Coordination of the dynamic phases of EMG activity in human elbow flexors in the performance of targeted tracking movements |
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Authors: | A N Tal’nov S G Serenko V L Cherkasskii S S Strafun |
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Institution: | (1) Bogomolets Institute of Physiology, National Academy of Sciences of Ukraine, Kyiv, Ukraine;(2) Ukraininan Institute of Traumatology and Orthopedics, Ministry of Public Health of Ukraine, Kyiv, Ukraine;(3) Department of Neurosurgery, University of Pittsburg, USA |
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Abstract: | The EMG pattern in the elbow flexors during the performance of relatively slow (non-ballistic) targeted flexor and extensor
movements with different velocities and amplitudes and subsequent fixation of a reached position was studied in healthy humans.
Using a servocontrolled mechanostimulator, steady external loading was applied to the arm, which provided performance of the
movements and their termination exclusively by the flexor activity, leaving the extensors passive. In all cases, even at very
slow movements, EMG activity of the flexors at transition of the joint from one equilibrium state to another was shown to
contain a clear dynamic phase followed by a phase of stationary activity. The level of the latter, generated during fixation
of a reached position, was practically independent of the amplitude of a movement within the 0–60° range of the joint angles.
Thus, the force developed by the flexors at the dynamic EMG phase became fixed when a new equilibrium joint position was reached
and did not decrease in the course of a considerable drop in the efferent activity level, when the stationary phase of this
activity began. The dynamic EMG phase included two components. The first component was related to leaving the equilibrium
state with a certain acceleration, while the second component was probably involved in the velocity control and stoppage of
the joint in a new equilibrium position. We suppose that retention of the joint in the equilibrium state is not provided exclusively
by formation of a certain equilibrium level of efferent activity (as it is postulated by the equilibrium point hypotheses);
it results from some coordinated modifications of the dynamic muscle activity that provide achievement of equilibrium in a
certain position within a certain stage of the movement. |
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