A lot of tendons, which are connective tissues that anchor muscles to bones, come into play when you're running. Tendons in your hips, knees, ankles and feet are all potential places where a runner might suffer from tendinitis.
Tendinitis occurs when the tendon becomes inflamed or damaged from overuse. Tennis elbow, for example, is a form of tendinitis. Runners can have particular difficulty with Achilles' tendinitis.
While tendinitis treatments resemble that of other sports injuries (R.I.C.E.), this therapy method can be troublesome because the pain comes on gradually over the course of days or weeks. The runner may not realize the problem is tendinitis until it's become quite severe -- visibly swollen, with the joint almost unusable due to the pain. It's easier to treat when caught early, so caution is the best way to avoid making it worse.