Tennis elbow is pain on the outside of the elbow, which radiates into the forearm, increasing in intensity on gripping. This condition, known medically as Lateral Epicondylitis, is not exclusive to tennis players!
There are 2 main groups of muscles in the forearm, one to extend the wrist and another group to flex the wrist. Imagine all the muscles which extend the wrist converging into one common tendon, like a bunch of bananas, and inserting into a small bony prominence above the elbow. Unfortunately, if these muscles become very tight, the tendon is pulled taut, becoming inflamed and irritating the bony insertion point. This occurs when the muscle is overused and not regularly stretched. Commonly associated with Repetitive Strain Injury (R.S.I.), this is a chronic and painful condition, which can cause weakness.
Treatment involves resolving the inflammation and spasm of the muscles, as well as discovering what activity is causing the symptoms. Advice on stretching and altering the aggravating activity is essential to a full recovery.