When patients go to their rheumatologist or orthopedist with aches or pains, they are often told they have tendonitis. The term tendonitis means inflammation of a tendon. Tendons are tough fibrous cords of tissue that connect muscles to bones. When muscles contract (tighten) the tendon attachment makes the bone the tendon is attached to move in the direction of the contracted muscle. When the muscle relaxes the bone moves back to its original position.
To picture this, imagine tying a rope (the tendon) to a piece of wood that is lying on the floor. When you pull on the rope (contract the muscle), the piece of wood moves up into the air. When you let go (muscle relaxation) the piece of wood drops back to the floor.
Most tendons move inside a sheath that is lined with synovial tissue (the same kind of tissue that lines the inside of joints) and which contains a small amount of lubricating fluid that allows the tendon to glide easily.
Since tendons are made of relatively inelastic tissue, they do not stretch. While this property is good for movement, it makes tendons susceptible to injury. Tendonitis can also occur from overuse. When this situation occurs, and the synovial lining.