Document Detail

Postural responses triggered by multidirectional leg lifts and surface tilts.
MedLine Citation:
PMID:  15940494     Owner:  NLM     Status:  MEDLINE    
The aim of the present study was to investigate the relationship between proactive and reactive components of postural control. We contrasted the kinematic and electromyographic (EMG) responses to multidirectional voluntary leg lifts with those elicited by unexpected surface tilts. In particular, we addressed the role of trunk stabilization following either a voluntary or forced weight shift from double to single limb support. Nine young female subjects stood with a standing posture of 45 degrees toe-out and their arms abducted to shoulder level. On the experimenter's signal, subjects either (1) lifted one leg as fast as possible in one of six directions (R/L side, R/L diagonal front, R/L diagonal back) to a height of 45 degrees or (2) maintained standing as the support surface tilted at a rate of 53 degrees /s to a height of 10 degrees in one of six directions (R/L-up, R/L diagonal toes-up, R/L diagonal toes-down). For both tasks, our results showed that the center of pressure (COP) displacement began before or in conjunction with displacement of the center of mass (COM), after which the COP oscillated about the horizontal projection of the COM. In addition, the muscles were recruited in a distal-to-proximal sequence, either in anticipation of the voluntary leg lift or in response to the sudden surface tilt. Thus, the COP was being used dynamically to control displacement of the COM. The axial postural strategy comprising head, trunk, and pelvis movements was quantified by means of principal component analysis. More than 95% of the variance in the data could be described by the first two eigenvectors, which revealed specific coordination patterns dominated by pelvis rotation in one direction and head/trunk rotation in the opposite direction. Unexpected surface tilting elicited an automatic response strategy that focused on controlling the orientation of the head and trunk with respect to the vertical gravity vector while trunk verticality was compromised for movement generation and the recovery of postural equilibrium during leg lifting. In conclusion, regardless of the type (voluntary versus involuntary) or direction of perturbation, the strategy employed by the central nervous system to control the body COM displacement concerns mainly trunk stabilization.
Lucinda K Hughey; Joyce Fung
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2005-06-07
Journal Detail:
Title:  Experimental brain research     Volume:  165     ISSN:  0014-4819     ISO Abbreviation:  Exp Brain Res     Publication Date:  2005 Aug 
Date Detail:
Created Date:  2005-08-31     Completed Date:  2005-12-08     Revised Date:  2013-12-13    
Medline Journal Info:
Nlm Unique ID:  0043312     Medline TA:  Exp Brain Res     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  152-66     Citation Subset:  IM    
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MeSH Terms
Biomechanical Phenomena
Central Nervous System / physiology
Eye Movements / physiology
Head Movements / physiology
Leg / physiology*
Movement / physiology*
Muscle, Skeletal / physiology*
Orientation / physiology
Pelvis / physiology
Postural Balance / physiology*
Posture / physiology*
Principal Component Analysis
Proprioception / physiology
Vestibule, Labyrinth / physiology
Weight-Bearing / physiology

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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