Modified muscle activity in LE

L. J. Heales, B. Vicenzino, D. A. MacDonald, P. W. Hodges

Lateral epicondylalgia (LE) is associated with a reduced wrist extensor muscle activity and altered biomechanics. This study compared the coordination between forearm muscles during gripping in individuals with LE and pain-free controls. Intramuscular electrodes recorded myoelectric activity from extensor carpi radialis brevis/longus (ECRB/ECRL), extensor digitorum communis (EDC), flexor digitorum superficialis/profundus (FDS/FDP), and flexor carpi radialis (FCR), bilaterally, in 15 participants with unilateral LE and 15 pain-free controls. Participants performed a gripping task at 20% maximum force in four arm positions. The contribution of each muscle was expressed as a proportion of the summed electromyography of all muscles. In individuals with LE, ECRB contributed less to total electromyography in the symptomatic arm but not the asymptomatic arm than pain-free controls. The contribution of EDC and FDP to total electromyography was greater in both the symptomatic and asymptomatic arm of the LE group, than pain-free controls. No other differences were observed between groups. Subtle differences in muscle activation were present with differing arm positions. These findings indicate forearm muscle activity is modified in LE. It is unknown whether this is cause or effect. Changes in the asymptomatic side may imply involvement of central mechanisms.