Electromyographic and cinematographic analysis of elbow function in tennis players with lateral epicondylitis.

Lateral epicondylitis occurs frequently in tennis players and appears to be caused by tears in the extensor aponeurosis. The purpose of this study was to compare the electromyographic activities of 5 muscles in players with lateral epicondylitis with those of injury-free players during the single-handed backhand tennis stroke. Finewire electrodes were placed into the extensor digitorum communis, extensor carpi radialis longus and brevis, pronator teres, and flexor carpi radialis muscles in competitive tennis players; 8 players had lateral epicondylitis and 14 had normal upper extremities. The backhand stroke then was recorded on high-speed film and synchronized with the electromyographic signal. The injured players had significantly greater activity for the wrist extensors and pronator teres muscles during ball impact and early follow-through. This activity increase may have been caused by the abnormal mechanics evident on film, including a "leading elbow," wrist extension and an open racquet face near the time of ball impact, and ball contact in the lower half of the strings. These mechanics not only result in a lower level of play but also leave the wrist extensors and the pronator teres muscles vulnerable to injury. This is the first study that documents increased activity in muscles that have been previously injured.