The skeletal muscles in your body are responsible for moving your joints, thus enabling you to walk, jump, lift, and move in many ways. When a muscle contracts, it pulls on a bone to cause this movement. The structure that transmits the force of the muscle contraction to the bone is called a tendon.
Specific tendons are prone to developing tendonitis, a problem where the tendon becomes irritated and inflamed. The usual reason that tendonitis develops is due to deficiencies in blood supply to the tendon. Certain tendons with a "watershed zone" of blood supply are prone to developing tendonitis, these include: