Tennis Elbow is typically caused by the motion of a tennis downstroke. The muscle of the forearm (Extensor Carpi Radialis Brevis) becomes weakened from overuse. Small tears can form in the tendon fibres that attach the muscle to the elbow, leading to pain and inflammation. As the elbow bends and straightens, the muscle rubs against bony bumps in the forearm, which can cause gradual wear and tear of the muscle over time.
Tennis Elbow can happen to anyone who uses their forearm muscle regularly. It is common in painters, plumbers, carpenters, cooks and butchers.