ANTICIPATORY POSTURAL ADJUSTMENTS DURING SELF-INITIATED PERTURBATIONSOF DIFFERENT MAGNITUDE TRIGGERED BY A STANDARD MOTOR ACTION

The purpose of the study was to define whether anticipatory postural a djustments scale with the magnitude of a self-triggered postural pertu rbation when a standard motor action triggers the perturbation. Standi ng subjects generated vertical forces of different magnitude with thei r extended arms against a bar connected through a rigid cord to the ho ot. They released the bar with a standard bilateral shoulder abduction . Anticipatory postural adjustments were seen as changes in the level and/or timing of the background activation of postural muscles. Muscle s of the dorsal part of the legs and of the trunk demonstrated an anti cipatory decrease in the level of activation, commonly leading to its complete disappearance. There was no relation between the magnitude of the unloading and the timing of the changes in the background activit y of these muscles. Muscles of the frontal part of the legs and of the trunk demonstrated an anticipatory increase in their activity whose t iming and amplitude correlated positively with the magnitude of the pe rturbation. We conclude that anticipatory postural adjustments can be scaled with respect to the magnitude of a self-triggered perturbation. Copyright (C) 1996 Elsevier Science Ireland Ltd.