The knee is a hinge joint and because of this, its primary motions are flexion and extension. Muscles are attached at specific points around the knee joint and the location of these attachments dictate the action of the muscle.
Muscle tissues that attach to bone are called tendons. Repeated use of a muscle can result in an overuse injury known more commonly as tendonitis.
The iliotibial band (ITB) is an extension of the gluteus muscle and the tensor fascia latae. These two tissues taper downwards along the outer side of the thigh and form a dense tissue (ITB) that attaches to the outer portion of the knee joint.
An irritation of the iliotibial band at the point where it attaches to the outer knee (lateral epicondyle) is called iliotibial band friction syndrome. For many, this means pain while sitting and constant irritation when active.