Yes. I have tmj and I do have a more predominant scm muscle. I don't think, though, they are exactly related (although I am sure clenching/teeth grinding is not helping). The scm is most likely "enlarged" because of muscle tightness & tension (bad posture, cradling the phone, etc). Also remember, our muscles are not 100% exactly the same, so that may be the way that it is. I see a medical massotherapist for neck/shoulder issues (mostly stress & posture related - 2 drs recommended it to me). Nothing is wrong with my scm. I will say it is extremely tight and the massage therapy is very painful there, and my masso did tell me the dizziness/lightheaded feeling comes from a tight scm muscle. although strecthes help, you may need a medical massotherapist. It totally helped with my neck fears (i too worried about something growing in my neck from the tightness and pressure - but turns out it was all muscle tension). Hope this helps.