Objective: This study determined the nature of bimanual deficits during visually-guided isometric force production in chronic stroke. Methods: Stroke survivors and age-matched controls performed bimanual isometric wrist/finger extension contractions for 20. s to target submaximal force levels. Force asymmetry was indexed by the proportion of force contributed by the impaired hand to total force. Force coordination was determined by computing time-series cross-correlations and time-lag between force outputs of both hands. Results: The stroke group demonstrated greater asymmetry and reduced coordination in force produced by each hand. The extent of asymmetry in the force magnitude remained constant across the three submaximal force levels in both groups. Bimanual force coordination increased at higher forces in controls but not in stroke. Finally, the less-impaired hand forces time-lagged the impaired hand. Conclusions: Bimanual motor impairments in chronic stroke are characterized by increased asymmetry and reduced coordination between individual hand forces. Distinct control mechanisms are involved in the production and coordination of forces following stroke. Significance: An implication involves rehabilitation protocols that emphasize bimanual coordination for training the hands to produce symmetric forces that are temporally coordinated. © 2011.
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