I agree with what baybreeze has said. I would like to add too that it could be because of lack of exercise. I know it is difficult to do this when we are in pain, but gentle stretching exercises do help enormously.
No heavy workout type of thing, but just gentle stretching of the affected areas. For instance, if the muscles in your forearm feel this way, hold your wrist and pull gently down - only 5 times each side. This will maybe hurt a little to start but with time, the stretching will "soften" up the forearm and reduce the hardness and stiffness felt there. Do it as often as you feel comfortable with throughout the day.
Just an idea for you to try. It can't do any harm and I have devised quite a few of these gentle stretching exercises which I have passed on to various members of the forum. Not in a medical way of course, just something I helped others with patient to patient.