The Effectiveness of Pelvic Floor Muscle Exercise with Biofeedback in Women with Urinary Incontinence: A Systematic Review

Abstract

Urinary incontinence affects approximately 200 million people worldwide. The objective of this study was to investigate the effect of pelvic floor muscle (PFM) training with biofeedback (BF) in women with urinary incontinence in comparison to PFM training alone. The primary outcome was PFM strength with secondary outcomes being the severity of incontinence, other PFM parameters, quality of life (QoL), social life, satisfaction and adherence to treatment. Randomized controlled trials (RCTs) published from 2005 to 2023 in PubMed, MEDLINE, Scopus and Google Scholar were searched and evaluated with the PEDro scale. Nine moderate and two high methodological quality RCTs were selected. There was a statistically significant improvement in all parameters. In five studies, muscle strength and the severity of incontinence were statistically better in the BF group compared to the non-BF group. In most studies, no differences were found for QoL and social life between the groups. For adherence to treatment, the results were ambiguous. Τhe remaining variables (endurance, precontraction, function, adherence and satisfaction) had few studies to support the results. There was moderate level evidence that the group utilizing PFM exercises with BF showed significant improvements in the management of urinary incontinence. Concerning muscle strength and the severity of incontinence, findings were inconclusive, as only in some studies the results were statistically better in the BF group compared to the non-BF group.

1. Introduction

Urinary incontinence is a condition which is characterized as the involuntary loss of urine and affects over 200 million people worldwide [1,2]. Even though it can be found in both genders, it has twice as much prevalence in women than in men [3,4]. It affects the muscular and urinary systems as well as quality of life (QoL), including social and sexual life [5,6]. Most patients prefer to seek conservative treatment, whereas fewer may prioritize surgery [7]. One of the conservative methods widely used is pelvic floor muscle (PFM) exercises, which have long been identified as the first line of treatment for urinary incontinence [8]. This has been supported by several studies, which have found that PFM exercises have a significant positive effect in women suffering from urinary incontinence [9,10,11].

Biofeedback (BF) is regularly used as an adjunct to rehabilitation programs used for urinary incontinence [12]. The role of BF is to convert biological signals into comprehensible visual, auditory and/or vibratory ones. Direct information about the condition of the PFMs is provided, permitting patients to “see inside their body” [13,14,15]. Biofeedback devices educate women on how to correctly contract their muscles during the exercise [13,14]. Indeed, researchers of experimental studies [16,17,18,19,20] found improvements in symptoms in women with urinary incontinence after PFM exercises with BF, whereas according to the results of one systematic review [21], PFM exercises with BF were not superior to alternative interventions, such as no training, PFM exercises alone or vaginal electrostimulation.

However, these studies are restricted to women with stress urinary incontinence (SUI) and, as a result, these conclusions cannot be generalized to other types of urinary incontinence (such as urge or mixed urinary incontinence). Furthermore, in Nunes et al.’s (2018) systematic review [21], not all of the included studies compared PFM exercises with BF to PFM exercise without BF, as some group interventions consisted of electrical stimulation, kinesthetic training, etc., while other comparative groups included no training at all. Thus, it is not clear whether PFM exercises with BF are better than isolated PFM exercises (without BF). In addition, outcomes such as the endurance and functionality of the pelvic floor muscles, satisfaction and commitment to the treatment have not been explored [21]. No other systematic review was found that clearly investigated, according to the above, the effectiveness of PFM exercises in combination with BF training for the treatment of urinary incontinence across women. Thus, this area merits further research.

Given the above, urinary incontinence is a condition that negatively affects the muscular and urinary systems as well as the QoL of a large number of women. According to this, we conducted a systematic review investigating the effects of PFM exercises with biofeedback in women with urinary incontinence (stress, mixed and urge) in PFM strength and other muscular variables, QoL and other clinical and functional parameters compared to PFM exercises alone (without BF).

2. Materials and Methods

2.1. Study Design

This is a systematic review consisting of randomized controlled trials (RCTs) evaluating the effects of PFM exercises with BF in women with urinary incontinence compared to PFM exercises alone (without BF). PRISMA (preferred reporting items for systematic reviews and meta-analyses) instructions were followed for the study [22].

2.2. Search Strategy

The databases that were used for the initial search were PubMed, MEDLINE, Scopus and Google Scholar with the use of specific key words, including «urinary incontinence», «stress incontinence», «urge incontinence», «mixed incontinence», «woman», «women», «pelvic floor muscle exercise», «pelvic floor exercises», «pelvic floor muscle training», «Kegel exercise», «biofeedback», «biofeedback training», «muscle strength», «muscle contraction», «pad test», «quality of life», «social interaction», «patients satisfaction», «personal satisfaction», «symptoms severity», «incontinence severity» and «adherence». The key word combinations are shown in Table 1. Randomized controlled studies, published from January 2005 to July 2023, were searched. Furthermore, citations from previous relevant studies were crosschecked and examined for additional related studies.

Table 1. Key words for search strategy.

Νumber	Key Words
1	«urinary incontinence» OR «stress incontinence» OR «urge incontinence» OR «mixed incontinence»
2	«woman» OR «women»
3	«pelvic floor muscle exercise» OR «pelvic floor exercises» OR «pelvic floor muscle training» OR «Kegel exercise»
4	«biofeedback» OR «biofeedback training»
5	«muscle strength» OR «muscle contraction» OR «PAD test», OR «quality of life» OR «social interaction» OR «patients satisfaction» OR «personal satisfaction» OR «symptoms severity» OR «incontinence severity» OR «adherence»
Final search:	Combined search Numbers 1 and 2 and 3 and 4 and 5

2.3. Inclusion and Exclusion Criteria

Specific inclusion and exclusion criteria were set by two independent researchers who agreed in the selection of the studies.

The inclusion criteria were:

• RCTs published in English and in full text;
• The sample of the studies had to include women over 18 years old;
• Women had to have stress urinary incontinence (SUI) or urge urinary incontinence (UUI) or mixed incontinence (MUI) of any severity;
• PFM exercises combined with BF were part of the therapeutic intervention for at least one (experimental) group and were compared with a control group, which followed PFM exercises alone (without BF).

The exclusion criteria were:

• Studies including men;
• Women who in the past had undergone surgery for their incontinence problem;
• The control group followed a placebo or no intervention or any other kind of ‘passive’ intervention (such as booklets and guides);
• PFM exercises with the combination of BF were part of the intervention in both the experimental and control groups.

2.4. Methodological Quality

The methodological quality of the articles was evaluated with the PEDro scale, which is widely used for the evaluation of RCTs and is characterized as a valid and reliable tool [23]. This scale consists of 11 criteria (10 of which are scored). For each criterion, if it was met by the study, a score of 1 was given, and if it the criterion was not met, the article was scored with 0. Scores could range from 0 to 10. Scores between 0 and 3 were characterized as poor in quality, scores between 4 and 6 as moderate and scores between 7 and 10 as high-quality studies. Each study was evaluated independently by two researchers (AEM and EB) and the results were compared. In cases of disagreement, a third assessor (SL) would be involved to solve the disagreement.

2.5. Participants

The included RCTs consisted of adult women who had SUI, UUI or MUI of any severity (mild, moderate or severe) in order to not restrict the generalization of the results. The exclusion criteria involved women with underlying conditions, such as neurological or psychiatric diseases, urinary tract infections, malignancy, etc., which could interfere with the intervention.

2.6. Intervention

The therapeutic intervention consisted of at least one group following PFM exercises combined with BF, whereas the comparative group followed PFM exercises alone (without BF). RCTs involving all types of BF and PFM exercises of any duration, frequency, etc., were all included in the systematic review.

2.7. Outcome Measures

The primary outcome was the PFM strength. Secondary outcomes were the severity of incontinence, other muscular parameters, such as endurance, PFM functionality, QoL, social life, adherence and satisfaction from the intervention. All evaluation tools assessing the aforementioned parameters were considered as acceptable so as not to restrict any RCTs from the systematic review.

3. Results

3.1. Search and Selection

After the initial search, 862 articles published from January 2005 to July 2023 were retrieved. Following the removal of non-RCTs and duplicates, 125 RCTs were selected. From these, 67 RCTs were excluded after a title screening, 26 after an abstract screening and 21 after a full-text screening. Finally, 11 studies were included and evaluated with the PEDro scale [24,25,26,27,28,29,30,31,32,33,34]. The flow chart for the process of the study collection is presented in Figure 1.

Figure 1. Flow chart.

3.2. Methodological Quality

According to the PEDro scale, two studies were considered as being high-quality with a score of 8/10 [26] and 7/10 [34], and the remaining nine as moderate with a score of 5/10 [24,27,31] and 6/10 [25,28,29,30,32,33]. The mean score of these studies was six (Table 2). No differences were found in scoring across the two assessors.

Table 2. Evaluation of studies using PEDro scale.

	PEDro Criteria *										Score
Study	1	2	3	4	5	6	7	8	9	10
1 Schmidt et al. [24]	1	0	1	0	0	1	1	0	0	1	5/10
2 Hirakawa et al. [25]	1	1	1	0	0	0	0	1	1	1	6/10
3 Manonai et al. [26]	1	1	1	0	0	1	1	1	1	1	8/10
4 Ong et al. [27]	1	0	1	0	0	0	1	0	1	1	5/10
5 Özlü et al. [28]	1	0	1	0	0	1	1	0	1	1	6/10
6 Bertotto et al. [29]	1	1	1	0	0	0	1	0	1	1	6/10
7 Fitz et al. [30]	1	1	1	0	0	0	0	1	1	1	6/10
8 Hagen et al. [31]	1	0	1	0	0	0	0	1	1	1	5/10
9 Sigurdardottir et al. [32]	1	0	1	0	0	1	1	0	1	1	6/10
10 Weinstein et al. [33]	1	0	1	0	0	1	0	1	1	1	6/10
11 Kannan et al. [34]	1	0	1	0	0	1	1	1	1	1	7/10
…………											Mean score: 6

* where PEDro criteria 1: “Subjects were randomly allocated to groups”; 2: “Allocation was concealed”; 3: “Group similarity at baseline”; 4: “Blinding of the participants”; 5: “Blinding of the therapists”; 6: “Blinding of the assessors”; 7: “Measures were obtained from more the 85% of the participants”; 8: “Intention to treat analysis”; 9: “Statistical between-group analysis”; 10: “Point measures and measures of variability for at least one key outcome”.

3.3. Participants

The sample in this systematic review included 1165 women in total, with a mean age of 50–60. From these, 62 (5.3%) dropped out for various reasons. All women were at least 18 years old and were suffering from all types of incontinence (SUI, UUI and MUI); in particular, 546 women had SUI and 386 MUI [24,25,26,27,28,29,31,34]. Out of the MUI women, 217 of them were SUI-symptom dominant, 67 were UUI-symptom dominant, 84 had no SUI or UUI dominance in symptoms, whereas the remaining 18 were without a clear presentation. Fitz et al.’s [30] and Weinstein et al.’s [33] studies included both SUI and MUI women (149 in total) without specifying their proportion dominance. In addition, Sigurdardottir’s et al. [32] study included 84 women with all types of incontinence (SUI, MUI or UUI) without, however, any further specifications. The severity of the incontinence of the participants varied from mild up to severe. Most studies (412 women in total) did not report a level of severity [24,25,26,27,30,32,33]. From the remaining studies, 58.7% of the women had mild to moderate incontinence and 41.3% had severe incontinence.

3.4. Biofeedback Mode

In all eleven studies [24,25,26,27,28,29,30,31,32,33,34] there was at least one group that followed PFM exercises with BF, which was compared to a group that followed PFM exercises alone without BF (Table 3). The experimental group (BF with PFM exercises) presented variety, both in the receiving signal and in the application probes. In six studies, they used electromyographic BF (EMG-BF), receiving visual [25,28,29,31,32,34] and acoustic signals [25], and six studies used pressure BF [24,26,27,30,33,34]. Specifically, Kannan et al. [34] developed their own biofeedback device with wearable EMG sensors in the perineal region that displayed the electrical activity during PFM exercises via a mobile device. In addition, besides the EMG group, they had another BF group using a Kegel intravaginal-probe-based device. Additionally, Özlü et al. [28], besides EMG-BF, had a second experimental group that used pressure BF (measuring intravaginal pressure signals). Furthermore, Fitz et al. [30] also used manometric-based pressure BF equipment. Ong et al. [27] used a vibrance Kegel device with a pressure-sensitive body detecting vaginal squeeze pressures that gave vibrational pulses as an active biofeedback on PFM contractions. In Weinstein et al.’s [33] study, the experimental group used an intravaginal insert with arranged accelerometers. This device communicated wirelessly with an application suitable for mobile phones and provided biofeedback by reflecting muscle contractions. In two other studies [24,26], researchers devolved their own biofeedback devices, both receiving pressure signals. Specifically, Schmidt et al. [24] used a microprocessor-controlled unit via a vaginal probe, which stored vaginal pressure waveforms, and Manonai et al. [26] used an air-pressure balloon to measure pressure changes in the vagina giving feedback displayed on a screen.

Table 3. General study characteristics.

Study	Study’s Purpose	Sample (Drop Out)	Intervention	Duration, Frequency and Intensity of Intervention	Outcomes	Evaluation/Reassessment	Results
1. Schmidt et al. [24]	To compare three conservative PFM exercise programs using a new home device	32 (0) A:11 B:10 C:11 Women 30 years old and over SUI or MUI	Discerption of the pelvic musculature and anatomical position A: PFM exercise using a device that showed the exercises B: PFM exercise and BF C: PFM exercise and electrical stimulation After 12 weeks, they continued the exercise without the device for three months	12 weeks Rapid contractions (2 s of contractions and 4s of rest) followed by slow contractions (4 s contraction and 4 s of rest). This was repeated three times with a rest interval	Muscle strength (perineometer) Episodes of urine loss (diaries) Subjective assessment of improvement Quality of life (KHQ) Compliance (ratio between the number of sessions stored and the number of treatment days) and performance (ratio between the number of contractions effectively executed and the total contractions recommended) with treatment	At baseline After the intervention (12 weeks) Reassessment after 3 months	Improvement in muscle strength in all groups (p < 0.05). Time to reach peak force was not significantly different in any of the three groups from baseline (p > 0.05) Urinary incontinence episodes decreased in all groups (p < 0.05) Decrease in subjective perception of the impact of incontinence during the treatment period (p < 0.05) Improvement in KHQ in all groups (p < 0.05) Compliance to treatment was approximately 75% in groups B and C and 84% in group A. Compliance with treatment was not significantly different between groups. Regarding the performance to treatment in group B, this was 81%; in group C, it was 71% and in group A 51% (significant difference between groups A and B)
2. Hirakawa et al. [25]	To investigate the effect of PFM exercises with or without BF on incontinence symptoms and QoL and to assess whether there were other effects on PFM	46 (7) A: 23 (4) B: 23 (3) Japanese women with SUI An episode of urine loss more than once a week	Information about PFM anatomy, muscle localization and function A: PFM exercise with EMG BF (from home) B: Home PFM exercise	12 weeks/twice a day A total of 10 maximal contractions with 5 s hold and 10 s relaxation, followed by 10 rapid maximal contractions with 2 s hold and 4 s relaxation. This was performed twice with a rest interval	Muscle strength (perineometer) Subjective symptoms (ICIQ-SF) Urinary incontinence (voiding diary, 1 h pad test) Quality of life (KHQ) Adherence (exercise diaries)	At baseline After intervention (12 weeks)	Improvement in muscle strength in both groups (p < 0.01). Group A had better results than group B, but without across-group significance (p > 0.05) The frequency of leakage, its quantity and occurrence on a daily basis and the ICIQ-SF score decreased significantly in both groups (p < 0.05) Incontinence episodes reduced in group B (p < 0.05). In group A, they decreased, but not significantly (p > 0.05). The frequency of micturition, the leakage volume and the number of pads did not change significantly in both groups (p > 0.05) Improvement in KHQ (incontinence impact, role limitations, physical limitations, emotions and incontinence severity) in both groups (p < 0.05). Social limitations and personal relationships improved in group A (p < 0.05) Between the groups, there was no statistically significant difference for any parameter (p > 0.05) Adherence was lower in group A (52%) than in B (74.4%)
3. Manonai et al. [26]	To validate the developed for PFM strength evaluation device and to explore if this device in combination with PFM exercise had an effect on symptoms, QoL and PFM strength	61 (2) A: 29 (1) B: 32 (1) Women with SUI An episode of leakage more than one time a week	A: PFM exercise with a sphygmomanometer BF and verbal information about PFM anatomy, muscle localization and function B:PFM exercise	16 weeks, three times/day Maximal contractions for at least 5 s with 10 s relaxation for 5–10 min, followed by 3–5 rapid maximal contractions of 2 s and 4 s relaxation Group A: 15′ biofeedback once	Muscle strength (perineometer) Symptoms severity (patient- based three-point symptom severity scale and the Stamey grading system [35] Muscle contractions (measuring from electromyography abdominal contractions) Quality of life (I-QOL) Adherence (exercise diary)	At baseline Reassessment at 8 weeks (only for muscle strength and contraction) After intervention (16th week)	Improvement in strength in both groups at 8th and 16th weeks (p < 0.05). Between-group difference was not significant (p > 0.05) For symptoms severity, 69.6% from group A and 78.2% from group B stated an improvement (p > 0.05) The percentage of women performing the exercise correctly (without abdominal contractions) was significantly higher in group A than group B at 16 weeks (p < 0.05) I-QOL improved in both groups (p < 0.05). The subscales, of avoidance and limiting behaviors, physiological impacts and social embarrassment improved (p < 0.05). Between-group comparisons were not significant (p > 0.05) Adherence to therapy was lower in group B (56.2%) than group A (68.9%)
4. Ong et al. [27]	To evaluate the effect of PFM exercise with the use of a new vibrance Kegel device for BF and to compare it with PFM exercises alone	40 (3) A: 19 (3) B: 21 Women with SUI	A: PFM exercise and encouragement to perform PFM exercise at home B: PFM exercise with biofeedback and encouragement to perform PFM exercise with BF at home	16 weeks 20′ Endurance: Slow velocity maximal contractions for 3–10 s, followed by 3–10 s relaxation Speed: Quick, moderate strong contractions for 2 s followed by 2 s relaxation 3–5 sets of each type, for 10 contractions in a row or until fatigue	Muscle strength (modified Oxford scale) Total urinary score (APFQ) Subjective cure (unchanged or improvement/and if they consider them self-continent) Social life (APFQ)	At baseline Reassessment at 4 weeks After intervention (16th week)	Improvement in muscle strength in both groups at 16 weeks in comparison to baseline and to the 4th week (p < 0.05). Muscle strength statistically improved in group B compared to group A at 4 and 16 weeks (p < 0.05) Improvement in urinary incontinence in both groups at 16 weeks in comparison to baseline and to the 4th week (p < 0.05). Statistically significantly better results were found in group B compared to group A at the 4th week (p < 0,05). At the 16th week, the difference was not important (p > 0.05) Subjective cure was not statistically different between groups at the 16th week (p < 0.05) There was no statistically significant difference between groups in social life and bothersome score at 4th and 16th weeks (p > 0.05)
5. Özlü et al. [28]	To examine the effectiveness of intravaginal pressure BF and perineal EMG BF in combination with PFM exercise	53 (2) A: 18 (1) B: 17 C: 18 (1) Women over 18 years old Mild and moderate severity SUI (urine loss during specific activities) PFM muscle strength score: 3/5 and over	Information about anatomy and contraction of the muscles A: Home PFM exercise without supervision B: Home PFM exercise and PFM exercise with intravaginal pressure BF with supervision at the hospital C: Home PFM exercise and PFM exercise with EMG perineal BF with supervision at the hospital	8 weeks Home program: First 2 weeks: 5 s contraction with 10 s relaxation, 2 sets of 5 repetitions every day 2–4 weeks: 10 s contraction with 20 s relaxation, 2 sets of 10 repetitions every day 4–8 weeks: 10 s contraction with 20 s relaxation, 3 sets of 10 repetitions every day (lying, siting and standing) Hospital program: 3 times/a week 20 min 40 cycles of 10 s and 20 s relaxation	Muscle strength (perineometer) Severity of incontinence, treatment success (1 h pad test) Quality of life (IIQ-7) Social life (SAI) Satisfaction (Likert scale 1–3) Level of discomfort of application (VAS)	Baseline Reassessment at 4 weeks After intervention (8th week)	Statistically significant improvements in all variables at the 4th and the 8th weeks in all groups (p < 0.05) Between the 4th and 8th weeks, significant improvements in muscle strength, social life and QoL in group B and C (p < 0.05) The 8th week, group B and C had better results from group A (control) concerning the severity of incontinence, muscle strength, social life and satisfaction to therapy (p < 0.05) Success to treatment was more important in groups B and C compared to group A at the 4th and 8th weeks (p < 0.05) Between groups B and C, there were no significant differences in the variables besides the level of discomfort, which was higher in group B at the 4th week (p < 0.05). This level of discomfort decreased the 8th week compared to the 4th week (p < 0.05)
6. Bertotto et al. [29]	To compare PFM exercise to PFM exercise with EMG BF in muscle strength, myoelectric activity, precontraction and QoL	49 (4) A: 16 (1) B: 17 (1) C: 16 (2) Postmenopausal women 50–65 years old with SUI	A: PFM exercise (instructions for home rehabilitation) B:PFM exercise and EMG BF (instructions for home rehabilitation) C: No intervention	4 weeks 20 min, 2 times/a week—8 sessions 1.6–10 s contraction with 6–10 s relaxation, 6–10 rep., 1–2 sets 2. 2 s contraction with 4 s relaxation, 10 rep., 1–3 sets 3. 3–5 s contraction, 6–10 s relaxation time, 8–10 rep., 1–2 sets Home program: 2 times/a week	Muscle strength (modified Oxford scale) Precontraction, initial EMG baseline (μV), final EMG baseline (μV), duration of endurance contraction (s), maximum voluntary contraction (μV), (EMG assessment) Quality of life (ICIQ-SF)	Before intervention After intervention (4th week)	Muscle strength improvement in groups A and B (p < 0.0001). Group A and B had better results from group C (p < 0.001). Group B had better results than group A (p < 0.05) Only in group A was there a significant increase in the initial EMG baseline (μV) (p < 0.05) and also the period of rest from the analysis between the final and initial EMG baseline decreased significantly (p < 0.05). Between groups A and B, there was no important difference (p < 0.05) Both groups A and B had an improvement in precontraction, maximum voluntary contraction and the duration of endurance contraction (p < 0.001). Group B had better results from group A (p < 0.05) QoL improved in groups A and B (p < 0.001). In the between-group comparisons, results were not significant (p > 0.05)
7. Fitz et al. [30]	To examine if outpatient BF with PFM added as home exercise increased the frequency of home exercise after 3 supervised months. Secondly, to extend the evaluation in a long term 9-month follow up	72 (12) A: 35 (5). Additionally, 5 people were lost to follow up B: 37 (7) Additionally, 6 people were lost to follow up Women with SUI or/and MUI	A: PFM exercise with manometric-based BF at the hospital and PFM exercise at home B: PFM exercise at the hospital and at home	3 months (after 3 months, they followed PFM exercise at home for 6 months) 24 sessions, 40 min 2 times/week 1 set of 10 rep Home program: daily 3 sets of 10 rep, 1–10 s contractions depending on the initial assessment followed by twice as much resting time and followed by fast twitch contractions (time of which was evaluated in a similar way)	PFM strength (manometer), PFM function (modified Oxford scale) and vaginal palpation and visual observation for the evaluation of PFM contraction Severity and cure of SUI (modified 20 min pad test) Subjective cure of SUI (by asking them) Quality of life (I-QOL) Adherence (exercise diary) Satisfaction (desire to participate in a different group)	Before intervention After intervention (3 moths) Reassessment at 9 months	In both groups, there was a significant improvement in PFM function and PFM strength at 3 and 9 months (p < 0.005). Between the groups, the difference was not significant (p > 0.05) In both groups, there was a significant reduction in mean episodes of urine loss per week (p < 0.05). Between-group comparisons were not statistically different at 3 and 9 months (p > 0.05) Concerning an objective cure, both groups showed similar improvements at 3 and 9 months. The subjective cure was better in group A at 3 months (three times better from group B, p < 0.05). This difference was not shown at 9 months There was a significant improvement in QoL at 3 months in all domains (avoidance and limiting behavior, psychosocial impacts and social embarrassment) in both groups (p < 0.05), but between-group comparisons were not significant (p > 0.05). This improvement remained in both groups at 9 months Both groups showed great adherence to exercise program (p < 0.05) without significant differences across groups (p > 0.05). Adherence to the hospital was low and between the groups there was no difference (p > 0.05). At 3 months, 85.7% in group A and 81.1% in group B showed adherence. This reduced significantly at 9 moths, whereas 51.4% in group A and 48.6% in group B showed adherence at 9 months (p < 0.005) In both groups, women did not desire to receive a different treatment after asking them at 3 and 9 months (p > 0.05)
8. Hagen et al. [31]	To evaluate the effect of PFM exercise with or without BF	600 (7) A: 300 (5) B: 300 (2) A 6-month PFM assessment A: 154 B: 167 A 6-month questionnaire A: 221 B: 223 A 12-month questionnaire A: 250 B: 254 A 24-month questionnaire A: 230 B: 238 Women with SUI or MUI	A: PFM exercise with EMG BF under supervision and PFM exercise with EMG BF at home B: PFM exercise under superstition and PFM exercise at home	Six sessions (weeks 0,1,3,6,10 and 15) One session lasting 60 m and the rest five lasting 30 m Home program: three sets everyday	Muscle strength-contraction endurance–fatigue (modified Oxford scale) Severity of incontinence (ICIQ-SF) Cure or improvement (ICIQ-SF and PGII) Adherence (exercise diary and questions) Quality of life (ICIQ-SF and EuroQol)	Before intervention, at 6, 12 and 24 months	At 6 months, 13 women (8.5%) in group A and 10 (6%) in group B had maximum contraction strength with no statistically significant difference between groups (p > 0.05). Additionally, there was no difference between groups for contraction endurance and the number of repetitions to muscle fatigue (p > 0.05) There was no significant difference between the groups for ICIQ-SF at any period (p > 0.05) There was no significant difference between the groups for PGII at the 24-month evaluation (p > 0.05). A total of 41% in group A and 38.1% in group B stated that their symptoms were a lot better. Between the groups, the frequency of incontinence was not significantly different (30.3% in group A and 3.4% in group B) (p > 0.05) Quality of life was similar between groups (p > 0.05) There was an improvement in quality of life in both groups but it was not significant Mean scores of adherence were similar between the groups. In total, 67.1% in group A and 64.4% in group B participated in four or more sessions.
9. Sigurdardottir et al. [32]	To examine the effects of individualized physical-therapist-guided PFM exercise on incontinence and related muscle strength and endurance	84 (4) A: 41 (3) B: 43 (1) Women early postpartum (first child) SUI, MUI and UUI	A: PFM exercise with EMG BF under supervision and PFM exercise from home B: Directions on how to contract PFM correctly and encouragement to follow home exercise program	12 sessions, 45–60 min for approximately 4 months 10 close-to-maximum contractions of 7 s and 10s rest in between. For the first two sessions, two sets and after three if it was possible. At the 8th and 9th sessions, they added three rapid contractions at the end of each contraction At home: 10 close-to-maximum contractions, three sets a day and use of the “knack”	Muscle strength (perineometer) Bothersome incontinence (APFQ) Endurance (perineometer) Adherence to therapy (exercise diary)	Before the intervention (9 weeks after childbirth) After intervention (6 months after childbirth) Reassessment at 12 months after childbirth	In group A and group B, there was an improvement in muscle strength without mentioning if it was significant. After intervention, group A had better results from group B (p < 0.005). At reassessment, this difference was significant (p < 0.05) Significantly better improvement in incontinence was shown in group A compared to group B after the intervention (p < 0.05) (57% had incontinence in group A and 82% in group B). In reassessment, this difference was not significant (p > 0.05) (A:76%; B:81%). Bothersome incontinence reduced more in group A than in group B (p = 0.005) (27% had bothersome incontinence in group A and 60% in group B). At reassessment, this difference was not important (A: 45%; B: 41%) Endurance improved in both groups. After intervention, there was a significant difference in endurance between groups in favor of group A (p = 0.01). At reassessment, the difference remained significant (p < 0.005) Adherence was shown at 33%. In group B, 19% exercised three or more times a week. After the intervention until the reassessment, 14% exercised three or more times, whereas in group A, it was 26%
10. Weinstein et al. [33]	To examine whether the use of an intravaginal motion-based digital therapeutic device during PFM exercise was superior to PFM exercise alone in women with SUI	77 (16) A: 37 (8) B: 40 (8) Women with SUI or MUI (predominant SUI)	A: PFM exercise with an intravaginal motion-based digital therapeutic device B: PFM exercise	8 weeks A: 5 rep., 15 s, followed by a 15 s rest. Two times/day for 2.5 min per session B: 10 rep per set. Three times/day	Cure or improvement (PGII) Severity of incontinence (UDI-6, 3-day bladder diary) Quality of life (PFIQ-7) Adherence (self-report of performing 80%—digitally assessed)	Before the intervention Reassessment at 4 weeks After intervention (8th week)	Significant improvement in PGI-I scores in both groups (p < 0.05). There was no significant difference between the groups at 8 weeks (p > 0.05) Significant improvement in UDI-6 scores in both groups at 8 weeks (p < 0.05). Only in group A the minimum important difference was reached from the 4th week. Between the groups, there was no significant difference at 8 weeks (p > 0.05) Median SUI episodes according to the 3-day bladder diary showed improvement was superior in group A compared to group B PFIQ-7 scores showed significant improvement in both groups (p < 0.05). Between groups, group A had significantly better improvements compared to group B (p < 0.05) Self-reported adherence of performing 80% at 4 weeks was 68% in group A and 60% in group B. At 8 weeks, group A and group B showed 97% self-reported adherence. Although, according to the digital assessment, at 4 weeks, group A’s adherence was at 35% and 28% at 8 weeks
11. Kannan et al. [34]	To compare the PFM exercise adherence and effectiveness of the PelviSense devise, the vaginal probe-based device and the PFM without BF in women with SUI	51 (5) A: 17 B: 17 (5) C: 17 Women with SUI	A: PelviSense-assisted PFM exercise B: Vaginal probe-based-assisted PFM exercise C: PFM exercise	Supervised: For 4 weeks, once per week, 45 min, eight contractions for each PFM exercise (total 24 contractions) and each contraction was held for 5–6 s, followed with a 10 s relaxation Unsupervised: After the supervised training, unsupervised home exercise for 24 weeks (with or without the device). At least eight contractions, three times a day, for 5 days/week	Adherence (a tool designed to quantify adherence 0–10-point scale) Severity of incontinence (ICIQ-SF, 1 h pad test) Muscle strength (MOS)	Before the intervention After the supervised intervention 4 weeks Reassessment at 12 weeks At the end of the unsupervised intervention (24 weeks)	After 24 weeks, in group A, 18% showed high adherence (score of 8–10), 71% moderate (score of 3–7) and 11% low (score 0–2). None of the participants in group B and C showed high adherence. In group B, 34% showed moderate adherence and 66% low. In group C, 59% showed moderate adherence and 41% low There was an improvement in ISIQ-SF, 1-pad test and MOS in all of the groups According to the 1 h pad test results, group A had significant better results from group B and group C (p < 0.05) at 24 weeks. Group C had significant better results from group B (p < 0.05) ICIQ-SF scores were significant better in group A compared to groups B and C (p < 0.05) at 24 weeks. Groups B and C showed no significant difference (p > 0.05) MOS showed that muscle strength had significant improvement in group A compared to groups B and C (p < 0.05) at 24 weeks. Between groups B and C, there was no statistically significant difference (p > 0.05)

PFM: pelvic floor muscle; SUI: stress urinary incontinence; MUI: mixed urinary incontinence; BF: biofeedback; KHQ: King’s health questionnaire; QoL: quality of life; EMG: electromyographic; ICIQ-SF: international consultation on incontinence questionnaire—short form; I-QoL: incontinence quality of life; APFQ: Australian pelvic floor questionnaire; VAS: visual analog scale; PGII: patient global impression of improvement; UUI: urge urinary incontinence; UDI-6: urinary distress inventory—short version; PFIQ: pelvic floor impact questionnaire—short form; MOS: modified Oxford scale.

3.5. Intervention

In all eleven studies [24,25,26,27,28,29,30,31,32,33,34], there was at least one group that followed PFM exercises with BF, which was compared to a group that followed PFM exercises alone without BF (Table 3). There was a heterogeny of PFM exercise programs between the studies concerning duration, frequency and repetitions. The duration of the exercise programs in most studies was for either 12 [24,25,30] or 16 weeks [26,27,32], with a frequency of two to three times a week [25,28,29,30]. In most studies, the program consisted of slow maximum contractions up to 10 s long holds each with up to 10 s rest time intervals following each contraction, and 2 s hold rapid contractions. Each fast-contraction set included up to 10 repetitions or until fatigue. In two studies [28,32], the exercise program was progressive as the time of contractions, the repetition and the sets increased as the weeks passed. The non-BF group in all studies followed a PFM exercise protocol, which was similar to the experimental group (without, however, the biofeedback).

3.6. Primary Outcome

PFM strength was evaluated either with a perineometer [24,25,28,30,32] or manually with the modified Oxford scale [27,29,30,31,34]. Ιn one study, the maximum voluntary contraction was also examined with electromyography [29]. Statistically significant improvements in muscle strength were found in both the BF and the non-BF groups (p < 0.05) [24,25,26,27,28,29,30]. In five studies, the BF group had statistically significantly improved results compared to the non-BF group (p < 0.05) [27,28,29,32,34]. It should be noted that, even though Kannan et al. had two BF groups [34], only the EMG BF group yielded a significant difference in PFM strength compared to the non-BF group.

3.7. Secondary Outcomes

3.7.1. Severity of Incontinence

Incontinence in most studies was assessed with questionnaires such as the King’s health questionnaire (KHQ) [25]; international consultation on incontinence questionnaire—short form (ICIQ-SF) [25,31,34]; Australian pelvic floor questionnaire (APFQ) [27,32], patient global impression of improvement (PGII) [31,33] and the urinary distress inventory—short version (UDI-6) [33]. Incontinence was also evaluated with pad tests [25,28,30,34], bladder diaries [24,25,30,33], by asking patients if they had seen an improvement [24] and by using the Stamey grading system, a four-level scale ranging from 0 (continent) to 3 (total incontinence) [26,35]. Significant improvements were found in both the BF and non-BF groups (p < 0.05) [24,25,27,28,30,33].

Between-group comparisons yielded five studies with statistically significant differences (p < 0.05) in favor of the BF group [27,28,30,32,34]. To note, in Kannan’s et al. study [34], only the EMG BF group (not the vaginal-probe-based one) yielded significant differences compared to the non-BF group. For the vaginal-probe-based device (BF) group, according to the ICIQ-SF, there were no differences between the groups in contrast to the 1 h pad test, where the non-BF group had better results. It should be stated that in Weinstein et al.’s [33] study, according to the PGII and the UDI-6, there was no significant difference between the groups in contrast to the 3-day bladder diary, where the results were in favor of the BF group.

3.7.2. Other Muscular Parameters

Besides muscle strength, other muscular parameters were evaluated. Muscle endurance was evaluated with the manometer [32], the modified Oxford scale [31] or electromyography (EMG) [29]. Statistically significant improvements (p < 0.05) in endurance were found in two studies for the BF group compared to the non-BF one [29,32], whereas in one study, the difference was not significant (p > 0.05) [31]. For the evaluation of PFM function, Fitz et al. [30] assessed with the modified Oxford scale, vaginal palpation and a visual examination of women’s ability to conduct PFM contractions. They found that, in both groups, muscle function significantly improved after 3 months. Both groups were then instructed to continue the PFM exercises at home, and a re-evaluation at 9 months revealed that improvements in muscle function were maintained for both groups, although the BF group had better subjective improvements [30].

Furthermore, electromyography was also used to evaluate the PFM precontraction, initial and final EMG baseline activity [29], as well as abdominal wall muscle activity in order to see whether the PFM exercises were isolated or performed together with the abdominal muscles [26]. Statistically significant improvements were also found in precontractions, since they were either generated or enhanced in both the BF and non-BF groups (p < 0.05). Between the groups, the results were statistically better in the BF group (p < 0.05). Concerning the initial EMG baseline values, only the non-BF group revealed a significant increase post-treatment (p < 0.05). Furthermore, after the analysis of the difference between the final and initial EMG baselines, the period of rest significantly reduced in the non-BF group [29]. Finally, it was found that the BF group performed the exercises without abdominal cocontractions (p < 0.05) [26].

3.7.3. Quality of Life

QoL was evaluated with different questionnaires, such as the KHQ [24,25], ICIQ-SF [25,29,31], European quality of life (EuroQol) [31], incontinence impact questionnaire (IIQ-7) [28], incontinence quality of life questionnaire (I-Qol) [30] and the pelvic floor impact questionnaire—short form (PFIQ-7) [33]. In most studies, QoL improved significantly in both the BF and non-BF groups (p < 0.05) without significant differences between them [24,25,26,28,29,30], except for in Weinstein et al.’s [33] study, where the BF group had significantly better results compared to the non-BF one.

3.7.4. Social Life

Social life was examined in five RCTs [25,26,27,28,30]. The same questionnaires regarding QoL were used with the addition of the «social activity index (SAI)» [28] and the APFQ (question 14) [27]. Four studies found substantial improvements in social life (p < 0.05) across both studies’ groups [25,26,28,30]. Only one study, which had two BF groups, showed that both groups had significantly better results than the non-BF one (p < 0.05) [28].

3.7.5. Adherence

Adherence to the exercise intervention was mostly examined with the use of exercise diaries [25,26,30,31,32]. In one study, however, compliance with treatment was calculated as the ratio between the number of attended sessions over the total number of treatments [24]. Additionally, in Kannan et al.’s [34] study, a tool designed to quantify adherence via a 10-point scale was used. The results in two studies showed that adherence to treatment was in favor of the BF group [26,32], in one, it was in favor of the non-BF group [25] and in three, the results were similar across groups [24,30,31]. In Kannan et al.’s [34] study, of the EMG BF group, 18% showed high adherence (score > 8/10), 71% moderate (score of 3–7/10) and 11% low (score < 2). In the vaginal-probe-based BF group, 34% showed moderate adherence and 66% low, and in the non-BF group, 59% showed moderate adherence and 41% low.

3.7.6. Satisfaction from Therapy

Satisfaction from therapy was examined in two studies only. Fitz et al. [30] asked their patients after 3 and 9 months following intervention if they had the desire to follow a different treatment; both groups reported being satisfied and did not wish to have undergone another therapy. Özlü et al. [28] used a three-point Likert scale (not satisfied, no change and satisfied) to assess satisfaction from therapy and showed that both BF groups had significantly better results compared to the non-BF one (p < 0.05).

4. Discussion

This systematic review’s results showed that women after PFM exercises with BF had a statistically significant improvement in muscle strength and other PFM parameters (such as endurance, muscle function and precontraction), severity of incontinence, QoL and social life. These results were mostly based on women with SUI and MUI and, to a lesser extent, on women with UUI. In five studies, out of which four were of moderate-quality [27,28,29,32] and one of high-quality [34], it was shown that PFM exercises with BF had a statistically significant improvement in muscle strength compared to PFM exercises alone. Four out of these five studies included women with SUI [27,28,29,34] and in only one study [32] the sample consisted of women with SUI, MUI and UUI. In the remaining four studies [24,30,31,33], which did not state a significant difference between BF and non-BF groups, the sample consisted of women with SUI or MUI. This could lead to the conclusion that the intervention was more effective in women with SUI for the parameter of PFM strength.

The results of our systematic review were in agreement with another experimental study [36], which found that PFM exercises with BF had a significantly positive impact on PFMs in comparison to a baseline evaluation. In another study [37], it was shown that there was a significant improvement in PFM strength in both BF and non-BF groups. In the systematic review of Nunes et al. [21], PFM exercises with BF were not more effective in terms of muscle strength than other ones (such as isolated PFM exercises, electrostimulation and no training). However, the included studies mostly consisted of low-methodological-quality RCTs, which negatively influenced the results. In contrast, this systematic review consisted mostly of moderate-methodological-quality RCTs [24,25,27,28,29,30,31,32] and two high-quality ones [26,34].

In the study of Ong et al. [27], which was of moderate quality, there was a statistically significant and ‘speedy’ improvement in pelvic floor muscle strength and a reduction in the severity of incontinence in the BF group compared to the non-BF group after the 4-week reassessment. Interestingly, this faster improvement in the BF group after four weeks of intervention was also seen in Weinstein et al.’s study [33]. An explanation for this fast response could be that the biofeedback provided an easy and accurate identification of the PFMs, thus, facilitating the correct contraction of women who were unable to consciously locate or feel the muscles in order to perform the exercises. Interestingly, it was found that approximately 30% of women were not capable of performing isolated pelvic floor contractions after written or verbal guidance [38,39]. Thus, it may be that the BF training during these early stages of PFM rehabilitation may have been beneficial in promoting a faster improvement in muscle tone, better neuromuscular function and also better urethral closure.

One more possible explanation could be that an early improvement gave additional motivation to patients, who were then encouraged to continue the exercises [27]. It is worth noting that positive results from biofeedback may also have been due to the subjects having more interaction with the therapist during the exercise [40]. Such a fast improvement was also shown in the study of Bertortto et al. [29], who also evaluated the participants after 4 weeks of intervention and yielded better results for maximum voluntary contractions and muscle precontractions in the BF group compared to the non-BF one.

Incontinence symptoms improved in most studies. Even though, in some studies, the results were in favor of the BF group [27,28,30,32,34], in other studies, the results were similar between the groups [25,26,30,31,33,34]. It is important to note that in one of the high-quality studies [26], the results between the groups were similar, possibly due to the fact that the intervention group was characterized as a ‘nonintensive’ BF exercise group, since the whole process took 15 min in a single session. As a result, the intervention in both groups was very similar.

In another experimental study, Lee et al. [19] stated that PFM exercises with BF were effective in reducing urine loss and in increasing muscle strength. It has been supported that the increase in muscle strength reduces incontinence symptoms [41]. Bø [42] examined the effectiveness of a PFM exercise program and supported that after the pad test and the urine loss test, there was a correlation between increased strength and decreased urine loss. On the other hand, Sigurdardottir et al. [32] supported that urine loss was not related to muscle strength. It is, therefore, possible that the main clinical benefit in patients with SUI was related to the improvement in the perception of contractions and not necessarily to the improvement in muscle strength. With the application of BF, females improved their body awareness, structural support of the pelvic organs and also reached faster automatic muscle contractions [32]. The biofeedback informed women about their muscle condition, providing them with instant information by giving feedback usually via a screen [43]. By watching physiological data moving towards the right direction, patients felt confidence and satisfaction, thus, enhancing this movement even more [13].

In the systematic review of Nunes et al. [21], the studies mostly found that the volume of urine loss significantly reduced in the BF group compared to the other groups. However, only women with SUI were included compared to this current systematic review, where SUI, MUI and UUI were included. Therefore, the inclusion of only women with SUI could have affected the results because it is known that these women have greater improvements than other types of urinary incontinence [44]. In contrast, one of the RCTs [31] included in the current review mostly consisted of women with MUI and showed that between the BF and non-BF group, there was no significant difference concerning the severity of incontinence. Additionally, Fitz et al. [36] supported that the addition of BF reduced urine loss during exercise.

Concerning muscle endurance, two included studies [29,32] showed that the BF group had significantly better results in comparison to the non-BF group, whereas one showed that there was no significant deference between the BF and non-BF groups [31]. In agreement with the significant improvement were the results from Fitz et al.’s [36] study, who found that PFM exercises with BF improved endurance. In regard to muscle function, in both the BF and non-BF groups, there was a statistically significant improvement (compared to the baseline), but across-group comparison results were similar [30]. In agreement with this was also another study [45]. PFM exercise on a dysfunctional pelvic floor was shown to be attributed to the improvement of structural support, prolonging activation time and enhancing precontractions, which, as a result, might have decreased or prevented urine leakage [46,47]. The purpose of BF is to improve voluntary motor function, promoting neuroplasticity or activating functional neural regeneration mechanisms of the central nervous system by exposing them to new demands. This neuroplasticity process may assist people in controlling and in monitoring muscle activities and movements, enabling them to manipulate these physiological events during the activity [48].

Quality of life had significant improvements in both groups, but between-group comparisons yielded similar results in most of the studies [24,25,26,28,29,30]. For the parameter of social life in most studies, there was a significant improvement in both groups; however, in one study, the results were in favor of the BF group (p < 0.05) [28]. In agreement with these latter results of this systematic review were two other systematic reviews [21,49], which found a statistically important improvement in QoL after PFM exercises with BF. Nunes et al. [21] also showed that the combination of BF with PFM exercises in comparison to alternative interventions (PFM exercises alone, electrostimulation and no training) were not better. On the other hand, UK International Guidelines [50] support that the combination of PFM with BF has had better results concerning QoL (than PFM exercises alone).

The results concerning satisfaction to treatment could not be supported because of the lack of studies (only two moderate-quality studies) examining this outcome. However, in one study [30], patients in both groups were satisfied with the treatment and did not desire to participate in a different group. In the study of Özlü et al. [28], women in the BF groups were more satisfied than women in the non-BF group.

Finally, adherence to treatment was found better in the BF group in two studies [26,32], better in the non-BF group in one [25] and similar between groups in three studies [24,30,31]. In Fitz et al.’s [36] study, it was observed that the frequency of exercise followed at home decreased during the nonsupervised exercise period. This came to an agreement with two other studies [51,52], emphasizing the role of supervision in adherence to exercise programs. In Kannan et al.’s [34] high-quality study, the EMG group showed greater adherence compared to the vaginal probe and non-BF groups. Women in the vaginal probe BF group reported adverse effects (burning and painful urination, discomfort, skin damage near the vaginal region), resulting in the discontinuation of the intervention. Additionally, in the Cochrane review [40], it was supported that adverse events were associated with intravaginal probes leading to the discontinuation of the intervention. This fact may have affected the results.

Others supported that the EMG-BF had an advantage over manometric pressure biofeedback due to the fact that it can accommodate new types of electrodes that are lightweight, more sensitive and designed to stay in place, thus, allowing for a more functional body position for assessment and treatment [43]. In one moderate-quality RCT [28], two BF groups (perineal EMG-BF and intravaginal pressure BF) were included. The results concerning muscle strength, QoL, social life and the severity of incontinence were similar between the groups at both 4 and 8 weeks. It should be noted that the level of discomfort was significantly higher in the intravaginal pressure BF group compared to the EMG-BF group at the 4-week reassessment. In contrast, in Kannan et al.’s high-quality study [34], the EMG-BF group was superior to the vaginal probe BF group concerning muscle strength and the severity of incontinence. However, these results must be interpreted with caution due to the underpowered pilot trial.

The findings of this systematic review add novel contributions to the existing literature. As it has been known, the first-line treatment for urinary incontinence is PFM exercises [8]. Most RCTs included in this review showed that PFM exercises with BF had a significant effect in muscle strength and the severity of incontinence compared to PFM exercises without BF. It is also important to note that besides the significant effect of the combination of PFM exercises with BF on muscle strength and the severity of incontinence, a significantly improvement was also shown in other muscle parameters (such as endurance, precontraction and function), Qol and social life compared to the baseline. As a result, PFM exercises with BF had an important therapeutic effect in women with urinary incontinence. However, it should be noted that these results were based on RCTs that showed heterogeny concerning the type of PFM exercise and the follow-up period.

4.1. Clinical Implications

By incorporating biofeedback into a PFM exercises program, patients showed better coordination and muscle control [53], which was probably most important at the beginning of treatment [54]. Additionally, as mentioned above, BF possibly helped in gaining a faster response to PFM contractions [32]. Furthermore, it was found that the addition of BF in women with very low muscle strength helped to enhance maximum vaginal pressures [29]. The advantage that BF had was that the small contraction amplitude caused by a low muscle force could be visualized. On that account, it is believed that BF should be an option in women with very weak PFM strength. Lastly, BF can be considered as supplementary to the PFM exercise program, allowing patients to observe muscle contractions during exercise, which, in fact, could improve motivation [51,55].

4.2. Limitations and Future Considerations

Limitation of this study were that only English studies were included and most of them were of moderate methodological quality. Additionally, six studies [24,26,27,31,32,33], which relied solely on subjective findings (such as the ICIQ-SF questionnaire) for the evaluation of incontinence, were included. Furthermore, not many RCTs examining the long-term effect, as well as many studies assessing treatment satisfaction, were found. Lastly, the examination of the variables was based on their statistical significance and not on their clinical significance. In addition, the included RCTs showed heterogeny between the type of PFM exercises and follow-up periods. However, this was the case across published papers and clinical practice with PFM exercises. Lastly, a meta-analysis would have been useful, but due to the limited number of studies and the heterogeneity of the outcome measures used, this was not implemented.

In future, more qualitative methodology studies should be carried out examining the satisfaction of therapy. Knowledge whether the intervention gives better satisfaction to the participants would help in the choice of treatment. Additionally, more studies should evaluate the effect in women with UUI, which was the least researched patient subgroup. Finally, it would be useful to investigate the comparison of the effectiveness of different BF types.

5. Conclusions

PFM exercises in combination with biofeedback contributed significantly to all examined muscle parameters, QoL and social life, as well as addressing the severity of incontinence. Concerning muscle strength, five studies showed a significant improvement in the BF group compared to the non-BF group. A similar number of studies showed a significant improvement in favor of the BF group concerning the severity of incontinence. Furthermore, regarding QoL and social life, PFM with BF interventions did not appear to be more effective than PFM exercises alone. For adherence to treatment, the results were ambiguous. Lastly, there were not enough studies to support the results of other PFM parameters and satisfaction to therapy. In conclusion, PFM exercises with BF were proven to be effective for women with urinary incontinence and for the variables of muscle strength and urinary incontinence, shown to be superior to PFM exercises alone. The clinical implications of BF were that it can be used at the beginning of the treatment and in women with very weak or no PFM strength. With the use of BF, patients showed better coordination and muscle control, and the small contraction amplitude caused by muscles with low strength could be visualized. In the future, more studies should emphasize the satisfaction of therapy and investigate which types of BF are better.