Manifestations of Hysteresis in EMG Activity of Muscles of the Human Upper Limb in Generation of Cyclic Isometric Efforts

Manifestations of muscle hysteresis were examined in seven subjects who generated cyclic isometric efforts by their upper limb in a two-joint mode. Force moments in generation of voluntary efforts with respect to the shoulder and elbow joints were measured, and averaged EMG activity was recorded from eight shoulder and shoulder girdle muscles at five different fixed positions of the upper limb. Hysteresis loops for EMG activity under conditions of two opposite directions of circulation of the isometric effort vectors (clockwise and counterclockwise) were compared. Significant disagreements between segments of increase ("advance") or decrease ("retardation") in the EMG amplitude with respect to zero values of the respective force movements were found. Directions of parametric hysteresis loops for EMG activity could be different both for a certain muscle against the background of different configurations of the upper limb links and for different subjects. It is supposed that there is no definite standard strategy for taking into account hysteresis effects in the control of motor phenomena; the CNS selects such specific individual strategy, which demonstrates its validity in the course of formation of the motor experience of an individual

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