THE INFLUENCE OF TASK AND ANGLE ON TORQUE PRODUCTION AND MUSCLE-ACTIVITY AT THE ELBOW

This study investigated the effect of changing internal mechanical var iables and task demands on muscle activity and torque production durin g high effort isometric contractions of the elbow flexors. The effect of adding a 50% maximal voluntary contraction (MVC) of supination to a n MVC of elbow flexion was studied over a range of angles from 30 degr ees to 110 degrees of elbow flexion. Surface EMGs were recorded from t he biceps brachii (BIG), brachioradialis (BRAD) and triceps brachii (T RI) of 10 healthy subjects. BIC was the only muscle to show a consiste nt trend of increasing root mean square (rms) EMG with increasing elbo w flexion angle. BIC activity also remained constant or increased with the addition of the supination task at all angles. In contrast, BRAD showed decreased activity when supination was added at several angular positions. Maximal flexion torque was reduced when the second task of submaximal supination was added. This torque reduction was statistica lly significant at all angles except 70 degrees and appeared related t o the decreased contribution from BRAD. In a small subset of subjects, however, BRAD activity did not decrease when the second degrees of fr eedom (df) task was added. These subjects exhibited higher flexion tor ques averaged over task than the majority, at all angles except 30 deg rees. These data support the view that internal mechanical considerati ons influence the manner in which the central nervous system (CNS) dis tributes activity to muscular synergists in response to altered task d emands. Further, subject-specific patterns exist which must be recogni zed if these findings are to be incorporated in training or rehabilita tion programmes.