Sitting with your back straight at 90° with your thighs is very common while sitting in “Western-style” flush toilets. But this is the wrong posture. The passage for defecation becomes narrow due to the pull of puborectalis muscle. It is a muscle band that rings around the end of the colon. When the thighs and hips make a 90° angle, this muscle is taut and doesn’t allow the colon to open properly. The correct way to sit is to lean forward so that your spine is at an angle of around 35° with respect to your thighs.