Japan's population is aging rapidly compared to other countries, with the aging rate reached 28.4% in 2020. Under this situation, there is an urgent need to tackle the various health issues that are expected in an aging society. One of the biggest health problems is pelvic floor muscle dysfunctions, such as urinary incontinence (UI). According to an epidemiological survey over 40 years old in Japan, 21.7% of women were reported to have UI symptoms. There has been a lot of discussion about prevention strategies for UI, and pelvic floor muscle training has been noted to be useful to prevent UI. Pelvic floor muscle exercises are recommended to practice at home, but the contraction of the pelvic floor muscle cannot be visualized. Therefore, it is difficult for UI patients to be aware of the contraction sensation by themselves, and to make exercise a habit. These days, there are many ways to help people get a contraction sensation. The previous study that conducted pelvic floor muscle exercise using the cushion to provide vibration stimulation and visual feedback has shown that the muscle activity of the pelvic floor muscles was improved (1). However, the target population of the previous study was men, and the effect on women, who have a higher prevalence of the disease than men, is still unclear. This study is the first study to confirm whether the exercise of the pelvic floor muscle with vibration stimulation and visual feedback using the cushion is effective in increasing muscle activity of the pelvic floor muscle group in women. The hypothesis was that the pelvic floor muscle activity would be higher after the exercise task with the vibration stimulus and visual feedback than after the normal exercise task.

Nine healthy women participated in this study (age: 22.9 ± 0.6). All subjects performed three exercise tasks: control, vibration stimulation, and visual feedback. Each exercise task was a 5-minute exercise of the pelvic floor muscle group; six 10-second sustained contractions of the pelvic floor muscle group were performed, with a 40-second rest period between the 10-second contractions. The participants maintained the seated posture on a cushion (kyuttoburu, Dream Co.) with the hip and knee joints bent at approximately 90 degrees during the exercise task. The vibration terminal is embedded in this cushion. Also, the pressure sensor is designed to contact the pelvic floor muscles, and the participant can get visual feedback by checking the pressure gauge at hand. The maximum voluntary contraction (MVC) of the pelvic floor muscle was measured three times for 5 seconds before and after each exercise task, and the muscle activity of the pelvic floor muscle was recorded by surface electromyography (P-EMG plus, Oisaka Electronic Equipment Ltd.). The electromyogram (EMG) was measured by attaching a blue sensor (P-00-S, Ambu) to the midline of the perineum at two points on the right and left sides to record the muscle activity of the pelvic floor muscle. For comparison of the RMS pre and post the exercise task in each condition, the corresponding t-test was used when normality was followed, and the Wilcoxon signed rank-sum test was used when normality was not followed. Comparison of muscle activity (post/pre) between conditions was performed by Kruskal-Wallis test and Bonferroni as post-test. The effect size (Cohen's d) was calculated for the RMS of pre and post-task exercise in each condition. The level of significance was set at p<0.05.

Table 1 shows the results of RMS pre and post the exercise in each condition. Comparing the muscle activity of the pelvic floor muscle before and after the exercise task, there was a significant increase in muscle activity of 78.28% in the condition with vibration stimulation, 46.42% in the visual feedback condition (p < 0.05), indicating a moderate to high effect size (d = 0.89, 0.81). In the control condition, no significant changes in muscle activity were detected before and after the exercise. Table 2 shows the results of the muscle activity ratio (post/pre). In the comparison between the conditions, the muscle activity ratio was significantly higher in the condition with vibration stimulation than in the control condition (p<0.01). The visual feedback condition also showed a higher muscle activity ratio than the control condition (p<0.05).

This is the first study to show that exercise with vibration stimulation and visual feedback by the cushion can cause an acute increase in muscle activity in the pelvic floor muscle of women. First, we mentioned the increase in muscle activity after exercise with vibration stimulation. The tonic oscillatory reflex induced by vibration stimulation has been reported to be involved in the increase in muscle activity during exercise, and the increase in muscle output after exercise (2). When a vibration stimulation is applied to skeletal muscles, α-motoneurons are excited and muscle contraction is observed due to centrifugal impulses generated by α-motoneurons. At the same time, centrifugal impulses generated by γ-motoneurons cause afferent impulses in the fibers of muscle spindles, which pass through the spinal monosynaptic reflex circuit and induce muscle activity via α-motoneurons. In this study, we suggested that the pelvic floor muscles may have been activated by the same mechanism. Second, it was discussed the reasons for the increase in muscle activity after the exercise using visual feedback. A variety of descending nerve tracts are involved in the voluntary control of muscles. Corticospinal tracts, one of the descending nerve tracts, are related to voluntary control of skeletal muscles such as the pelvic floor muscles, and it has been suggested that motor control is better with visual feedback than without it. A previous study of an exercise intervention in UI patients, using a probe inserted into the vagina to provide visual feedback of pressure during pelvic floor muscle exercises, found that muscle activity in the pelvic floor muscle increased after the exercise intervention (3). In this study, the simple visual feedback by checking the pressure gauge of the cushion helped to exercise the pelvic floor muscle smoothly, and it is inferred that the muscle activity increased after the exercise task with visual feedback compared with the control condition.

The results of this study showed that the exercise interventions in the vibration stimulation and visual feedback conditions immediately increased the muscle activity and muscle activity ratio (post/ pre) of the pelvic floor muscle in healthy women. Exercise intervention for the pelvic floor muscle group using vibration stimulation and visual feedback by the cushion may be one of the effective exercise methods to stimulate the pelvic floor muscle group, which is considered difficult to obtain contraction sensation.

Hirota, A Urabe Y, Komiya M, et al.: Acute effect of pelvic floor muscle with local vibration and visual feedback. Journal of Physical Therapy Science, 2021, 36: 131-136
Cochrane DJ, Loram ID, Stannard SR, et al.: Changes in joint angle, muscle-tendon complex length, muscle contractile tissue displacement, and modulation of EMG activity during  acute whole-body vibration. Muscle Nerve, 2009, 40: 420-429
Burns PA, Pranikoff K, Nochajski TH, et al.: A comparison of effectiveness of biofeedback and pelvic muscle exercise treatment of stress incontinence in older community-dwelling women. J Gerontol, 1993, 48: M167-M174.

Continence 2S2 (2022) 100431
DOI: 10.1016/j.cont.2022.100431