Article

Perturbation of whole-body stability often evokes rapid arm reactions. It has
been suggested that the earliest arm activation is a generic
(e.g. startle-like)
response to which a later stabilizing (e.g. counterweight or reach-to-grasp) or
impact-protection component can be appended. To examine whether the initial part
of the reaction is generic, we examined arm reactions evoked by small balance
perturbations in 12 healthy young adults while varying perturbation direction
(rightward or forward platform translation) and environmental conditions
(handrail present or absent). The perturbation magnitude was selected to be
sufficiently small to obviate the need to use the arms for stabilization. To
avoid adaptation or habituation, analysis focused on each subject's very first
exposure to the perturbation. Most subjects exhibited active movement of both
arms in reaction to the perturbation, but there was large (non-stereotypical)
inter-subject variation in muscle-onset latency and arm kinematics. Furthermore,
the velocity and direction of the initial arm movement were affected by
perturbation direction, in a manner consistent with functional strategies
(counterweight strategy in backward falls, hybrid counterweight/protective
strategy in leftward falls). Although subjects never contacted the handrail,
responses were slower when it was present. These results are not consistent with
a generic stereotyped response, but suggest instead that even the earliest
component of first-trial arm reactions was functionally modulated.
CI - Copyright (c) 2012 Elsevier B.V. All rights reserved.

Langue : ANGLAIS