Tennis elbow is a pain focused on the outside of the arm, where your forearm meets your elbow.
It’s related to a muscle and tendons in your forearm. Tendons connect your muscles to your bones. When you constantly use your arm in a repetitive motion, the tendons at the elbow end of a certain muscle -- the extensor carpi radialis brevis (ECRB) muscle --- may develop small tears.
The tears lead to inflammation and may put stress on the rest of your arm, making it painful to lift and grip things. Left untreated, it can become chronic.
Tennis elbow affects up to 3% of the population, particularly adults between 30 and 50 years of age -- but fewer than 5% of cases are actually linked to tennis.