The application of an external wrist extension force reduces electromyographic activity of wrist extensor muscles during gripping.

STUDY DESIGN Experimental repeated-measures study. OBJECTIVE To investigate the effect of different extension forces applied to the palm of the hand on electromyographic (EMG) activity of the wrist extensor muscles during hand gripping. BACKGROUND Lateral epicondylitis is usually caused by repetitive wrist extension that leads to an overuse injury. The current theory is that the process of lateral epicondylitis begins with an overuse injury that leads to microtearing of the extensor carpi radialis brevis muscle and occasionally the extensor digitorum communis muscle. Use of an external wrist extension force might reduce muscle activity during gripping. METHODS Muscle activity was measured using surface EMG while subjects gripped at an intensity of 10%, 20%, and 30% of the maximum voluntary contraction force without, and with, an applied external wrist extension force of 1%, 2%, and 3% of maximum voluntary contraction. RESULTS Applying an extension force to the palm of the hand reduced EMG activity of the extensor muscles at the same strength generation during hand gripping. The muscles with the most significant reduction in EMG level, the extensor carpi radialis brevis and extensor digitorum communis, are those muscles that are most often involved with lateral epicondylitis. CONCLUSIONS This study shows that an external extension force reduces EMG activity of the wrist extensor muscles during gripping in healthy volunteers. As the extension force increased, a greater reduction in muscle activity was noted.