What is tendonitis?
Deep in the shoulder are a group of tendons and muscles called a rotator cuff. They help stabilize the upper arm bone in the shoulder joint and rotate the arm. The biceps tendon is also present in front of the shoulder. When the arm is raised repeatedly over the head, the tendons rub against the underside of the shoulder bone and become irritated. The tendons swell, leaving even less space between tendons and bone. The irritation creates more irritation. It is much like a rope being drawn again and again across a craggy rock.
