1998 ISEK CONGRESS KEYNOTE LECTURE - MULTIMUSCLE CONTROL IN HUMAN MOVEMENTS

It has been suggested that the coordination of the activity of multipl e muscles results from the comparison of the actual configuration of t he body with a referent configuration specified by the nervous system so that the recruitment and gradation of the activity of each skeletal muscle depend on the difference between these two configurations. Act ive movements may be produced by the modification of the referent conf iguration. The hypothesis predicts the existence of a global minimum i n electromyographic (EMG) activity of multiple muscles during movement s involving reversals in direction. This prediction was tested in five subjects by analysing movements resembling the act of reaching for an object placed beyond one's reach from a sitting position. In such mov ements, initially sitting subjects raise their body to a semi-standing position and then return to sitting. Consistent with the hypothesis i s the observation of a global minimum in the surface EMG activity of 1 6 muscles of the arm, trunk and leg at a specific phase of the movemen t, When the minimum occurred, EMG activity of each muscle did not exce ed 2-7% of its maximal activity during the movement. As predicted, glo bal EMG minima occurred at the phase corresponding to the reversal in movement direction, that is, during the transition from raising to low ering of the body. The global EMG minimum may represent the point at w hich temporal matching occurs between the actual and the referent body configurations. This study implies a specific link between motor beha vior and the geometric shape of the body modified by the brain accordi ng to the desired action. (C) 1998 Elsevier Science Ltd. All rights re served.