We had a course about it in my engineering master. Called "materials knowledge" if i litterally translate it
You have plastic and elastic reforming of material. The elastic zone is the one wich will revert to its original shape, doing that ALOT can have its wear and tear tho
The plastic zone means you stretched a material beyond its elastic zone, and will permanently alter its shape or form
Like a rubber band that you stretch too far, and will be longer in a rested state, with possibly a few cracks.
We basically learned you shouldnt overstretch the anus or vagina.
Now whilst a vagina is much more elastic and can even recover from considerable agony, like childbirth, overstretching the anus leaves a permanent issue.
According to a former gay classmate, a commen surgery for active homosexuals, is to repair the tightness of the anus, because if it gets to much abuse, the constrictor will be to damaged and you wont be able to hold up your bowl movement