Pelvic floor muscle (PFM) training has a Level-A evidence rating in treating stress urinary incontinence (SUI). Despite a myriad of teaching methods, between 30% - 70% of women with pelvic floor dysfunction (PFD) cannot perform appropriate contractions. Teaching and learning the appropriate contraction is challenging and may be related to kinesthetic impairments resulting in difficulties executing the motor task of PFM recruitment. More importantly, the capacity to perform PFM contractions may safeguard women from developing PFD. This kinesthetic impairment may be related to a lack of visual stimuli since the PFM are out of sight. Some evidence suggests neuromuscular electrical stimulation (NMES) may be better than no treatment for SUI. However, intravaginal electrical stimulation is the least effective compared to interventions that promote PFM contraction. Limitations as to its efficacy may relate to the size of the stimulation surface area, which is limited by the vaginal space, the maximum tolerable intensity, and the associated current density. This study aimed to determine if NMES delivered externally in a pair of shorts (INNOVO) with a large surface area of integrated novel conductive ink electrodes provided a sufficient sensorimotor stimulus to enhance volitional PFM function in healthy women who could not contract their PFM.

Ten healthy women aged 23 – 58 (mean 35 years) with a mean BMI of 25.1 kg/m2 participated. Inclusion criteria included women 18 or older who could not perform an appropriate PFM contraction assessed via transabdominal ultrasound (TAUS) in supine and standing positions. An appropriate contraction was where the bladder base (BBD) was observed to move cranially when observed with transabdominal ultrasound imaging (TAUS) with the transducer oriented in a transverse plane.  Exclusion criteria included those who could perform an appropriate PFM contraction, had a confirmed pregnancy, neurological disease, pelvic organ prolapse, lumbopelvic surgery, recurrent urinary tract infections, and cardiac pacemaker. A bladder-filling protocol facilitated the delineation of structures during TAUS of BBD in millimeters (mm) under five conditions: pre-NMES volitional contractions in supine and standing, INNOVO NMES in standing, and post-NMES volitional contractions in supine and standing with at least a 5-minute washout period between INNOVO and post-NMES conditions. INNOVO shorts consist of eight integrated electrodes, with a cumulative stimulating surface area of 1200cm2 with a maximum current density of 0.189 mA/cm2. The electrodes are positioned bilaterally around the pelvis, anterior and posterior thighs. INNOVO uses patented multipath stimulation delivered via a pulsed, symmetrical, rectangular biphasic waveform at 50Hz. A pulse duration of 620µs was delivered for 5 minutes (on:off time of 5:5secs), resulting in 30 elicited PFM contractions. Participants were blinded to TAUS and verbally cued to perform volitional PFM contractions pre and post-INNOVO NMES. No verbal cues were given during INNOVO NMES, delivered at each participant's maximum tolerable amplitude (mA) to elicit a PFM contraction confirmed by a cranial displacement of the BBD observed with TAUS

A one-way repeated measures analysis of variance (ANOVA) revealed a statistically significant difference over time and large effect F (4,32=14.219), p<.001, partial η2= .64. Post-hoc analysis with a Bonferroni adjustment revealed INNOVO NMES contraction with mean BBD = 8.6mm (95% CI, 5.6 - 11.6) statistically significantly increased from baseline assessment in supine (p=.002) and standing (p=.002) where no cranial BBD was evident via TAUS. While post-NMES volitional contractions statistically significantly increased from baseline in supine with mean BBD=5.05mm (95% CI, 2.1- 8.1) p=.039 and standing with mean BBD=6.1mm (95% CI, 2.4 - 9.8) p=.049. There was no difference between INNOVO NMES and post-INNOVO contractions for supine (p=.44) or standing (p=1.0) positions. One participant was unable to contract her PFM post-INNOVO use.

The findings of this proof of concept study suggest that a 5-minute bout using INNOVO NMES provided a significant sensorimotor stimulus that facilitated awareness of pelvic floor function and improved the ability to contract the PFM in supine and standing. All but one individual could contract their PFM post-NMES.  This may be related to the individual’s age, gravidity,  having the highest BMI and tolerating a relatively lower amplitude (mA/min) than the other participants, which may not have provided a sufficient phase charge to elicit a contraction. High NMES amplitudes elicit a motor response and induce a cortical facilitation effect. In contrast, low amplitudes are associated with a cortical inhibitory effect, thus showing an amplitude-based dose effect. Studies report that NMES-elicited contractions recruit proprioceptive receptors by stimulating muscle spindles and Golgi tendon organs that send afferent information to the somatosensory cortex. Muscle spindles and cutaneous receptors also play a significant role in kinesthesia, and sensorimotor afferents facilitate changes in motor control. Consequently, the presence or lack of a contraction directly impacts the somatosensory cortex and, ultimately, cortical excitability as determined by motor-evoked potentials (MEP).

A 5-minute bout of INNOVO elicited contractions that significantly improved PFM function in women who initially could not contract their PFM in supine or standing. Since increased strength cannot explain this improvement, it is plausible that INNOVO stimulated many proprioceptive and kinesthetic receptors in addition to sensory afferents, which led to an immediate change in motor response. This finding should not be surprising since numerous studies have shown that NMES can induce neural plasticity. This pilot study will inform a randomized controlled trial to determine the longevity of effects on PFM function and symptoms associated with SUI.

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