Experimental Study No. 1: Directional muscle forces activate anorectal continence and defecation in the female

EMG and radiological data suggest a striated muscle sphincteric mechanism 1 acting during fecal continence control. Though puborectalis and external anal sphincter muscles have been demonstrated to contract during effort,2 the role of the other pelvic floor muscles has not been elucidated. The mechanism of defecation is also poorly understood. According to one description 1 feces enter the anal canal, stimulate stretch receptors and produce the urge to defecate. The internal and external anal sphincters relax, decreasing the pressure within the anus. The rectum contracts and with the assistance of raised intraabdominal pressure (Valsalva) expels the feces. No role is generally assigned for the other pelvic floor muscles. Shafik 3 suggested an active muscular mechanism for anorectal opening and closure: during straining, the puborectalis, acting as the upper part of a triple loop system, contracts to close off the anal canal; during defecation, the puborectalis muscle relaxes, the levator plate contracts, and the “suspensory sling” lifts upwards to open out the anorectal canal prior to evacuation by “rectal detrusor contraction”. This observational study aimed to verify (or not), the directional muscle vectors hypothesized to act during anorectal closure, and also, defaecation. A secondary aim was to identify the hypothesized ligamentous points the vectors act against. Failure to demonstrate these vectors would seriously compromise the Theory.