Pelvic Floor Muscle Activity During Fast Voluntary Contractions in Continent and Incontinent Women

Aims: Stress urinary incontinence (SUI) has also been attributed to a lower speed of contraction of the pelvic floor muscles (PFM). Therefore, PFM assessment and training implement fast voluntary contractions (FVC). The purpose of the study was to explore FVC regarding feasibility, on-/offset and rate of activity determination, as well as differences between continent (CON) and stress urinary incontinent (SUI) women.

Methods: Fifty women were included and examined by means of PFM EMG during rest, maximum voluntary contractions (MVC), and five FVC. MVC-peak activity was used to normalize EMG-data. On-/offset of muscle activity was determined as mean of rectified rest activity plus 1 standard deviation. Linear regression was calculated for rate of activity from onset to peak, peak to offset, and within 200 ms after both onset and peak. Peak activity and time variables related to onset, peak, and offset were calculated.

Results: On-/offsets were evaluable for 234/222 of 250 FVC by a computer-based algorithm, 16/28 on-/offsets had to be determined manually. There was no significant difference between groups (CON/SUI) regarding FVC peak (92.1/99.3 %MVC), time to peak (514.2/525.6 ms), and increase of activity (182.8/182.1 %MVC/s). The SUI group showed a significantly slower activity decrease (-120.7/-74.4 %MVC/s).

Conclusions: FVC analyses were shown to be feasible. The significant difference observed between the groups did not refer to activity increase but instead to a prolonged relaxation phase in the SUI group. This prompts to reconsider the interpretation of FVC in PFM testing and training.