Article

Tonic neuromuscular processes are evident during lean after-effects, which occur
after prolonged standing on a fixed ramp. Postural processes underlying lean
after-effects were examined here using dynamic surface conditions. Three tilt
adaptation conditions were tested with eyes-closed (n=11). Tilt adaptation
conditions involved standing for 120s on a fixed toes-up ramp
(7 degrees ) or on
a toes-up sinusoidally tilted surface (7 degrees +/- 3 degrees ), which was
followed by 120s of standing on either a fixed horizontal surface or
sway-referenced surface. All participants showed postural after-effects (p <
.003). Specifically, standing on a fixed horizontal surface after sine-tilt
adaptation, resulted in forward leaning which decayed over 120s back to baseline.
Standing on a sway-referenced surface after tilt-adaptation, initially showed no
lean after-effect, however over the course of the trial the center-of-pressure
shifted backward (p < .02). This after-effect during sway-reference conditions
was also evident in the sway-induced surface tilt, which increased in
dorsiflexion (p < .002), rather than decaying back to baseline. Thus, adaptation
occurs on a dynamically tilted surface, while reliability of the surface as a
stable reference affects the return of the center-of-pressure and surface tilt to
baseline. These findings relate to changes in flexor/extensor muscle tonic
set-point which also occur following a prolonged voluntary isometric contraction.
CI - Copyright (c) 2010 Elsevier B.V. All rights reserved.

Langue : ANGLAIS