ACTIVITY PATTERNS OF PUBOCOCCYGEAL MUSCLES IN NULLIPAROUS CONTINENT WOMEN

Simultaneous electromyographic (EMG) recordings from the left and righ t pubococcygeal muscles were obtained in 10 continent nulliparous wome n (aged 22-32 years) via wire electrodes inserted percutaneously. Duri ng relaxation, sustained motor unit firing was obtained in 14 and no E MG activity in 4 of the 20 recorded muscle sites. During voluntary squ eeze, stopping urine in midstream and coughing there was always bilate ral recruitment of motor units that was gradual in the recording sites with ongoing EMG activity and brisk in the sites without EMG activity ; the 2 different patterns of activity were called ''tonic'' and ''pha sic'' respectively. Voluntary squeeze led to activation of motor units sustained for 26 to 647 s (median 193.9) with the bladder empty and 2 5 to 600 s (median 198.4) with a full bladder. A marked decrease in on going tonic motor unit activity was seen during the attempt to urinate . Bladder filling caused an increase in tonic activity in 7 females bi laterally and in 1 unilaterally, whereas there was no change in 3 wome n. During the Valsalva manoeuvre, simultaneous motor unit recruitment was seen in all subjects bilaterally with the bladder empty and in all but one with the bladder full: in the latter case the motor unit recr uitment with an empty bladder changed into simultaneous bilateral inhi bition of firing of motor units with a full bladder (both in the supin e and erect position); this pattern changed to bilateral recruitment o f motor units again after bladder emptying. It is important to be fami liar with the normal patterns of activity of the pubococcygeal muscles in continent nulliparous women since the denervation injury caused by childbirth might not only weaken these muscles but also influence the ir behaviour.