Study on the influence of the type of current and the frequency of impulses used for electrical stimulation on the contraction of pelvic muscles with different fibre content

Abstract

Objective: The aim of this study was to investigate the influence of the type of current and the frequency of impulses of electrical stimulation on the contraction of pelvic muscles with different fibre content. Materials and methods: Electrical stimulation of complete muscles from Wistar rats was performed in vitro with a biphasic square wave current and with a bipolar mid-frequency current at frequencies between 2 and 100 Hz. The parameters of the resulting isometric contraction were determined. Results: The iliococcygeus and pubococcygeus, both with mainly fast-twitch muscle fibres, showed maximal contraction with a biphasic current with square wave pulses at 50 Hz and 60 Hz. The best result in the soleus, with mainly slow-twitch fibres, was with 33 Hz. The mid-frequency current needed a higher intensity to reach lower contraction values but was more effective at the very low frequencies. Conclusions: Current type and frequency of electrical impulses change the electrically induced contraction in pelvic muscles substantially. This should be taken into account when designing and evaluating specific electrical stimulation of pelvic floor muscles aiming at improving either fast contraction or support, or both. From these data, optimal stimulation programmes may be proposed for mainly slow and mainly fast pelvic floor muscles, which need to be evaluated in a clinical setting.