Document Detail

Static prehension of a horizontally oriented object in three dimensions.
MedLine Citation:
PMID:  22071684     Owner:  NLM     Status:  MEDLINE    
We studied static prehension of a horizontally oriented object. Specific hypotheses were explored addressing such issues as the sharing patterns of the total moment of force across the digits, presence of mechanically unnecessary digit forces, and trade-off between multi-digit synergies at the two levels of the assumed control hierarchy. Within the assumed hierarchy, at the upper level, the task is shared between the thumb and virtual finger (an imagined finger producing a wrench equal to the sum of the wrenches of individual fingers). At the lower level, action of the virtual finger is shared among the four actual fingers. The subjects held statically a horizontally oriented handle instrumented with six-component force/torque sensors with different loads and torques acting about the long axis of the handle. The thumb acted from above while the four fingers supported the weight of the object. When the external torque was zero, the thumb produced mechanically unnecessary force of about 2.8 N, which did not depend on the external load magnitude. When the external torque was not zero, tangential forces produced over 80% of the total moment of force. The normal forces by the middle and ring fingers produced consistent moments against the external torque, while the normal forces of the index and little fingers did not. Force and moment variables at both hierarchical levels were stabilized by covaried across trials adjustments of forces/moments produced by individual digits with the exception of the normal force analyzed at the lower level of the hierarchy. There was a trade-off between synergy indices computed at the two levels of the hierarchy for the three components of the total force vector, but not for the moment of force components. Overall, the results have shown that task mechanics are only one factor that defines forces produced by individual digits. Other factors, such as loading sensory receptors may lead to mechanically unnecessary forces. There seems to be no single rule (for example, ensuring similar safety margin values) that would describe sharing of the normal and tangential forces and be valid across tasks. Fingers that are traditionally viewed as less accurate (e.g., the ring finger) may perform more consistently in certain tasks. The observations of the trade-off between the synergy indices computed at two levels for the force variables but not for the moment of force variables suggest that the degree of redundancy (the number of excessive elemental variables) at the higher level is an important factor.
Yen-Hsun Wu; Vladimir M Zatsiorsky; Mark L Latash
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural     Date:  2011-11-10
Journal Detail:
Title:  Experimental brain research     Volume:  216     ISSN:  1432-1106     ISO Abbreviation:  Exp Brain Res     Publication Date:  2012 Jan 
Date Detail:
Created Date:  2012-01-16     Completed Date:  2012-05-03     Revised Date:  2014-09-20    
Medline Journal Info:
Nlm Unique ID:  0043312     Medline TA:  Exp Brain Res     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  249-61     Citation Subset:  IM    
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MeSH Terms
Data Interpretation, Statistical
Fingers / physiology
Hand / physiology*
Hand Strength / physiology*
Orientation / physiology*
Psychomotor Performance
Space Perception / physiology*
Weight Perception / physiology
Young Adult
Grant Support

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

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