The Upper Extremity’s Postural Synergies, Ensuring the Motor Task Realization of Keeping the Balanced Position of the Object in the Hand

The article presents an analysis of postural and muscular synergies involved in the implementation of motor tasks to maintain the balanced position of an object in the hand while walking. During movement, electromyograms of the superficial muscles of the upper extremities were recorded and video recordings of body segment movements were performed. Synergy parameters were extracted from the recorded signals using factor analysis and the principal component methods. The assumption about the orientation of muscle synergies to stabilize the trajectories of the upper limb segments, which are important for the successful implementation of a motor task, was tested. A general postural synergy has been established that is used for various motor tasks, as well as higher-order synergies that fine-tune posture during movement. Four muscle synergies involved in controlling the movements of the upper extremity have been identified, two of which are the main ones. They are associated with compensation for balance disorders caused by the moments of placing the foot on the support, active extension of the lower limb in the knee and ankle joints. The spatial organization of muscle synergies shows individual strategies for using muscles in their structure, despite the fact that the same moments act as disturbing factors acting on the stabilizing system. Muscle synergies are activated at the moments of the greatest disturbing effect on postural stability and are aimed at stabilizing articular angles and trajectories of movements of the segments of the upper extremity.