Tight muscles can be caused by MS. I get spasticity off and on, and when I used to have a desk job it was at its worst and was in my neck and spine and shoulders. That was also a stressful job. I still get it in my feet and legs even when I'm relaxing and it can be painful. My toes will go in different directions sometimes and it hurts! If you do long, gentle stretching of your muscles it helps a lot.