Over the last year and a half both of my hands will "lock-up" in a clenched position.( usually during work with my hands, i.e. painting or using a hammer) They aren't painful, I just can't use them, they will not move. I have to push each finger back and not use them for a time until they will work again. If I try to go back to work they will lock up again, this time becoming a little more painful. Can any one give me an idea of whats going on?