving a total of 28303 women estimated the incidence of postpartum urinary incontinence to be 26%(2). More research indicates that within 10 years after giving birth, approximately 50% of women experience PFD(3). These findings demonstrate that PFD is not a transient postpartum issue but an enduring health burden that requires effective and individualized rehabilitation strategies.

Many obstetric and maternal factors, such as vaginal delivery, multiparity, increased infant birth weight, and higher maternal body mass index are closely related to postpartum pelvic floor dysfunction(4, 5). These risk factors underscore the importance of timely assessment and targeted rehabilitation after childbirth. Given the high burden and multifactorial nature of PFD, effective postpartum rehabilitation is critical. Biofeedback electrical stimulation(BES), often combined with pelvic floor muscle training༈PFMT༉, has gained widespread use as a conservative intervention. Electrical stimulation can cause passive contractions of the pelvic floor muscles, activate the neuromuscular pathway and enhance muscle excitability. A randomized controlled study demonstrated that after multiple treatments with transvaginal electrical stimulation, patients showed significant improvement in EMG indicators such as contraction amplitude and endurance stage(6). Biofeedback provides visual or auditory cues to help patients learn how to actively recruit pelvic floor muscles, improve contraction patterns, and enhance motor control and endurance. Studies of BFES combined with pelvic floor function exercise revealed that compared with the simple exercise group, the combined group had more significant improvements in electromyographic activity, stress urinary incontinence and pelvic organ prolapse(7, 8). However, despite its overall effectiveness, clinical outcomes following BFES are not uniform across all patients. Several studies have reported limited or inconsistent treatment effects, particularly among women with more severe pelvic floor impairment at baseline. For example, a randomized controlled trial found that pressure-mediated biofeedback combined with PFMT improved objective cure rates but did not significantly improve pelvic floor muscle strength or quality of life, suggesting a limited response in some subgroups(9). Similarly, for pelvic organ prolapse, evidence suggests that although BFES may improve functional outcomes, anatomical improvements assessed by pelvic organ prolapse quantification༈POP-Q༉are often minimal(10). This indicates that BFES may not adequately reverse structural pelvic floor damage, especially in women with more advanced prolapse or fascial defects. A 2024 meta-analysis on BFES for postpartum stress urinary incontinence further highlighted high heterogeneity and publication bias, emphasizing that not all patients benefit equally from BFES(11). These findings align with clinical observations that pelvic floor muscle recovery is highly dependent on baseline strength, neuromuscular integrity, and severity of dysfunction.

Taken together, these findings highlight the necessity of precise stratification and personalized rehabilitation strategies in the management of postpartum pelvic floor dysfunction. The modified oxford scale(MOS)provides a clinically meaningful classification of pelvic floor muscle strength and can be used to identify patients with low functional reserve who may respond differently to BFES(12). Therefore, the present study aims to evaluate the differential efficacy of a standardized 15-session BFES intervention between postpartum women with low and moderate baseline pelvic floor strength. By comparing changes in MOS scores, surface electromyography parameters, and POP-Q measurements between strength-stratified groups, this study seeks to provide evidence for precision-based postpartum pelvic floor rehabilitation. Identifying which subgroups benefit most or least from BFES will contribute to the development of more individualized, efficient, and clinically meaningful postpartum care pathways.

Baseline demographic and obstetric characteristics including maternal age at delivery(95%CI: -2.61-0.22, Cohen’s d = 0.37, postpartum body mass index༈BMI)༈95%CI : -1.30-0.21, Cohen’s d = 0.22༉, mode of delivery༈Cramér’s V = 0.07༉, parity ༈Cramér’s V = 0.23༉, and infant birth weight༈Cohen’s d = 0.17༉ did not differ significantly between low-grade group and moderate-grade group (p > 0.05) ༈Table 1༉.

After 15 sessions of biofeedback-assisted electrical stimulation, both groups demonstrated significant improvements across primary and secondary outcomes. MOS scores increased significantly from baseline in both the low-grade group (pre: 0.89 ± 0.57 vs. post: 2.60 ± 0.94, Cohen’s d = 0.86) and the moderate-grade group (pre: 2.39 ± 0.46 vs. post: 3.90 ± 0.61, Cohen’s d = 0.87). Significant improvements were noted in POP-Q points Aa and Ba in the low-grade group (pre: -1.24 ± 0.82 vs. post: -2.01 ± 0.79, Cohen’s d = 0.79)and in the moderate-grade group ༈pre: -0.93 ± 0.79 vs. post: -1.56 ± 0.79, Cohen’s d = 0.72༉. POP-Q points C in the low-grade group ༈pre: -5.45 ± 0.91 vs. post: -5.94 ± 0.33, Cohen’s d = 0.53༉and in the moderate-grade group ༈pre: -5.1 ± 1.07 vs. post: -5.78 ± 0.62, Cohen’s d = 0.59༉were also significantly different. Other POP-Q points remained stable without significant deterioration༈Table 2༉. Both groups exhibited significant differences between pre-treatment and post-treatment in sEMG parameters during the pre-baseline༈the low-grade group: Cohen’s d = 0.27, the moderate-grade group: Cohen’s d = 0.45༉, flick contraction ༈the low-grade group: Cohen’s d = 0.72, the moderate-grade group: Cohen’s d = 0.59༉, tonic contraction ༈the low-grade group: Cohen’s d = 0.79, the moderate-grade group: Cohen’s d = 0.77༉, endurance contraction ༈the low-grade group: Cohen’s d = 0.75, the moderate-grade group: Cohen’s d = 0.65༉, and post-baseline ༈the low-grade group: Cohen’s d = 0.28, the moderate-grade group: Cohen’s d = 0.14༉༈Table 3༉.

Despite significant within-group improvements, no statistically significant differences were observed between the low-grade and moderate-grade groups in the magnitude of change for any primary or secondary outcome. Specifically, the mean change in MOS scores did not differ between the two groups (ΔMOS: low-grade 1.72 ± 0.78 vs. moderate-grade 1.51 ± 0.62, r_rb = 0.16). Similarly, changes in POP-Q points Aa, Ba, and C༈Table 2༉, as well as improvements across all Glazer EMG phases including pre-baseline༈Cohen’s d = 0.26༉, flick contraction༈r_rb = 0.07༉, tonic contraction༈r_rb = 0.14༉, endurance contraction༈r_rb = 0.04༉ and post-baseline༈r_rb = 0.11༉were comparable between the two groups ༈all p > 0.05༉༈Table 3༉.

In this study, both the low‑grade and moderate‑grade pelvic floor dysfunction groups demonstrated significant within-group improvements in pelvic floor muscle strength, anatomical support (POP‑Q points), and surface electromyography parameters after 15 sessions of biofeedback‑assisted electrical stimulation. These findings suggest that BFES is effective across different baseline levels of pelvic floor impairment. Studies have shown that biofeedback electrical stimulation can effectively awaken nerve cells that have lost their conduction function, accelerate the conduction speed of pelvic floor nerves, increase the strength of pelvic floor muscles, help restore and maintain the stability of urethra and bladder functions, and has a specific effect on improving vaginal laxity and urinary incontinence in patients(14). During the treatment process, patients experience muscle contractions, and the series of electromyographic activities formed thereby can be further transformed into visually distinctive images. Doctors guiding pelvic floor muscle function training based on feedback information is conducive to enhancing the purposefulness and pertinence of practical training, enabling patients to independently grasp the contraction situation and improve their subjective initiative(15). Clinical trials and meta-analyses provide human evidence that is consistent with these mechanisms. A meta-analysis included 1,362 people with postpartum stress urinary incontinence and found that biofeedback electrical stimulation could effectively improve the quality of life of patients with PSUI by significantly enhancing the contraction and relaxation abilities of pelvic floor muscles(16). A randomized trial show that intravaginal electrical stimulation added to bladder training or pelvic floor muscle training improves clinical symptoms, pad-test and quality-of-life measures in women with urinary symptoms(17). Another randomized trial found that bladder training plus intravaginal electrical stimulation༈VES༉produced greater symptom and quality of life improvements than bladder training alone in women with idiopathic overactive bladder(18). Likewise, a recent randomized trial in post-reconstructive pelvic surgery patients showed that postoperative ES combined with EMG biofeedback improved objective pelvic floor muscle EMG parameters, digital palpation scores and patient-reported distress scores compared with usual care(19).

Both study groups showed within-group improvements after a standardized 15-session biofeedback electrical stimulation program. This pattern is biologically plausible because the vaginal nerve and the external urethral sphincter are simultaneously injured during vaginal delivery, which is a unique complex neuromuscular injury(19). Electrical stimulation(ES)produces activity-dependent trophic and regenerative responses in injured peripheral nerves and their target muscles, accelerating axonal outgrowth and neuromuscular reinnervation in animal models of childbirth-related injury; for example, pudendal nerve stimulation increases expression of brain-derived neurotrophic factor in pudendal motor neurons and improves external urethral sphincter activity and leak-point pressure in a rat model of stress urinary incontinence(20). Moreover, increasing the frequency of ES further accelerates functional recovery in the same preclinical paradigm, suggesting a dose-dependent regenerative effect that plausibly translates into measurable clinical gains over a short treatment course(21). At the cellular level, brief periods of electrical stimulation have been repeatedly shown to trigger gene programs that speed axonal regeneration and improve the accuracy of motor reinnervation—mechanisms that can restore neuromuscular continence mechanisms after birth injury and therefore produce measurable improvements in pelvic floor function(22). Biofeedback contributes complementary mechanisms that help explain within-group gains. By providing real-time information about pelvic floor muscle contractions, biofeedback facilitates correct voluntary recruitment and repetitive practice. Extensive animal and translational work show that repetitive, task-specific motor training induces cortical and spinal plasticity that consolidates improved motor control. Studies of motor skill training in rodents and reviews of motor-learning-related plasticity indicate that practice drives structural and functional reorganization in motor cortex and spinal circuits—mechanisms that plausibly underlie improved voluntary pelvic floor control following biofeedback-guided training(23).

Stratifying participants by baseline pelvic floor muscle strength using the MOS provides a physiologically and clinically relevant framework for evaluating the efficacy of BFES. Evidence indicates that baseline muscle strength is a key determinant of postpartum pelvic floor recovery. Several clinical studies suggest that lower pelvic floor muscle strength, as assessed by MOS or pressure measures, is associated with obstetric history and body composition. Longitudinal data have shown that parity and higher BMI are linked to decreased pelvic floor muscle strength over time, indicating that maternal history and weight status influence muscle capacity postpartum(24). Additionally, cohort studies have found that increased infant birthweight predicts reduced pelvic floor pressure after delivery, further highlighting obstetric and body-related factors as determinants of initial muscle capacity in postpartum rehabilitation research(25, 26). Similarly, a systematic review highlighted that variations in baseline PFM strength contributed to heterogeneity in clinical outcomes across PFMT and BFES studies, supporting stratification to better detect differential responses(27).

In the present study, both low- and moderate-strength groups demonstrated significant within-group improvements after 15 BFES sessions. This may be explained by the capacity of electrical stimulation to recruit motor units even in muscles with limited voluntary contraction. A cohort study comparing pelvic floor exercise with or without electrical stimulation reported greater improvements in perineometer-measured contraction pressure and duration in the ES group, suggesting that ES can enhance muscle activation irrespective of initial strength(28). Thus, participants with low MOS grades may achieve functional gains comparable to those with moderate grades, reducing detectable differences between groups.

Several additional factors may explain the lack of significant between-group differences. First, the short-term intervention may be insufficient to produce structural changes or long-term functional divergence. Prior studies have shown that while ES and PFMT improve muscle strength and symptom scores over weeks, anatomical outcomes such as prolapse stage often remain unchanged in short follow-ups(29). Previous clinical trials and systematic reviews suggest that conservative therapies such as PFMT with or without ES predominantly improve neuromuscular activation and functional outcomes such as muscle strength, endurance, EMG parameters, whereas changes in structural endpoints, such as pelvic organ prolapse stage, are less likely to be detected in short-term protocols, so between-group differences in structural endpoints may be absent even when functional gains occur(30, 31). Secondly, outcome measurement sensitivity may limit detection of subtle differences; tools such as MOS may not capture small but clinically relevant changes, particularly over brief interventions(32). Thirdly, the complexity of pelvic floor dysfunction—including connective tissue damage, fascial disruption, and potential nerve injury—means that BFES predominantly targeting muscle activation may not fully address underlying structural or neurogenic deficits, which could attenuate between-group differences(33).

From a clinical perspective, these findings suggest that BFES is effective across a range of baseline PFM strengths, supporting its broad applicability in postpartum rehabilitation. Stratification by MOS remains important for understanding patient-specific responses and for tailoring intensity or adjunctive interventions. However, for long-term structural recovery or prevention of recurrence, extended or multimodal rehabilitation programs may be necessary, particularly in women with more severe anatomical or neuromuscular compromise. Limitations of this study include the relatively short follow-up, potential insensitivity of functional measurements to subtle changes, and lack of imaging-based assessment of structural damage. Future studies should incorporate longer follow-up periods, standardized and sensitive outcome measures, and consider additional stratification by obstetric history, levator ani integrity, and connective tissue status to more accurately predict response to BFES.

This study demonstrates that a standardized 15-session biofeedback electrical stimulation intervention significantly improves pelvic floor muscle function in postpartum women, regardless of baseline muscle strength as assessed by the modified oxford scale. Both low-strength and moderate-strength groups showed meaningful improvements in pelvic floor muscle strength, surface electromyography parameters, and select POP-Q measures. However, no significant differences were observed between groups, suggesting that BFES can effectively enhance neuromuscular activation across a spectrum of initial pelvic floor function. The findings support the clinical utility of BFES as a broadly applicable postpartum rehabilitation strategy, while emphasizing the importance of individualized assessment and ongoing monitoring. Future studies with longer follow-up, multimodal interventions, and more sensitive structural and functional assessments are warranted to optimize treatment efficacy and durability, particularly in women with more severe pelvic floor compromise.