EXTERNAL EXTENSION FORCE REDUCES ELECTROMYOGRAPHIC ACTIVITY OF THE WRIST EXTENSOR MUSCLES DURING GRIPPING
Niek van Elk, Jan G.M. Kooloos, Mark Massa, Jan A. de Lint, Maria T. E. Hopman · Medicine & Science in Sports & Exercise · 2003
Epicondylitis lateralis is usually caused by repetitive wrist extension that leads to an overuse injury. The current theory is that the process of epicondylitis lateralis begins with an overuse injury that leads to microtearing of the extensor carpi radialis brevis muscle (ECRB) and occasionally the extensor digitorum communis muscle (EDC). Use of an extension force may reduce muscle activity during gripping. PURPOSE 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 in healthy subjects as well as in patients with lateral epicondylitis. METHODS Muscle activity was measured by root mean square values of the surface EMG-signal while gripping at an intensity of 10, 20 and 30% of the maximum voluntary contraction force (MVC) without and with an extension force of 1, 2 and 5% of the MVC. RESULTS Both groups showed that applying an extension force to the palm of the hand reduces EMG activity of the extensor muscles during gripping. The lower EMG activity found in the present study clearly indicates lower muscle activity at the same strength generation during hand-gripping. An interesting aspect is that the muscles with the most significant changes, the ECRB and EDC, are the muscles that are affected in patients with epicondylitis lateralis. CONCLUSION An external extension force reduces ECRB and EDC muscle activity during gripping in healthy controls and patients with lateral epicondylitis. A higher extension force resulted in a greater reduction in muscle activity. The use of this dynamic extension force principle seems to be highly promising in treatment of epicondylitis lateralis.