Disorders of defecation are very common and the process of defecation remains poorly described. This results in a limited approach to treatment of patients, with limited success. This study will simultaneously measure multiple components of the process of defecation - the abdominal wall and perineal muscle activity, the pressure within the rectum and in the anal canal and the change in shape of the anorectal region of the colon, in order to develop a biomechanical model which can describe the normal and abnormal defecatory process. It is anticipated that, by understanding the process in these terms will allow a new approach to categorizing and describing defecation problems which in turn will lead to more specific approaches of treatment which will be tailored to individual patients. These parameters will compared in volunteers with no defecatory disorders and patients with defecatory disorders who are being referred for defecography as part of their clinical evaluation.