Frequency analysis of the electromyographic activity in striated pelvic floor muscles: a preliminary report.

A power spectrum of the electromyographic signals in urethral and anal sphincters has been analyzed in 25 patients. Different spectra are observed in each muscle, with higher frequencies in the urethral sphincter. The high frequencies are manifest at short brisk contractions (e.g. cough) and disappear quicly during a sustained voluntary contraction. High frequencies are less pronounced in stress incontinence, but increase in spastic syndromes. The hypothesis is advanced that the proportion of active tonic and phasic motor units determines the efficiency of sphincter reactions.