Anal fitness? And, from a pictureless?
Google on hemorrhoids. webmd.com is a good resource. As is Mayo Clinic.
If you are having anal fissures that means you're trying to put something to big into your ass. If that's happening well...sooner or later you'll have a mess, or have enough scar tissue your ass will get bigger. You can go to the doctor and have them to an anal dilation, or stick a big dildo up your behind and leave it. That will stretch you out, to a degree, but, if you are getting tears, well, at some point, you need to let common sense prevail and not do that.