The aims of the study were to characterize the interference pattern in perineal muscles in healthy subjects with the use of quantitative EMG techniques, to evaluate if prostatic surgery had any effect on the interference pattern and furthermore to examine the interference pattern in the perineal muscles in patients suffering from urinary or anal incontinence.

The interference pattern in the perineal muscles was examined with a computerized analysis, the Turns and Amplitude (T/A) analysis, and the innervation pattern of the muscles was examined with single fiber electromyography measuring the fiber density. Reference values were collected from 30 normal subjects. The patient material consisted of 20 males subjected to transurethral prostatectomy (TUR-P), 10 males who underwent radical retropubic prostatectomy (RRP), 20 patients suffering from anal incontinence and 24 women withurinary incontinence.

T/A analysis of the interference pattern in the perineal muscles in normal subjects showed a significant increase in number of turns/sec and mean amplitude correlating to increasing force but no age-related changes.

TUR-P and RRP did effect the innervation of the distal urethral sphincter muscle as shown by increased fiber density indicating a peripheral nerve lesion. T/A analysis did not shown any increased activation of the distal urethral sphincter as a compensation for the loss in bladder neck sphincter function but rather signs of decreasedcentral activation.

Patients with idiopathic faecal incontinence showed signs of impaired innervation of the external anal sphincter muscle. A decreased interference pattern at maximal contraction indicated a reduced central activation of perineal muscles, in particular for patients with partial rupture of the external anal sphincter muscle. The reduced central activation could play a role for the aetiology of faecal incontinence.

Patients with urinary stress incontinence also showed signs of impaired innervation of the external anal sphincter muscle as well as reduced interference pattern at maximal contraction and during continuous recording of the EMG activity during cystometry. A reduced central activation of the motor units was predicted as one factor involved in the aetiology.