Search

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.

Electromyogramms (EMG) of eight muscles of the arm were analyzed in 11 healthy men aged 25-40 years during equal magnitude isometric efforts created by wrist. Subjects had to track cursor that moved around on the screen at a constant speed (16 degrees/s) in a horizontal plane. Thus, the subject slowly changed the direction of generation of efforts, while its amplitude remained constant. It was established that during creation of the static efforts equal in all directions, the extensors activity was mainly in the areas of extension of shoulder and elbow joints, whereas the flexor activity was observed in all directions with maximum, which corresponded to the arm bending. It is assumed that muscular activity is organized on the principle of the synergies that are clearly related to the task and beyond it can not exist.