Abramovych T. Activation of the muscles of the human arms during slow two-joint movements

Thesis is devoted to analysis of the central motor commands (CMCs) arriving to the muscles of human arms during fulfillment: 1) cyclic movements of the hand under action of the constant tangential elastic load; 2) synchronous bimanual “rowing-type” movements. Amplitudes of the full-wave rectified and averaged EMGs were used to estimate intensities of the CMCs. The EMGs recorded from the elbow and shoulder muscles were compared for four possible combinations in directions of the movement and the applied load. The EMG intensities were significantly correlated with the force torques at the corresponding joints. Motor commands of circular two-joint movements of the hand are mainly associated with the torque changes at the shoulder and elbow joints, being modulated in accordance with the eccentric or concentric type of the muscle contractions at different parts of the movement trajectories. The features of the functional interaction (synergies) of muscles during coordinated movements of the shoulder links and forearms during the test movements are described. The influence of the velocity factor on the dynamic components of the CMCs was revealed. Statistically significant differences between the EMG amplitudes during the "pull" and "push" movements were registered in each of the muscles; differences in dynamic and static EMG components under the action of external loads of different directions were also significant. It has been shown that the CMCs coming to the elbow flexors were more variable (“flexible”) compared to the shoulder extensors. With an increase in the duration of the active phases of movement, the amplitudes of the dynamic EMG components D1 and D2 decreased for both directions of the external load in all studied muscles. The level of synchronization and EMG - activity “in rowing-type movements” of the left and right arm muscles of the same name tended to decrease in the presence of visual feedback. It could be assumed that in the presence of visual feedback, the cognitive influence on the control of “rowing-type movements” is heightened, so such movements become to closer to the bimanual, visually controlled movements.