Muscle and am not really sure if I do or not. My back hurts right around my shoulder blade. but that's not the side I usually lift on. we had a resident almost slide out of his chair last night and we had to lift him in a hurry and he's a very heavy man. We are supposed to lift him with a mechanical lift but he was slid down so far that if we tried to lean him forward he would have fallen out of his chair. And the other lady I work with hasn't learned to lift at the count of three and when I lifted she hadn't lifted yet. And now my upper back hurts. but on my left side and I lifted on my right side. And so I don't know. I just know it feels like I have a knot on my shoulder so to speak.