Article

Anticipatory postural adjustments (APAs) prior to step execution are thought to
be immutable once released. Here we challenge this assumption by testing whether
APAs can be modified online if a body perturbation occurs during execution. Two
directions of perturbation (resisting and assisting) relative to the body weight
transfer were used during the execution of APAs. We found that APAs are modified
online (increase in both ground pressure and muscle activity) to compensate for
resisting perturbations. The outcomes of a biomechanical model confirmed that the
early changes in the APAs resulted from an active control of the APAs and were
not merely mechanical consequences of the perturbation. However, no modification
of the initial feedforward command was observed for assisting perturbations. The
motor command changes for the resisting perturbation may originate from the
mismatch between passively originated forces and those actively specified by the
central command when acting in the opposite direction.
The absence of a mismatch
in the assisting perturbation might explain why the central nervous system was
not prompted to modify the APAs in this condition.
CI - Copyright (c) 2011 Elsevier B.V. All rights reserved.

Langue : ANGLAIS