Positioning Errors in Simple Targeted Movements of the Forearm Realized in the Absence of Visual Control: Effects of Vibrational Stimulation of Antagonist Muscles

Abstract

In 17 healthy subjects, we examined the characteristics of targeted movements of the forearm, flexion from the initial position of full extension taken as 0 deg to a 50 deg target angle in the elbow joint (flexor tests, FTs) and extension from the initial angle of 100 deg to the same target angle (extensor tests, ETs) with return to the initial positions. A standard movement (its trajectory corresponded to a simple trapezium) was performed under conditions of visual feedback (the value of the target angle and trajectory of the movement were visualized on the screen of a monitor); then, this movement should be reproduced by the subject (according to an acoustic signal) in the absence of visual control. Target-reaching test movements in the absence of visual feedback differed from the standard ones in a higher velocity. Blindfold reproduction of standard movements realized under kinesthetic control was accompanied in all subjects by noticeable positive systematic errors of targeted positioning (in the group, on average, 5.16 ± 0.55 and 4.83 ± 0.58 deg under FT and ET conditions, respectively). Vibrational stimulation of the muscles whose activity mainly provided the movement and positioning (m. biceps brachii in the FT cases and m. triceps brachii in the case of ETs) resulted in decreases of the errors of kinesthetic positioning; intragroup means of these errors were 2.55 ± 0.36 deg (FTs) and 2.26 ± 0.40 deg (ETs). The positioning errors demonstrated even greater decreases upon vibrational stimulation of the muscles, which were relatively inactive under conditions of the tests and underwent passive stretching in the course of the movements (m. triceps in FTs and m. biceps in ETs). Mean intragroup values of the errors in these cases were 0.46 ± 0.25 and 0.52 ± 0.31 deg, respectively. The nature of systematic positioning errors in the reproduction of targeted movements in the absence of visual control and the mechanisms underlying the influence of vibrational stimulation of the muscles involved in realization of these movements on the positioning errors under kinesthetic control are discussed.