Hi there! Well, of course there is a muscle there and there should be some tone there. Some people have a smaller than usual anal opening a relative of mine has a smaller one but he had past surgeries so I suppose it is almost expected. I suppose it depends on how stiff. Is there any pain? If you look in a mirror underneath and behind yourself is it red? Is it hotter than the rest of you? Has there ever been past pain? Do you have hard stools? Have you had any rectal problems? I suppose you could have a professional look for hard growths around it or unusual conditions.