Anyone who has ever had sore muscles may have described it to others as a muscle knot. Of course, this expression is a figure of speech since muscles don’t really tie themselves in knots. To understand how this type of pain happens, a person first needs to know how muscle tissue functions. Every muscle has fibers that run in multiple directions in the body. They are layered one on top of the other. Muscle fibers allow people to do things like bend, dance, and twist. Injury, dehydration, and hours of physical inactivity can cause muscle fibers to lose flexibility and mobility. They stick to each other and feel hard and.