Adjective to describe one who's often sitting

I think I may come across such a word somewhere. The word starts with letter s. And It looks like a derivative from the word "sit", but I'm not sure. I looked up in the dictionary, only to find something like "situated"; but it doesn't seem to be the adjective word that describes a person who's almost always seated, does it?

Do any one of you know such a word describing a person who's often sitting somewhere, for example, before a desktop computer?

Thanks.