Anorectal Angle
Some authors believe that the anorectal angle (ARA), the angle formed by the junction of the rectum with the anus, is "one of the most important contributions to anal continence"; its normal value at rest is 90 degrees.
According to a 1996 article in the Townsend Letter for Doctors and Patients,
In a classic paper, Tagart (1966) measured the anorectal angle in various postures, finding that the angle is partially straightened out when squatting. He argued that squatting thereby reduced the pressure required for defecation and recommended a hips-flexed position for defecation to help treat constipation and prevent haemorrhoids. —In persons with anismus the anorectal angle during attempted defecation typically is abnormal. This is due to abnormal movement of the puborectalis muscle, a hallmark of anismus.
Read more about this topic: Human Defecation Postures
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