Article

Changing the foot position modifies the mechanical action exerted by the ankle
extensor and flexor muscles over the body. We verified, in two groups of healthy
subjects standing with the heels touching or apart, whether a 90 degrees external
rotation of the right leg and foot also changes the pattern of vestibulospinal
reflexes elicited by electrical stimulation of the labyrinth.
With the head
oriented forward, leg rotation did not modify the labyrinthine-driven
displacements of the center of pressure (CoP). When the head was rotated in the
horizontal plane, either to the right or to the left, the CoP displacement
increased along the y axis in all subjects. Changes in the x component in most
instances appropriate to preserve unmodified the direction of body sway elicited
by the stimulus were observed. Right leg rotation increased the basal EMG
activity of ankle extensors and flexors on the left side, while the right side
activity was unaffected. The EMG responses to labyrinthine stimulation were
modified only on the left side, in a way appropriate to correct the effects of
the altered torque pattern exerted on the body by right leg muscles. It appears,
therefore, that somatosensory signals related to leg rotation and/or copy of the
corresponding voluntary motor commands modify the pattern of vestibulospinal
reflexes and maintain the postural response appropriate to counteract a body sway
in the direction inferred by labyrinthine signals.
CI - Copyright (c) 2010 Elsevier B.V. All rights reserved.

Langue : ANGLAIS