Effect of surface electrical stimulation in a seated position on pelvic oor muscle functions, urinary leakage, and quality of life in women with stress urinary incontinence

Background The aim of this study was to demonstrate the effect of surface electrical stimulation in a seated position (SESSP), as pelvic oor muscle (PFM) training, on PFM functions (time to reach maximal pressure [TRMP], muscle strength, power and endurance), urinary leakage and quality of life in patients with stress urinary incontinence (SUI). Methods Women with SUI were randomized into an SESSP group (n = 18) or control group (n = 18). Quality of life were assessed by the Incontinence Quality of Life Questionnaire (I-QOL). Ultra-short pad test results and PFM functions were measured by perineometer. Changes in the outcomes were assessed before and 8 weeks after SESSP training. Results Thirty-three participants were included in the analysis. There were signicant differences in I-QOL (avoidance and limiting behaviors, psychosocial impacts, social embarrassment and total score) in between (SESSP vs. control group) and within (pre vs. post) group analyses. Signicant increases in PFM strength, power, and endurance, and signicant decreases in the TRMP and pad weight, were observed between (SESSP vs. control group) and within (pre vs. post) groups. Conclusion SESSP in a seated position can be recommended to improve QOL, urinary leakage, and PFM functions in SUI patients. retrospectively


Subjects and design
This was a randomized controlled trial (RCT) with an investigator-blinded parallel randomization (1:1) design (control and SESSP groups). The present study was performed at an obstetrics and gynecology clinic in Seoul, Korea, from August 2018 to November 2018. The sample size was determined a priori (version 3.1.3; University of Trier, Trier, Germany) in a pilot study with three participants in each group (experimental and control groups). The sample size was calculated according to a power of 0.80, alpha level of 0.05 and effect size f of 0.917. The analysis indicated that more than six subjects were required. The women were recruited via advertisements included provided telephone contact information for the study. After the initial contact, visits were scheduled to review the participant suitability according to the inclusion and exclusion criteria of the study, and incontinence severity was checked via the Ingelman-Sundberg scale, as administered during an interview [13].
A total of 36 participants who met the inclusion criteria were allocated to control and SESSP groups through a list of random numbers generated by online randomization software (www.randomization.com) ( Figure 1). Before the study, all procedures were explained to the participants, who then signed informed consent forms approved by the Institutional Review Board (1041849-201806-BM-056-01).

Surface electrical stimulation device
An SESSP device (EasyK7) with three cutaneous electrodes placed in perivaginal (two electrodes) and sacral regions (one electrode) was used to stimulate the PFM and surrounding structures. Three cutaneous electrodes were inserted into the bottom and back of the SESSP device. This allowed for stimulation, via direct contact, of both the perivaginal and sacral regions, and created an electromagnetic eld that stimulated the PFM while the participant sat on the EasyK7 (Figure 2). The initial stimulation amplitude was set by the physical therapist to determine the most comfortable level for each participant. The EasyK7 delivered biphasic, asymmetric impulses of 25 Hz, and controlled the pulse (11 s) and rest (11 s) durations. The mean intensity among all participants was 19.13 ± 5.47 mA (range: 2.5 to 30 mA). Each EasyK7 session was 15 minutes in duration.

Intervention
Participants in the SESSP group were provided with an EasyK7 device, underwent their rst EasyK7 session on site, and were educated on proper device usage, management, and cleaning. Individuals who experienced the SESSP sensation to be aversive were excluded from the study. Participants were instructed to use the device once a day (15-min session) 5 days a week for 8 weeks. All participants participated an EasyK7 session designed to determine the maximum stimulation amplitude that they could tolerate.
The Control group underwent walking for 10 min and restricted PFMT regarding the PFM or abdominal muscle contraction. We gave and educated the EasyK7 to control group as a reward for participating in the experiment after 8 weeks. Both groups were assessed at baseline and after 8 weeks with repeated QOL questionnaires, as well as with ultra-short perineal pad tests and measurements of PFM functions performed using a perineometer.

Outcomes
The outcome of QOL was determined by patient self-assessment. Testers were blinded to the participant's responses to the questionnaires. The I-QOL evaluated incontinence-speci c QOL [15]. The I-QOL consists of three health-related QOL factors: avoidance and limiting behaviors (eight items), psychosocial impact (nine items), and social embarrassment ( ve items); the Korean version was used in this study [16]. The I-QOL has 22 items, each scored using a ve-point scale. Three subscale scores and a total score are calculated. Scores for the 22 items were summed and then adjusted according to a 0-100 scale, with higher scores indicating higher QOL [15].
The objective status of incontinence was indicated by the ultra-short perineal pad test results and PFM power, strength, endurance, and TRMP was measured by perineometer. The ultra-short perineal pad test [17] was performed to assess urinary leakage status, as follows. The participants were allowed to empty their bladder, and any remaining urine was removed using a catheter without anesthetic gel. Then, the bladder was lled with 300 mL sterile water by a gynecologist using a catheter. For the pad test, the participants were provided with a pre-weighed sanitary diaper to place inside their underwear. Participants were instructed to perform a standardized physical activity for 1 minute at a submaximal level: jumping with feet apart and then together, jogging in place with high knees, and jumping up and down; 20 repetitions of each exercise and additional jogging in place were performed until 1 minute had passed [17]. After 10 minutes, the total amount of urine leakage was determined by weighing the pad.
The assessments of PFM functions were performed in a hook-lying position for all participants using a vaginal pressure measurement device. The VVP-3000 perineometer (QLMED Ltd., Gyeonggi-do, Korea), which is a vaginal probe 24 mm in diameter and 115 mm in length with an active surface measurement length of 66 mm, was used. The vaginal probe is connected to a microprocessor with latex tubing, allowing for transmission of pressure readings when the inserted part is compressed by external pressure. The baseline pressure value was recorded in mmHg with no voluntary PFM contraction, and the device was then zeroed.
Participants were asked to contract their PFM and squeeze with maximum effort for 2-3 seconds. They were instructed to pull their PFM in and up as much as possible, and with no use of extra-pelvic muscle contraction. The measurement was taken before the rst contraction and was displayed as a at curve, after the participants had been instructed to relax and given time to slowly breathe in and out [18]. PFM strength was given by the difference between the resting and peak pressure measurement, and reported as the mean of two maximal pressures (in mmHg) [18]. TRMP was measured from the onset of contraction until maximal pressure was reached, and recorded in seconds. Measurement of muscle power required the participants to perform the contraction at maximal pressure as fast as possible. The present study de ned PFM power as PFM strength/TRMP (mmHg/s). Local muscular endurance is the ability of a muscle to sustain sub-maximal or maximal force, assessed as the time over which a person is able to maintain a maximal static or isometric contraction [18]. PFM endurance was measured as the mean contraction pressure for 10 s, during one attempt (mmHg).

Statistical analysis
All statistical analyses were conducted using SPSS software (ver. 18.0; SPSS Inc., Chicago, IL, USA). A p value of 0.05 was used to indicate statistical signi cance. Kolmogorov-Smirnov Z-tests were used to verify that the data were normally distributed. Analysis of covariance (ANCOVA) was used to compare the groups before and after the intervention, with the baseline values used as covariates.
Data are presented as mean ± standard deviation. The effect sizes and con dence interval (CI) for the primary outcomes were calculated to determine the clinical signi cance of the data. An effect size (r) is constrained between 0 (no correlation) and 1 (perfect correlation); in this study, 0 ≤ r < 0.1 was classi ed as no effect, 0.1 ≤ r < 0.3 as a small effect, 0.3 ≤ r < 0.5 as a moderate effect, and r ≥ 0.5 as a large effect.

Results
Thirty-six participants were randomly divided between the SESSP and control groups (n = 18 participants per group). However, two participants in the SESSP group and one in the control group dropped out, citing a lack of time. Therefore, 33 participants completed the interventions and were included in the analysis (Table 1 and Figure 1). Table 2 shows the outcomes, respectively, before and after the intervention (

Discussion
Previous studies have demonstrated the bene ts of PFMT for SUI [7]. Conventional ES devices for PFMT generally use a vaginal or anal electrode, which is invasive and often causes discomfort and injury and leads to low compliance. This can largely be attributed to the fact that the size of the vaginal space limits electrode size and the ability of the user to reach an intensity su cient to elicit PFMT, given the relatively high current density [14]. Thus, the evidence supporting the use of PFMT employing ES for SUI has been equivocal [10,14]. After 8 weeks of SESSP for PFMT, the present study observed improvement in PFM functions, urinary leakage and QOL. SESSP for PFMT over 8 weeks was effective for treating SUI, demonstrating that this is a good option for improving PFM functions, urinary leakage and QOL.
Regarding PFM strength measured by perineometer to assess PFM contraction pressure, a previous study also found an increase in pressure following SESSP [7]. The present study evaluated various PFM functions based on perineometer data. Muscle strength was de ned by Sale as the peak force during a maximal voluntary contraction, while muscle power was de ned as the rate at which mechanical work is performed under a given set of conditions [19]. Muscle endurance is the ability of a muscle to sustain near maximal or maximal force, and is given by the time over which a person is able to maintain a maximal static or isometric contraction [18]. After 8 weeks of SESSP training in the present study, TRMP was signi cantly decreased, and PFM strength, power, and endurance were signi cantly increased. Also, there were signi cant differences in PFM functions between factors (SESSP group vs. control group).
The increases in PFM functions after SESSP training can be explained as follows. First, it may have been due to stimulation of the pudendal nerve by SESSP [20,21]. Because surface electrode in sacral region could stimulate pudendal nerve, thus strengthening its muscle bers, improving electric activation, and increasing proprioception and coordination during pelvic oor contraction [21]. Second, electrode pad in sacral region could restrict pelvic posterior tilt with sacral nutation movement. Sacral counter-nutation movement could more contract PFM compared to sacral nutation movement [22]. Thus, restriction of pelvic posterior tilting might more contract PFM during SESSP. Third, PFM contraction on ES could cause perturbations in myo bers and the extracellular matrix in the case of stimulus overload of the PFM [23]. In addition, the order of motor unit recruitment (from smallest to largest, according to Henneman's size principle) is controversial in ES-evoked muscle contractions; a more reasonable explanation is the random pattern of recruitment of fast-and slow-twitch muscles [23]. PFM is composed of 70% type I slow-twitch bers and 30% type II fast-twitch bers. Thus, ES-evoked contractions could stimulate the PFM according to the random pattern of recruitment of fast-and slow-twitch muscles, and enhance PFM strength and power by increasing the recruitment of fast-twitch muscles, and endurance by increasing the recruitment of slow-twitch muscle. Also, a previous study reported that signi cantly decreased force occurred after 30 seconds of high-frequency (75 Hz) EMS [24]. During this period of high-frequency force fatigue, increased force occurred at a low frequency (20 Hz) [24].
Previous studies have found improvements in urinary leakage, as evaluated by 1-h pad tests in women treated with SESSP, which is consistent with the results of the present study [7,8]. Another study reported similar improvements in 20-min pad tests [4]. In the present study, pad weight decreased signi cantly after 8 weeks of SESSP training and there was a signi cant difference between the SESSP and control groups.
Currently, QOL is considered to be more relevant than quantitative measurements, because it re ects the participants' satisfaction with the treatment. This study found signi cant improvements in avoidance and limiting behaviors, psychosocial impact, social embarrassment, and total I-QOL score, both within (pre vs. post) and between (SESSP group vs. control group) groups. Two previous studies also reported improvements in QOL after SESSP, although this was assessed using the King's Health Questionnaire [7,8].
The decrease in urinary leakage during pad tests and increase in I-QOL after 8 weeks of SESSP training may have been due to increasing PFM functions affecting the proprioception and coordination of pelvic oor contractions during situations that cause SUI [7]. During impact activities, such as running, jumping, and dancing, the PFM power requirement for SUI patients is highest, to decrease urinary leakage [25]. Thus, with changes in PFM power, the mechanism of urethral closure and SUI improves during ultrashort pad tests and impact activities [7,20]. Moreover, the pudendal nerve is an efferent nerve of the external urethral sphincter, so this treatment can increase the pressure of urethral closure, thus improving SUI [7].
The main limitation of this study was the absence of an electromyographic evaluation to verify changes in PFM activation. Another limitation was that we did not utilize ultrasonography to evaluate whether PFM hypertrophy occurs after ES treatment.

Conclusions
SESSP could be considered for SUI patients, to improve QOL, urinary leakage, and PFM functions. SESSP using EasyK7 opens up new possibilities for additional studies, which should include a follow-up session, urodynamic examination, and evaluation of changes in PFM thickness and volume, and in muscle activity (assessed using sonography and electromyography), to con rm the e cacy of SESSP.

Consent to publish
In present study, using consent for publication was obtained from participants to publish potentially identifying details.

Availability of data and materials
The datasets used and/or analyzed during the present study are available from the corresponding author on reasonable request.

Competing Interests
The authors declare that they have no potential con icts of interest with respect to the research, authorship, and publication of this article. The results are presented clearly, honestly, and without fabrication, falsi cation, or inappropriate data manipulation. investigators. Funder about present study was OYK.
Author contribution UJH, OYK made contributions to conception, design and analysis of the study and revised the manuscript. SHJ drafted the manuscript and performed the statistical analysis. MSL, YSK participated in the design of the study and acquisition of data. All authors read and approved the nal manuscript.  Figure 1 Flow diagram of our randomized trial in women with stress urinary incontinence Figure 2 Surface electrical stimulation in a seated position using the EasyK7 device (Alphamedic Co., Ltd.).

Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download. statisticallyanalysis le.xlsx CONSORT2010ChecklistMSWord.doc