COMPARATIVE ANALYSIS OF ELECTROMYOGRAPHIC MUSCLE ACTIVITY OF THE HUMAN HAND DURING CYCLIC TURNS OF ISOMETRIC EFFORT VECTOR OF WRIST IN OPPOSITE DIRECTIONS

The features of the formation of targeted tonic isometric effort created by muscles of the shoulder girdle and shoulder were compared for two opposite changes of the directions of arbitrary force vector-clockwise and counterclockwise. The magnitude of the effort vector remained constant. The intensity of the central motor commands (CMC) was evaluated according to the area of founded rectified, averaged and approximated electromyographic (EMG) recorded from the investigated muscles. The effort development was carried out in determined direction in operation space of the horizontal plane under angles of 75 degrees in the shoulder joint and 90 degrees in the elbow one. The synergic interaction of individual functional groups of muscles under certain reaction force was found. In the case of space, it was determined the main activity areas of the investigated muscles within the operating space. The differences were shown in the levels of EMG amplitude in opposite directions bypass of effort vector. Coactivation of flexor muscles was found, while the extensors showed their activity only within their functional sectors. Half of the investigated muscles showed an increase of the EMG amplitude for the counter-clockwise direction in relation to EMG amplitude for the clockwise direction. This can be attributed to more complex patterns of motor commands organization which consistently addressed to the muscles of the shoulder and forearm caused by atypical sequence of activation of antagonist muscles under making hand movements in cyclic mode during tonic isometric contraction.