Tonic postural lean after-effects influenced by support surface stability and dynamics.
Hum Mov Sci
; 30(2): 238-48, 2011 Apr.
Article
in En
| MEDLINE
| ID: mdl-20674053
ABSTRACT
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°) or on a toes-up sinusoidally tilted surface (7° ± 3°), 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.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Orientation
/
Posture
/
Proprioception
/
Space Perception
/
Postural Balance
/
Kinesthesis
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Muscle Contraction
Limits:
Adult
/
Female
/
Humans
/
Male
Language:
En
Journal:
Hum Mov Sci
Year:
2011
Type:
Article
Affiliation country:
United States