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Interactions with compliant loads alter stretch reflex gains but not intermuscular coordination.

Abstract：

:The human motor system regulates arm mechanics to produce stable postures during interactions with different physical environments. This occurs partly via involuntary mechanisms, including stretch reflexes. Previous single-joint studies demonstrated enhanced reflex sensitivity during interactions with compliant environments, suggesting reflex gain increases to enhance limb stability when that stability is not provided by the environment. This study examined whether similar changes in reflex gain are present throughout the limb following perturbations that simultaneously influence multiple joints. Furthermore, we investigated whether any observed modulation was accompanied by task-specific changes in reflex coordination across muscles, a question that cannot be addressed using single-joint perturbations. Reflexes were elicited during the maintenance of posture by perturbing the arm with a three degrees of freedom robot, configured to have isotropic stiffness of either 10 N/m (compliant) or 10 kN/m (stiff). Perturbation characteristics were matched in both environments. Reflex magnitude was quantified by the average rectified electromyogram, recorded from eight muscles crossing the elbow and shoulder. Reflex coordination was assessed using independent components analysis to compare reflex activation patterns during interactions with stiff and compliant environments. Stretch reflex sensitivity increased significantly in all muscles during interactions with the compliant environment and these changes were not due to changes in background muscle activity. However, there was no significant difference in the reflex coordination patterns observed during interactions with the stiff and compliant environments. These results suggest that reflex modulation occurred through altered use of fixed muscle coordination patterns rather than through a change in reflex coordination.

journal_name

J Neurophysiol

journal_title

Journal of neurophysiology

authors

Perreault EJ,Chen K,Trumbower RD,Lewis G

doi

10.1152/jn.01094.2007

subject

Has Abstract

pub_date

2008-05-01 00:00:00

pages

2101-13

issue

eissn

0022-3077

issn

1522-1598

pii

01094.2007

journal_volume

pub_type

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Interactions with compliant loads alter stretch reflex gains but not intermuscular coordination.