Testing apparatus and experimental procedure for position specific normalization of electromyographic measurements of distal upper extremity musculature

Objective. An apparatus and procedure are described to determine position s pecific normalization coefficients for surface EMG of upper extremity muscu lature. Study design. Thirty-nine subjects were tested three times. Repeatability o f EMG measurements across test sessions was determined by computing intracl ass correlation coefficients. Two-way analysis of variance was used to test upper extremity position dependent differences in EMG measurements. Background. EMG measurements are susceptible to error from skin movement an d muscle length changes, both of which may occur when upper extremity posit ions vary. Normalization of the EMG signal without consideration for such p ositional influences may lead to erroneous conclusions regarding muscle act ivation during functional tasks. Method. An apparatus was designed that allowed subjects to perform three re petitions of maximum elbow flexion, forearm pronation, wrist extension, and wrist flexion with the forearm in neutral and pronated positions. Surface EMG was sampled from eight muscles. Mean EMG on maximum voluntary contracti on was computed, and resting EMG was subtracted to obtain EMG normalization coefficients. Results. Upper extremity position affected the EMG normalization coefficien t for biceps brachii, which was lower in the pronated position, and extenso r carpi radialis, which was higher in the pronated position (P < 0.00625). Conclusions,. The apparatus accommodates various combined positions of the elbow, forearm and wrist. The normalization procedure is efficient for test ing subjects who are being observed during functional tasks. Only two muscl es were affected by upper extremity position, but group trends were not alw ays consistent with individual behavior. This method would ensure the use o f appropriate EMG normalization coefficients regardless of individual varia tion.