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.

J Orthop Sports Phys Ther. 2004; 34(5):228-234. doi:10.2519/jospt.2004.1056

Key Words: dynamometer, elbow, forearm, isometric force, lateral epicondylitis

Study Design: Semiexperimental study. Objective: To investigate the effect of an external wrist extension force on extensor muscle activity during hand gripping in patients with lateral epicondylalgia. Background: Lateral epicondylalgia or ‘‘tennis elbow’’ is a common, often disabling ailment affecting millions of people. An optimal treatment strategy remains to be identified. The use of an external wrist extension force may reduce the extensor muscle activity during gripping in these patients. Methods: Muscle activity of the extensor carpi radialis brevis (ECRB), extensor digitorum communis (EDC), and extensor carpi radialis longus (ECRL) was measured using surface EMG. Subjects gripped at an intensity of 10%, 20%, and 30% of the maximum voluntary contraction (MVC) force with and without the dynamic extensor brace and with and without an applied external wrist extension force of 1%, 2%, and 3% of MVC. Results: At all levels of MVC gripping, the EMG signal of the ECRB and EDC were significantly lower for gripping with than without brace. An extension force of 3% of the MVC force significantly reduced the EMG signal of all muscles in almost all measurement conditions. Conclusions: The results of this study indicate that the dynamic extensor brace as well as the external extension force significantly reduced the EMG signal of the wrist extensor muscles during gripping in patients with lateral epicondylalgia. Based on these results, the dynamic extensor brace could be a promising new intervention for lateral epicondylalgia.

J Orthop Sports Phys Ther. 2006;36(3):170-178. doi:10.2519/jospt.2006.2165

Key Words: electromyography, hand grip, isometric force, tennis elbow