The temporal relationship between activity of the pelvic floor muscles and motion of selected urogenital landmarks in healthy nulliparous women.

Aims: The purpose of this study was to investigate the relationship between pelvic floor muscle (PFM) electromyographic (EMG) activation and urogenital landmark motion measured using 2D transperineal ultrasound (US) imaging.

Methods: Eight healthy, nulliparous women performed maximum voluntary PFM contractions while EMG and transperineal US images were acquired simultaneously. Changes in the levator plate length (LPL), bladder neck (BN) position and urethral position were determined by visual inspection. The relative timing of EMG onset and the onset of landmark motion, and the correlation coefficients between EMG activation and landmark motion were computed. Comparisons between the correlation coefficients and onset latencies of each landmark motion were made using one-way analysis of variance models.

Results: Despite generally good reliability metrics for the onset of EMG and the onset of landmark motion, the relative timing of EMG onset and the onset of landmark motion demonstrated no systematic patterns of activation onset. That said, the overall motion of the different urogenital landmarks throughout the MVC task was highly correlated with the PFM EMG data; correlation coefficients were generally good (>0.90) and highly significant (p < .001). The correlation between PFM EMG and LPL motion was significantly better than the correlation between PFM EMG and motion of the other landmarks. The relevance of one outlier is discussed.

Conclusions: The motion of all urogenital landmarks seen on US imaging is highly correlated with PFM EMG activation during maximum voluntary PFM contractions and may therefore be of value in the context of biofeedback training to infer that PFM activation has occurred. The motion of the BN, however, may require more cautious interpretation than the reduction of LPL. The timing of the onset of urogenital landmark motion on transperineal US imaging does not precede nor follow the timing of PFM activation, while the high variance of relative onset timing makes the onset of landmark motion of questionable value when training or evaluating co-ordination or motor control.