FATIGUE ASSOCIATED EMG BEHAVIOR OF THE FIRST DORSAL INTEROSSEOUS AND ADDUCTOR POLLICIS MUSCLES IN DIFFERENT GROUPS OF SUBJECTS

We have studied the fatigue-associated behavior of surface EMG in two histochemically different muscles of the hand: fi rst dorsal interosse ous (FDI) and adductor pollicis (AP; relatively more type I fibers in AP than in FDI). During a fatigue test evoked by electrical stimulatio n of the ulnar nerve, the mean amplitudes of compound muscle action po tentials (M-waves) exhibited the same overall pattern for both muscles : a rapid phase of potentiation followed by a gradual decline. However , if the group of subjects was subdivided on the basis of hand length, significant differences emerged in the reactions of AP: in large hand s, no fatigue-associated M-wave decline was seen, whereas in small han ds a distinct decline was observed. A possible explanation for this ph enomenon might be the presence of a greater amount of EMG contaminatio n from other muscles in smaller hands. In the supposedly ''cleaner'' r ecordings from larger hands, significant differences between FDI and A P were observed with regard to their fatigue-associated EMG reactions (M-wave depression in FDI but not in AP). The direction of these diffe rences was in accordance with expectations on the basis of known diffe rences in histochemical fiber type composition. (C) 1994 John Wiley & Sons, Inc.