I have an anal fissure. When I have a bowel movement, I don't feel any pain while I'm having the bowel movement or even a few minutes later. I start to feel pain about 30 minutes after the bowel movement. I have researched this on the internet, and I have discovered that my delayed pain after a bowel movement is a result of my anal sphincter spasming. This delayed pain after a bowel movement as a result of anal sphincter spasms is apparently fairly common with anal fissures. What I don't understand is why would a bowel movement cause the anal sphincter to spasm. When a person has an anal fissure, why does his or her anal sphincter spasm after a bowel movement?