Activation of the Striated Urethral Sphincter to Maintain Continence During Dynamic Tasks in Healthy Men

Aims: Function of the striated urethral sphincter (SUS) in men is debated. Current evidence is limited to electromyographic (EMG) recordings made with concentric needle electrodes in supine. Understanding of SUS function requires investigation of SUS EMG activity using new recording techniques in dynamic tasks. The aim of this study was to evaluate timing and amplitude of SUS EMG at rest and during dynamic tasks that challenge continence by increasing intra-abdominal pressure (IAP).

Methods: Investigative study of five healthy men aged 25-39 years. Measurements included SUS, anal sphincter (AS), and transversus abdominus (TrA) EMG, and IAP (recorded with a nasogastric pressure catheter). Participants performed four tasks that challenged postural control in standing (single and repetitive arm movement, stepping and load catching).

Results: IAP amplitude and SUS activity were linearly correlated during repetitive arm movement (R(2): 0.67-0.88). During stepping SUS EMG onset preceded the IAP increase, but followed it with rapid arm movements. When the trunk was loaded unpredictably onset of SUS generally followed the increase in IAP. The modest sample size meant only younger men were tested. Future studies might investigate healthy older men or those with certain pathologies.

Conclusions: Data show that SUS activity increases proportionally with IAP. This provided evidence that SUS contributes to continence when IAP is increased, and that postural control of the trunk involves activation of this muscle.