| Absence of equifinality of hand position in a double-step unloading task. | |
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MedLine Citation:
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PMID: 20623112 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Equifinality, during arm reaching movements, relates to the capacity of the neuromuscular system to attain the same final position in the presence or absence of transient perturbations. There have been several controversies regarding equifinality in the literature. A brief elastic perturbation, applied during a fast arm movement or just before its initiation, typically does not affect final arm position. On the other hand, several experiments have shown that velocity-dependent perturbations, such as Coriolis force or negative damping, while transient in nature, have a significant effect on final arm position when compared to unperturbed movements. In this study, an unloading paradigm was used to study the role of reflexes with respect to equifinality. The effects on final arm position of suddenly decreasing a static load maintained by fourteen subjects were analyzed. Subjects maintained an initial load produced by a double-joint manipulandum moving in the horizontal plane. The load was suddenly decreased, either in one or in two successive steps with different time intervals, resulting in a rapid reflex-mediated change in arm position. Unloading led to short-latency changes in the activity of shoulder and elbow muscles and significant variations in tonic activity. It was found that the final hand position was shorter for double- versus single-step unloading if the time between two successive changes in load was greater than 100 ms. With a shorter time interval, the final hand positions were the same. This difference in final hand positions was inversely proportional to the hand velocity at the time of the second change in load. Further, agonist/antagonist co-activation increased in double-step unloading. Thus, the change in both the load and the movement velocity may influence the magnitude of the unloading reflex. This may be indicative of a dependence of stretch reflexes on velocity. Perturbation may cause a reflex-mediated increase in joint stiffness, which could explain why equifinality is not preserved after some perturbations, such as velocity-dependant external forces. |
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Authors:
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Nahid Norouzi-Gheidari; Philippe Archambault |
Publication Detail:
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Type: Journal Article Date: 2010-07-10 |
Journal Detail:
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Title: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale Volume: 205 ISSN: 1432-1106 ISO Abbreviation: Exp Brain Res Publication Date: 2010 Aug |
Date Detail:
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Created Date: 2010-08-03 Completed Date: 2010-11-22 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 0043312 Medline TA: Exp Brain Res Country: Germany |
Other Details:
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Languages: eng Pagination: 167-82 Citation Subset: IM |
Affiliation:
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School of Physical and Occupational Therapy, McGill University, Montreal, QC, Canada. Nahid.Norouzi@mail.mcgill.ca |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Adolescent Adult Arm / physiology Biomechanics Data Interpretation, Statistical Electromyography Female Hand / physiology* Humans Individuality Male Movement / physiology Muscle, Skeletal / physiology Psychomotor Performance / physiology* Robotics Space Perception / physiology* Young Adult |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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