AUTHOR=Kostyukov Alexander I. , Lehedza Oleksii V. , Gorkovenko Andrii V. , Abramovych Tetiana I. , Pilewska Wieslawa , Mischenko Viktor S. , Zasada Mariusz 

TITLE=Hysteresis and Synergy of the Central Commands to Muscles Participating in Parafrontal Upper Limb Movements

JOURNAL=Frontiers in Physiology

VOLUME=Volume 10 - 2019

YEAR=2019

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.01441

DOI=10.3389/fphys.2019.01441

ISSN=1664-042X

ABSTRACT=The averaged electromyograms (EMGs) were registered from the elbow and shoulder muscles of ten adult men in isotonic movements of the right hand performed under visual guidance on the horizontal plane along linear trajectories going parallel to the frontal plane at various distances from the trunk. The reciprocating movements with a constant velocity 4 cm/sec, directed first on the right and then on the left, were produced under consecutive actions of two identic isotonic loads (10.2 N) applied to the hand in the right- (Fr) or leftward (Fl) directions. The elbow and shoulder flexors reacted predominantly on Fr loads; the extensors were mostly activated by Fl loads. Under the action of the corresponding loads, positional changes of the averaged EMGs in both flexor and extensor muscles belonging to different joints demonstrated hysteresis properties; the counterclockwise direction of the hysteresis loops was always registered in flexors and the clockwise direction in extensors. The muscles predominantly opposing the loading forces of a given direction participate in a cocontraction mode as antagonists when the direction of load is changed; in this case, together with a decrease in the amplitude of the hysteresis loops, their direction is also reversed. The multiplication index of synergy (MIS), which is based on multiplication of the respective normalized averaged EMG records, has been proposed to evaluate quantitatively changes in the synergy effects between various muscle groups. For distal shifts of the movement traces, the synergy effects are shown to be changed in different directions, increasing in flexors and decreasing in extensors. The obtained results allow us to conclude that the hysteresis properties of muscle contraction and the related characteristics of signal transmission in the motor control system lead to a strong hysteresis-like modification of central commands coming to the muscles in various movement tasks.