An estimated 30 - 50% of women cannot volitionally recruit their pelvic floor muscles (PFM). Proprioception is fundamental to motor learning, and sensorimotor afferents may facilitate changes in motor control. Neuromuscular electrical stimulation (NMES) is used clinically as an adjuvant intervention to facilitate pelvic floor muscle (PFM) contractions.  Neural imaging shows that NMES contractions activate similar cortical and subcortical structures to volitional ones. Consequently, these NMES elicited contractions may enhance proprioception and PFM function.  This study aimed to determine if NMES delivered in a pair of shorts (INNOVO) provided a proprioceptive stimulus to enhance PFM function in healthy women.

Ten healthy continent women aged 23 – 57 years gave written informed consent and participated in this study. Inclusion criteria included women 18 years or older and the ability to perform a PFM contraction. Exclusion criteria included 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 transabdominal ultrasound imaging (TAUS).  The magnitude of bladder base displacement (BBD) was measured in centimeters (cm) under three conditions in standing: pre-NMES volitional contractions, INNOVO NMES contractions, and post-NMES volitional contractions with at least a 5-minute washout period between conditions.   INNOVO shorts consist of eight embedded 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 5sec:5sec), resulting in 30 elicited PFM contractions.   Participants were blinded to ultrasound imaging and verbally cued to perform volitional PFM contractions pre and post-INNOVO NMES. No verbal cues were given during INNOVO NMES, which was 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 significant difference over time and large effect F (1,9=29.57), p<.001, partial η2= .77. Post-hoc analysis with a Bonferroni adjustment revealed INNOVO NMES contraction with BBD = 1.31cm statistically significantly increased from baseline contraction with BBD = 0.42cm (95% CI, 0.47-1.30), p<.001 and post-NMES volitional contraction with BBD= 1.1cm (95% CI, 0.07-0.53), p=.011, while post-NMES volitional contraction with BBD= 1.1cm statistically significantly increased (95% CI, 0.27-0.90), p=.001 from baseline volitional contraction with BBD= 0.42cm.

The findings of this proof of concept study suggest that a 5-minute bout using INNOVO NMES provided a proprioceptive sensorimotor stimulus that significantly enhanced pelvic floor function.  All PFM contractions post-NMES showed a greater magnitude of BBD when compared to baseline.  Studies report that NMES elicited muscle contraction plays a role in proprioception by stimulating muscle spindles and Golgi tendon organs that send afferent information to the somatosensory cortex.  High NMES amplitudes, which elicit a motor response, induce a cortical facilitation effect. In contrast, low amplitudes are associated with a cortical inhibitory effect, thus showing an amplitude-based dose effect.  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 brisk INNOVO elicited contractions significantly improved PFM function compared to pre-INNOVO function in healthy continent women. Since this improvement cannot be explained by increased strength, it is plausible that INNOVO stimulated a large number of proprioceptive receptors and sensory afferents, which led to the immediate change in motor response. This finding should not be a surprise since numerous studies have shown that NMES can induce neural plasticity.  Future studies should look at the longevity of these effects and their impact on pelvic floor function in those who cannot volitionally recruit their PFM.

Jiang SL, Wang Z, Yi W, He F, Qi H, Ming D. Current Change Rate Influences Sensorimotor Cortical Excitability During Neuromuscular Electrical Stimulation. Front Hum Neurosci. 2019; (13):152.  doi: 10.3389/fnhum.2019.00152
Insausti-Delgado A, López-Larraz E, Omedes J, Ramos-Murguialday A. Intensity and Dose of Neuromuscular Electrical Stimulation Influence Sensorimotor Cortical Excitability. Front Neurosci. 2021;(14):593360. doi: 10.3389/fnins.2020.59336
Carson RG, Buick AR. Neuromuscular electrical stimulation-promoted plasticity of the human brain. J Physiol. 2021;599(9):2375-2399. doi: 10.1113/JP278298

Continence 2S2 (2022) 100199
DOI: 10.1016/j.cont.2022.100199