Urinary incontinence has a global prevalence of 8.7% worldwide [1]. It is more common in women, experienced by 10% - 20% of all women and 77% of older women inhabiting nursing homes [2-7]. Despite the high prevalence, only about a quarter of women with urinary incontinence seek medical care, with only half of them eventually receiving treatment [8].

Stress urinary incontinence (SUI) is the most common etiology of urinary incontinence, defined as the involuntary loss of urine during physical activity that increases abdominal pressure. Stress urinary incontinence occurs when there is a failure of the urinary sphincter to withstand the pressure inside the bladder or failure of support of the lower urinary tract (bladder neck and urethra), resulting in urethral hypermobility. Both could happen concurrently, usually resulting from neurological disease, trauma, previous surgery, or in ageing women [9]. Physicians are required to explore risk factors including age, obstetric history, gynecological status, previous illnesses, daily activities, and pharmacological status in patients with urinary incontinence.

The treatment of SUI may include both non-surgical and surgical methods. Surgical therapy is typically utilized in patients who have failed non-surgical treatment, have moderate or severe SUI, poor quality of life, or have pelvic organ prolapse [10]. Traditional open surgery or minimally invasive surgery (laparoscopic) approach of Burch colposuspension, mid-urethral synthetic slings such as tension-free vaginal tape (TVT), trans obturator tape (TOT), and urethral bulking agents are among the procedures available [10-12]. Sling surgery is considered to be the current gold standard for treating SUI [10]. Lately, SUI treatment using stem cell therapy has a promising potential to improve the mechanism of urethral sphincter insufficiency, but further studies are needed in order to clarify the role of cell-based therapies for the treatment of SUI patients [13, 14]. The type of intervention should be tailored to the patient's symptoms, level of discomfort, goals and expectations, as well as the risks and benefits [12].

Patients more often choose conservative treatments rather than more invasive ones [15]. Pelvic floor muscle training (PFMT) is indicated for women with stress urinary incontinence, with less efficacy for urgency incontinence [16]. Aiming to improve pelvic floor muscle function, PFMT includes various exercises directed toward maximizing functional capabilities, including Kegels. Arnold Kegel first utilized Kegels to enhance the strength of floor muscles in 1940, and it is still widely used [17, 18]. Exercise may be done supervised or at home, with the latter currently emerging as it is more cost-effective [19]. Physicians use several ways to assist patients while exercising with electrostimulation, biofeedback (BF), and vaginal cones. Biofeedback is the most commonly used monitoring method for PFMT, with some studies showing no benefit from using BF augments [19-23]. Thus, the effectiveness of these adjunctive modalities remains unclear.

This study aims to systematically review and quantitatively analyze selected randomized controlled trials that evaluate PFMT and biofeedback-assisted pelvic floor muscle training (BPFMT) for patients with stress urinary incontinence.

Summarization of the article selection process (Fig. 1) was conducted based on PRISMA guidelines. Initial database searching resulted in 1361 studies, and all were assessed using the EndNote application for study duplication. According to our inclusion criteria, the remaining 571 studies were then assessed manually by all authors. As many as thirteen articles were further analyzed for eligibility, resulting in five articles finally being analyzed qualitatively and quantitatively [24-28]. The outcomes analyzed in this study were: change of pelvic muscle floor (PFM) strength, incontinence episode, daytime micturition, and nighttime micturition. All data were pooled as mean difference (MD) since all of them were continuous data.

3.1. Study Characteristics

The analyzed studies were conducted in 4 different countries, two from Brazil, and the remaining three were from Germany, Japan, and Turkey (Table 1). A total of 96 patients received biofeedback as an adjuvant to PFMT, and 111 patients received PFMT alone. The duration of the intervention varied from 4 weeks to 12 weeks. When reported, the studies used different biofeedback methods and instruments.

Fig. (1). PRISMA flow chart.

Table 1. Study characteristics and outcome.

Study Authors	Year	Country	Design	Sample Size		Age	BMI (kg/m2)	Training Period	Outcome	BF Method
				BPFMT	PFMT Only
Pages, et al.	2001	Germany	RCT	13	27	51.1	N/A	4 weeks	Perineometry, daytime micturition, nighttime micturition, incontinence episode	Supine, intravaginal + sensor using Gemini 2000TM apparatus. Five times per week for 4 weeks, each for 15 minutes.
Aksac, et al.	2003	Japan	RCT	20	20	52.5	N/A	8 weeks	Perineometry, incontinence episode, 1 hour pad test, VAS, PFM strength from digital palpation	Lithotomy, intravaginal + sensor using Myomed-932. Three times per week for 8 weeks, each for 20 minutes.
Schmidt, et al.	2009	Brazil	RCT	10	11	53.3	30.3	12 weeks	Perineometry, daytime micturition, nighttime micturition, KHQ questionnaire	Supine, intravaginal + sensor using device developed by the researcher team. First 12 weeks appointment were conducted at the hospital with evaluation after further 12 weeks at home without biofeedback
Hirakawa, et al.	2013	Turkey	RCT	23	23	56.8	23.2	12 weeks	Perineometry, incontinence episode, 1 hour pad test, KHQ and ICIQ-SF questionnaire	Position was not stated, intravaginal + sensor. Initial training at the hospital using FemiScan Clinic System, followed with further 12 weeks of training twice a day each for 8 minutes using FemiScan Home Trainer
Fitz, et al.	2017	Brazil	RCT	30	30	56.3	29	12 weeks	Perineometry, incontinence episode, oxford scale	Supine for the 1st month, sitting for the 2nd month, standing for the 3rd month. intravaginal + sensor using Neurodyn Evolution pressure biofeedback. Twice a week for the first 3 months, each 40 minutes. Followed with further training at home for 6 months.

Abbreviation: BF: Biofeedback; BMI: Body mass index; BPFMT: Biofeedback-assisted pelvic floor muscle training; ICIQ-SF: International consultation on incontinence questionnaire – short form; Kg: Kilogram KHQ: King’s health questionnaire; m: meter; PFM: Pelvic floor muscle; PFMT: Pelvic floor muscle training; RCT: Randomized controlled trial; VAS: Visual analog scale.

Fig. (2). Forest plot of comparative effect between biofeedback PFMT and PFMT only on pelvic muscle floor strength, measured by perineometry (cm H20). SD, standard deviation; IV, inverse variance; CI, confidence interval.

Fig. (3). Forest plot of comparative effect between biofeedback PFMT and PFMT only on incontinence episodes. SD, standard deviation; IV, inverse variance; CI, confidence interval.

In this meta-analysis, higher pelvic muscle strength was shown in patients undergoing BPFMT when compared to PFMT without BF group. In contrast, PFMT only group was associated with improved nighttime micturition. No significant difference was found in incontinence episodes and daytime micturition. These findings contradict the classical belief that stronger pelvic muscle is associated with better incontinence manifestations.

Despite various studies that have been undertaken to address the issue, there is little consensus on the effectiveness of PFMT over BPFMT. Pages et al. [24], Aksac et al. [25] and Schmidt et al. [26] found that the BPFMT group had much higher changes in PFM strength than the PFMT alone group. Some studies, such as Hirakawa et al. [27] and Fitz et al. [28], found no significant difference in PFM strength change in patients between the two groups.

Schmidt et al. [26] hypothesized that BPFMT would develop pelvic muscle floor strength even more because the patient can adjust or improve the training by seeing the intensity and contraction waveform as visual feedback. Another study by Mørkved et al. [29] found that using equipment during training could motivate many women and that it should be considered as a treatment option. Adding biofeedback to pelvic floor muscle training supports pelvic floor exercise, according to Berghmans et al. [30], it is most significant at the beginning of the therapy period. This may justify a considerable improvement in PFM function by boosting exercise performance and treatment motivation and as an easier guide for the patient to learn the exercises correctly [28].

PFM strength improvement following BPFMT or PFMT will consequently increase urethral sphincter strength [31]. The decrease in incontinence episodes and micturition frequency, either daytime or nighttime, are expected from the consequent increase of urethral sphincter strength [32]. Although BPFMT is associated with better PFM strength, in this meta-analysis BPFMT group does not manifest better outcomes in incontinence episodes, daytime micturition, and nighttime micturition.

In comparison to PFMT, Fitz et al. [28] found that BPFMT is related to improved incontinence episodes. However, investigations by Aksac et al. [25] and Hirakawa et al. [27] found that the BPFMT group had similar episodes of incontinence and daytime micturition to the PFMT group. These results are consistent with the findings of this review, which found no significant difference in incontinence episodes or daytime micturition between the BPFMT and PFMT alone groups.

Fig. (4). Forest plot of comparative effect between biofeedback PFMT and PFMT only on daytime micturition. SD, standard deviation; IV, inverse variance; CI, confidence interval

Fig. (5). Forest plot of comparative effect between biofeedback PFMT and PFMT only on nighttime micturition. SD, standard deviation; IV, inverse variance; CI, confidence interval.

We discovered that BF has some advantages of its own, particularly in terms of pelvic muscle strength and function. Through audio-visual feedback, the BF supports patients in isolating and training the right muscle groups, which can be difficult to do without assistance [24]. Biofeedback may be a viable option, particularly for women with low or absent PFM strength or who are unaware of voluntary pelvic floor muscle contraction [27]. Although the use of devices may increase treatment costs; biofeedback provides the patient with an instrument to correctly conduct pelvic floor muscle workouts. Patients with more complicated disease presentations will likely benefit more from the additional information that biofeedback provides.

In summary, the results of all studies revealed heterogeneity in terms of BPFMT's efficacy as a treatment of choice for improving PFM strength. Unfortunately, full-text versions of some literature were not available during the research. Second, there was a scarcity of data on daytime and nighttime micturition. Evaluation variables, such as satisfaction rate, changes in quality of life, and events of recurrence incontinence should be considered in future research on the topic, as these are important clinical features to evaluate once the therapy is completed.

PFMT alone offers a reliable noninvasive exercise in improving incontinence symptoms with current evidence. Despite the significant PFM strength improvement associated with BPFMT, similar incontinence episodes were observed in BPFMT and PFMT. With periodical monitoring by healthcare professionals, PFMT may be done at home to increase cost-effectiveness and the number of hospital visits required throughout the exercise regimen.